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Versions: (draft-farinacci-lisp) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 RFC 6830

Network Working Group                                       D. Farinacci
Internet-Draft                                                 V. Fuller
Intended status: Experimental                                   D. Meyer
Expires: April 2, 2010                                          D. Lewis
                                                           cisco Systems
                                                      September 29, 2009


                 Locator/ID Separation Protocol (LISP)
                         draft-ietf-lisp-05.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on April 2, 2010.

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   Copyright (c) 2009 IETF Trust and the persons identified as the
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Abstract

   This draft describes a simple, incremental, network-based protocol to
   implement separation of Internet addresses into Endpoint Identifiers
   (EIDs) and Routing Locators (RLOCs).  This mechanism requires no
   changes to host stacks and no major changes to existing database
   infrastructures.  The proposed protocol can be implemented in a
   relatively small number of routers.

   This proposal was stimulated by the problem statement effort at the
   Amsterdam IAB Routing and Addressing Workshop (RAWS), which took
   place in October 2006.


Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  8
   4.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 14
   5.  Tunneling Details  . . . . . . . . . . . . . . . . . . . . . . 16
     5.1.  LISP IPv4-in-IPv4 Header Format  . . . . . . . . . . . . . 17
     5.2.  LISP IPv6-in-IPv6 Header Format  . . . . . . . . . . . . . 18
     5.3.  Tunnel Header Field Descriptions . . . . . . . . . . . . . 19
     5.4.  Dealing with Large Encapsulated Packets  . . . . . . . . . 21
       5.4.1.  A Stateless Solution to MTU Handling . . . . . . . . . 22
       5.4.2.  A Stateful Solution to MTU Handling  . . . . . . . . . 22
   6.  EID-to-RLOC Mapping  . . . . . . . . . . . . . . . . . . . . . 24
     6.1.  LISP IPv4 and IPv6 Control Plane Packet Formats  . . . . . 24
       6.1.1.  LISP Packet Type Allocations . . . . . . . . . . . . . 26
       6.1.2.  Map-Request Message Format . . . . . . . . . . . . . . 26
       6.1.3.  EID-to-RLOC UDP Map-Request Message  . . . . . . . . . 28
       6.1.4.  Map-Reply Message Format . . . . . . . . . . . . . . . 30
       6.1.5.  EID-to-RLOC UDP Map-Reply Message  . . . . . . . . . . 33
       6.1.6.  Map-Register Message Format  . . . . . . . . . . . . . 34
       6.1.7.  Encapsualted Control Message Format  . . . . . . . . . 36
     6.2.  Routing Locator Selection  . . . . . . . . . . . . . . . . 38
     6.3.  Routing Locator Reachability . . . . . . . . . . . . . . . 39
       6.3.1.  Echo Nonce Algorithm . . . . . . . . . . . . . . . . . 42
       6.3.2.  RLOC Probing Algorithm . . . . . . . . . . . . . . . . 43
     6.4.  Routing Locator Hashing  . . . . . . . . . . . . . . . . . 44
     6.5.  Changing the Contents of EID-to-RLOC Mappings  . . . . . . 45
       6.5.1.  Clock Sweep  . . . . . . . . . . . . . . . . . . . . . 45
       6.5.2.  Solicit-Map-Request (SMR)  . . . . . . . . . . . . . . 46
   7.  Router Performance Considerations  . . . . . . . . . . . . . . 48
   8.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 49
     8.1.  First-hop/Last-hop Tunnel Routers  . . . . . . . . . . . . 50



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     8.2.  Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 50
     8.3.  ISP Provider-Edge (PE) Tunnel Routers  . . . . . . . . . . 51
   9.  Traceroute Considerations  . . . . . . . . . . . . . . . . . . 52
     9.1.  IPv6 Traceroute  . . . . . . . . . . . . . . . . . . . . . 53
     9.2.  IPv4 Traceroute  . . . . . . . . . . . . . . . . . . . . . 53
     9.3.  Traceroute using Mixed Locators  . . . . . . . . . . . . . 53
   10. Mobility Considerations  . . . . . . . . . . . . . . . . . . . 55
     10.1. Site Mobility  . . . . . . . . . . . . . . . . . . . . . . 55
     10.2. Slow Endpoint Mobility . . . . . . . . . . . . . . . . . . 55
     10.3. Fast Endpoint Mobility . . . . . . . . . . . . . . . . . . 55
     10.4. Fast Network Mobility  . . . . . . . . . . . . . . . . . . 57
     10.5. LISP Mobile Node Mobility  . . . . . . . . . . . . . . . . 57
   11. Multicast Considerations . . . . . . . . . . . . . . . . . . . 59
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 60
   13. Prototype Plans and Status . . . . . . . . . . . . . . . . . . 61
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 64
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 64
     14.2. Informative References . . . . . . . . . . . . . . . . . . 65
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 68
   Appendix B.  Document Change Log . . . . . . . . . . . . . . . . . 69
     B.1.  Changes to draft-ietf-lisp-05.txt  . . . . . . . . . . . . 69
     B.2.  Changes to draft-ietf-lisp-04.txt  . . . . . . . . . . . . 69
     B.3.  Changes to draft-ietf-lisp-03.txt  . . . . . . . . . . . . 71
     B.4.  Changes to draft-ietf-lisp-02.txt  . . . . . . . . . . . . 71
     B.5.  Changes to draft-ietf-lisp-01.txt  . . . . . . . . . . . . 72
     B.6.  Changes to draft-ietf-lisp-00.txt  . . . . . . . . . . . . 72
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 73
























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1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].














































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2.  Introduction

   Many years of discussion about the current IP routing and addressing
   architecture have noted that its use of a single numbering space (the
   "IP address") for both host transport session identification and
   network routing creates scaling issues (see [CHIAPPA] and [RFC1498]).
   A number of scaling benefits would be realized by separating the
   current IP address into separate spaces for Endpoint Identifiers
   (EIDs) and Routing Locators (RLOCs); among them are:

   1.  Reduction of routing table size in the "default-free zone" (DFZ).
       Use of a separate numbering space for RLOCs will allow them to be
       assigned topologically (in today's Internet, RLOCs would be
       assigned by providers at client network attachment points),
       greatly improving aggregation and reducing the number of
       globally-visible, routable prefixes.

   2.  More cost-effective multihoming for sites that connect to
       different service providers where they can control their own
       policies for packet flow into the site without using extra
       routing table resources of core routers.

   3.  Easing of renumbering burden when clients change providers.
       Because host EIDs are numbered from a separate, non-provider-
       assigned and non-topologically-bound space, they do not need to
       be renumbered when a client site changes its attachment points to
       the network.

   4.  Traffic engineering capabilities that can be performed by network
       elements and do not depend on injecting additional state into the
       routing system.  This will fall out of the mechanism that is used
       to implement the EID/RLOC split (see Section 4).

   5.  Mobility without address changing.  Existing mobility mechanisms
       will be able to work in a locator/ID separation scenario.  It
       will be possible for a host (or a collection of hosts) to move to
       a different point in the network topology either retaining its
       home-based address or acquiring a new address based on the new
       network location.  A new network location could be a physically
       different point in the network topology or the same physical
       point of the topology with a different provider.

   This draft describes protocol mechanisms to achieve the desired
   functional separation.  For flexibility, the mechanism used for
   forwarding packets is decoupled from that used to determine EID to
   RLOC mappings.  This document covers the former.  For the later, see
   [CONS], [ALT], [EMACS], [RPMD], and [NERD].  This work is in response
   to and intended to address the problem statement that came out of the



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   RAWS effort [RFC4984].

   The Routing and Addressing problem statement can be found in [RADIR].

   This draft focuses on a router-based solution.  Building the solution
   into the network will facilitate incremental deployment of the
   technology on the Internet.  Note that while the detailed protocol
   specification and examples in this document assume IP version 4
   (IPv4), there is nothing in the design that precludes use of the same
   techniques and mechanisms for IPv6.  It should be possible for IPv4
   packets to use IPv6 RLOCs and for IPv6 EIDs to be mapped to IPv4
   RLOCs.

   Related work on host-based solutions is described in Shim6 [SHIM6]
   and HIP [RFC4423].  Related work on a router-based solution is
   described in [GSE].  This draft attempts to not compete or overlap
   with such solutions and the proposed protocol changes are expected to
   complement a host-based mechanism when Traffic Engineering
   functionality is desired.

   Some of the design goals of this proposal include:

   1.  Require no hardware or software changes to end-systems (hosts).

   2.  Minimize required changes to Internet infrastructure.

   3.  Be incrementally deployable.

   4.  Require no router hardware changes.

   5.  Minimize the number of routers which have to be modified.  In
       particular, most customer site routers and no core routers
       require changes.

   6.  Minimize router software changes in those routers which are
       affected.

   7.  Avoid or minimize packet loss when EID-to-RLOC mappings need to
       be performed.

   There are 4 variants of LISP, which differ along a spectrum of strong
   to weak dependence on the topological nature and possible need for
   routability of EIDs.  The variants are:








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   LISP 1:  uses EIDs that are routable through the RLOC topology for
      bootstrapping EID-to-RLOC mappings.  [LISP1] This was intended as
      a prototyping mechanism for early protocol implementation.  It is
      now deprecated and should not be deployed.

   LISP 1.5:  uses EIDs that are routable for bootstrapping EID-to-RLOC
      mappings; such routing is via a separate topology.

   LISP 2:  uses EIDS that are not routable and EID-to-RLOC mappings are
      implemented within the DNS.  [LISP2]

   LISP 3:  uses non-routable EIDs that are used as lookup keys for a
      new EID-to-RLOC mapping database.  Use of Distributed Hash Tables
      [DHTs] [LISPDHT] to implement such a database would be an area to
      explore.  Other examples of new mapping database services are
      [CONS], [ALT], [RPMD], [NERD], and [APT].

   This document on LISP 1.5, and LISP 3 variants, both of which rely on
   a router-based distributed cache and database for EID-to-RLOC
   mappings.  The LISP 1.0 mechanism works but does not allow reduction
   of routing information in the default-free-zone of the Internet.  The
   LISP 2 mechanisms are put on hold and may never come to fruition
   since it is not architecturally pure to have routing depend on
   directory and directory depend on routing.  The LISP 3 mechanisms
   will be documented elsewhere but may use the control-plane options
   specified in this specification.

























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3.  Definition of Terms

   Provider Independent (PI) Addresses:   an address block assigned from
      a pool where blocks are not associated with any particular
      location in the network (e.g. from a particular service provider),
      and is therefore not topologically aggregatable in the routing
      system.

   Provider Assigned (PA) Addresses:   a block of IP addresses that are
      assigned to a site by each service provider to which a site
      connects.  Typically, each block is sub-block of a service
      provider CIDR block and is aggregated into the larger block before
      being advertised into the global Internet.  Traditionally, IP
      multihoming has been implemented by each multi-homed site
      acquiring its own, globally-visible prefix.  LISP uses only
      topologically-assigned and aggregatable address blocks for RLOCs,
      eliminating this demonstrably non-scalable practice.

   Routing Locator (RLOC):   the IPv4 or IPv6 address of an egress
      tunnel router (ETR).  It is the output of a EID-to-RLOC mapping
      lookup.  An EID maps to one or more RLOCs.  Typically, RLOCs are
      numbered from topologically-aggregatable blocks that are assigned
      to a site at each point to which it attaches to the global
      Internet; where the topology is defined by the connectivity of
      provider networks, RLOCs can be thought of as PA addresses.
      Multiple RLOCs can be assigned to the same ETR device or to
      multiple ETR devices at a site.

   Endpoint ID (EID):   a 32-bit (for IPv4) or 128-bit (for IPv6) value
      used in the source and destination address fields of the first
      (most inner) LISP header of a packet.  The host obtains a
      destination EID the same way it obtains an destination address
      today, for example through a DNS lookup or SIP exchange.  The
      source EID is obtained via existing mechanisms used to set a
      host's "local" IP address.  An EID is allocated to a host from an
      EID-prefix block associated with the site where the host is
      located.  An EID can be used by a host to refer to other hosts.
      EIDs MUST NOT be used as LISP RLOCs.  Note that EID blocks may be
      assigned in a hierarchical manner, independent of the network
      topology, to facilitate scaling of the mapping database.  In
      addition, an EID block assigned to a site may have site-local
      structure (subnetting) for routing within the site; this structure
      is not visible to the global routing system.  When used in
      discussions with other Locator/ID separation proposals, a LISP EID
      will be called a "LEID".  Throughout this document, any references
      to "EID" refers to an LEID.





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   EID-prefix:   A power-of-2 block of EIDs which are allocated to a
      site by an address allocation authority.  EID-prefixes are
      associated with a set of RLOC addresses which make up a "database
      mapping".  EID-prefix allocations can be broken up into smaller
      blocks when an RLOC set is to be associated with the smaller EID-
      prefix.  A globally routed address block (whether PI or PA) is not
      an EID-prefix.  However, a globally routed address block may be
      removed from global routing and reused as an EID-prefix.  A site
      that receives an explicitly allocated EID-prefix may not use that
      EID-prefix as a globally routed prefix assigned to RLOCs.

   End-system:   is an IPv4 or IPv6 device that originates packets with
      a single IPv4 or IPv6 header.  The end-system supplies an EID
      value for the destination address field of the IP header when
      communicating globally (i.e. outside of its routing domain).  An
      end-system can be a host computer, a switch or router device, or
      any network appliance.

   Ingress Tunnel Router (ITR):   a router which accepts an IP packet
      with a single IP header (more precisely, an IP packet that does
      not contain a LISP header).  The router treats this "inner" IP
      destination address as an EID and performs an EID-to-RLOC mapping
      lookup.  The router then prepends an "outer" IP header with one of
      its globally-routable RLOCs in the source address field and the
      result of the mapping lookup in the destination address field.
      Note that this destination RLOC may be an intermediate, proxy
      device that has better knowledge of the EID-to-RLOC mapping closer
      to the destination EID.  In general, an ITR receives IP packets
      from site end-systems on one side and sends LISP-encapsulated IP
      packets toward the Internet on the other side.

      Specifically, when a service provider prepends a LISP header for
      Traffic Engineering purposes, the router that does this is also
      regarded as an ITR.  The outer RLOC the ISP ITR uses can be based
      on the outer destination address (the originating ITR's supplied
      RLOC) or the inner destination address (the originating hosts
      supplied EID).

   TE-ITR:   is an ITR that is deployed in a service provider network
      that prepends an additional LISP header for Traffic Engineering
      purposes.

   Egress Tunnel Router (ETR):   a router that accepts an IP packet
      where the destination address in the "outer" IP header is one of
      its own RLOCs.  The router strips the "outer" header and forwards
      the packet based on the next IP header found.  In general, an ETR
      receives LISP-encapsulated IP packets from the Internet on one
      side and sends decapsulated IP packets to site end-systems on the



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      other side.  ETR functionality does not have to be limited to a
      router device.  A server host can be the endpoint of a LISP tunnel
      as well.

   TE-ETR:   is an ETR that is deployed in a service provider network
      that strips an outer LISP header for Traffic Engineering purposes.

   xTR:   is a reference to an ITR or ETR when direction of data flow is
      not part of the context description. xTR refers to the router that
      is the tunnel endpoint.  Used synonymously with the term "Tunnel
      Router".  For example, "An xTR can be located at the Customer Edge
      (CE) router", meaning both ITR and ETR functionality is at the CE
      router.

   EID-to-RLOC Cache:   a short-lived, on-demand table in an ITR that
      stores, tracks, and is responsible for timing-out and otherwise
      validating EID-to-RLOC mappings.  This cache is distinct from the
      full "database" of EID-to-RLOC mappings, it is dynamic, local to
      the ITR(s), and relatively small while the database is
      distributed, relatively static, and much more global in scope.

   EID-to-RLOC Database:   a global distributed database that contains
      all known EID-prefix to RLOC mappings.  Each potential ETR
      typically contains a small piece of the database: the EID-to-RLOC
      mappings for the EID prefixes "behind" the router.  These map to
      one of the router's own, globally-visible, IP addresses.

   Recursive Tunneling:   when a packet has more than one LISP IP
      header.  Additional layers of tunneling may be employed to
      implement traffic engineering or other re-routing as needed.  When
      this is done, an additional "outer" LISP header is added and the
      original RLOCs are preserved in the "inner" header.  Any
      references to tunnels in this specification refers to dynamic
      encapsulating tunnels and never are they statically configured.

   Reencapsulating Tunnels:   when a packet has no more than one LISP IP
      header (two IP headers total) and when it needs to be diverted to
      new RLOC, an ETR can decapsulate the packet (remove the LISP
      header) and prepends a new tunnel header, with new RLOC, on to the
      packet.  Doing this allows a packet to be re-routed by the re-
      encapsulating router without adding the overhead of additional
      tunnel headers.  Any references to tunnels in this specification
      refers to dynamic encapsulating tunnels and never are they
      statically configured.







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   LISP Header:   a term used in this document to refer to the outer
      IPv4 or IPv6 header, a UDP header, and a LISP header, an ITR
      prepends or an ETR strips.

   Address Family Indicator (AFI):   a term used to describe an address
      encoding in a packet.  An address family currently pertains to an
      IPv4 or IPv6 address.  See [AFI] for details.

   Negative Mapping Entry:   also known as a negative cache entry, is an
      EID-to-RLOC entry where an EID-prefix is advertised or stored with
      no RLOCs.  That is, the locator-set for the EID-to-RLOC entry is
      empty or has an encoded locator count of 0.  This type of entry
      could be used to describe a prefix from a non-LISP site, which is
      explicitly not in the mapping database.  There are a set of well
      defined actions that are encoded in a Negative Map-Reply.

   Data Probe:   a LISP-encapsulated data packet where the inner header
      destination address equals the outer header destination address
      used to trigger a Map-Reply by a decapsulating ETR.  In addition,
      the original packet is decapsulated and delivered to the
      destination host.  A Data Probe is used in some of the mapping
      database designs to "probe" or request a Map-Reply from an ETR; in
      other cases, Map-Requests are used.  See each mapping database
      design for details.



























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4.  Basic Overview

   One key concept of LISP is that end-systems (hosts) operate the same
   way they do today.  The IP addresses that hosts use for tracking
   sockets, connections, and for sending and receiving packets do not
   change.  In LISP terminology, these IP addresses are called Endpoint
   Identifiers (EIDs).

   Routers continue to forward packets based on IP destination
   addresses.  When a packet is LISP encapsulated, these addresses are
   referred to as Routing Locators (RLOCs).  Most routers along a path
   between two hosts will not change; they continue to perform routing/
   forwarding lookups on the destination addresses.  For routers between
   the source host and the ITR as well as routers from the ETR to the
   destination host, the destination address is an EID.  For the routers
   between the ITR and the ETR, the destination address is an RLOC.

   This design introduces "Tunnel Routers", which prepends LISP headers
   on host-originated packets and strip them prior to final delivery to
   their destination.  The IP addresses in this "outer header" are
   RLOCs.  During end-to-end packet exchange between two Internet hosts,
   an ITR prepends a new LISP header to each packet and an egress tunnel
   router strips the new header.  The ITR performs EID-to-RLOC lookups
   to determine the routing path to the the ETR, which has the RLOC as
   one of its IP addresses.

   Some basic rules governing LISP are:

   o  End-systems (hosts) only send to addresses which are EIDs.  They
      don't know addresses are EIDs versus RLOCs but assume packets get
      to LISP routers, which in turn, deliver packets to the destination
      the end-system has specified.

   o  EIDs are always IP addresses assigned to hosts.

   o  LISP routers mostly deal with Routing Locator addresses.  See
      details later in Section 4.1 to clarify what is meant by "mostly".

   o  RLOCs are always IP addresses assigned to routers; preferably,
      topologically-oriented addresses from provider CIDR blocks.

   o  When a router originates packets it may use as a source address
      either an EID or RLOC.  When acting as a host (e.g. when
      terminating a transport session such as SSH, TELNET, or SNMP), it
      may use an EID that is explicitly assigned for that purpose.  An
      EID that identifies the router as a host MUST NOT be used as an
      RLOC; an EID is only routable within the scope of a site.  A
      typical BGP configuration might demonstrate this "hybrid" EID/RLOC



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      usage where a router could use its "host-like" EID to terminate
      iBGP sessions to other routers in a site while at the same time
      using RLOCs to terminate eBGP sessions to routers outside the
      site.

   o  EIDs are not expected to be usable for global end-to-end
      communication in the absence of an EID-to-RLOC mapping operation.
      They are expected to be used locally for intra-site communication.

   o  EID prefixes are likely to be hierarchically assigned in a manner
      which is optimized for administrative convenience and to
      facilitate scaling of the EID-to-RLOC mapping database.  The
      hierarchy is based on a address allocation hierarchy which is not
      dependent on the network topology.

   o  EIDs may also be structured (subnetted) in a manner suitable for
      local routing within an autonomous system.

   An additional LISP header may be prepended to packets by a transit
   router (i.e.  TE-ITR) when re-routing of the path for a packet is
   desired.  An obvious instance of this would be an ISP router that
   needs to perform traffic engineering for packets in flow through its
   network.  In such a situation, termed Recursive Tunneling, an ISP
   transit acts as an additional ingress tunnel router and the RLOC it
   uses for the new prepended header would be either an TE-ETR within
   the ISP (along intra-ISP traffic engineered path) or in an TE-ETR
   within another ISP (an inter-ISP traffic engineered path, where an
   agreement to build such a path exists).

   This specification mandates that no more than two LISP headers get
   prepended to a packet.  This avoids excessive packet overhead as well
   as possible encapsulation loops.  It is believed two headers is
   sufficient, where the first prepended header is used at a site for
   Location/Identity separation and second prepended header is used
   inside a service provider for Traffic Engineering purposes.

   Tunnel Routers can be placed fairly flexibly in a multi-AS topology.
   For example, the ITR for a particular end-to-end packet exchange
   might be the first-hop or default router within a site for the source
   host.  Similarly, the egress tunnel router might be the last-hop
   router directly-connected to the destination host.  Another example,
   perhaps for a VPN service out-sourced to an ISP by a site, the ITR
   could be the site's border router at the service provider attachment
   point.  Mixing and matching of site-operated, ISP-operated, and other
   tunnel routers is allowed for maximum flexibility.  See Section 8 for
   more details.





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4.1.  Packet Flow Sequence

   This section provides an example of the unicast packet flow with the
   following conditions:

   o  Source host "host1.abc.com" is sending a packet to
      "host2.xyz.com", exactly what host1 would do if the site was not
      using LISP.

   o  Each site is multi-homed, so each tunnel router has an address
      (RLOC) assigned from the service provider address block for each
      provider to which that particular tunnel router is attached.

   o  The ITR(s) and ETR(s) are directly connected to the source and
      destination, respectively.

   o  Data Probes are used to solicit Map-Replies versus using Map-
      Requests.  And the Data Probes are sent on the underlying topology
      (the LISP 1.0 variant) but could also be sent over an alternative
      topology (the LISP 1.5 variant) as it would in [ALT].

   Client host1.abc.com wants to communicate with server host2.xyz.com:

   1.  host1.abc.com wants to open a TCP connection to host2.xyz.com.
       It does a DNS lookup on host2.xyz.com.  An A/AAAA record is
       returned.  This address is used as the destination EID and the
       locally-assigned address of host1.abc.com is used as the source
       EID.  An IPv4 or IPv6 packet is built using the EIDs in the IPv4
       or IPv6 header and sent to the default router.

   2.  The default router is configured as an ITR.  The ITR must be able
       to map the EID destination to an RLOC of the ETR at the
       destination site.  The ITR prepends a LISP header to the packet,
       with one of its RLOCs as the source IPv4 or IPv6 address.  The
       destination EID from the original packet header is used as the
       destination IPv4 or IPv6 in the prepended LISP header.
       Subsequent packets, where the outer destination address is the
       destination EID will be sent until EID-to-RLOC mapping is
       learned.

   3.  In LISP 1, the packet is routed through the Internet as it is
       today.  In LISP 1.5, the packet is routed on a different topology
       which may have EID prefixes distributed and advertised in an
       aggregatable fashion.  In either case, the packet arrives at the
       ETR.  The router is configured to "punt" the packet to the
       router's processor.  See Section 7 for more details.  For LISP
       2.0 and 3.0, the behavior is not fully defined yet.




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   4.  The LISP header is stripped so that the packet can be forwarded
       by the router control plane.  The router looks up the destination
       EID in the router's EID-to-RLOC database (not the cache, but the
       configured data structure of RLOCs).  An EID-to-RLOC Map-Reply
       message is originated by the ETR and is addressed to the source
       RLOC in the LISP header of the original packet (this is the ITR).
       The source RLOC of the Map-Reply is one of the ETR's RLOCs.

   5.  The ITR receives the Map-Reply message, parses the message (to
       check for format validity) and stores the mapping information
       from the packet.  This information is put in the ITR's EID-to-
       RLOC mapping cache (this is the on-demand cache, the cache where
       entries time out due to inactivity).

   6.  Subsequent packets from host1.abc.com to host2.xyz.com will have
       a LISP header prepended by the ITR using the appropriate RLOC as
       the LISP header destination address learned from the ETR.  Note,
       the packet may be sent to a different ETR than the one which
       returned the Map-Reply due to the source site's hashing policy or
       the destination site's locator-set policy.

   7.  The ETR receives these packets directly (since the destination
       address is one of its assigned IP addresses), strips the LISP
       header and forwards the packets to the attached destination host.

   In order to eliminate the need for a mapping lookup in the reverse
   direction, an ETR MAY create a cache entry that maps the source EID
   (inner header source IP address) to the source RLOC (outer header
   source IP address) in a received LISP packet.  Such a cache entry is
   termed a "gleaned" mapping and only contains a single RLOC for the
   EID in question.  More complete information about additional RLOCs
   SHOULD be verified by sending a LISP Map-Request for that EID.  Both
   ITR and the ETR may also influence the decision the other makes in
   selecting an RLOC.  See Section 6 for more details.

















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5.  Tunneling Details

   This section describes the LISP Data Message which defines the
   tunneling header used to encapsulate IPv4 and IPv6 packets which
   contain EID addresses.  Even though the following formats illustrate
   IPv4-in-IPv4 and IPv6-in-IPv6 encapsulations, the other 2
   combinations are supported as well.

   Since additional tunnel headers are prepended, the packet becomes
   larger and in theory can exceed the MTU of any link traversed from
   the ITR to the ETR.  It is recommended, in IPv4 that packets do not
   get fragmented as they are encapsulated by the ITR.  Instead, the
   packet is dropped and an ICMP Too Big message is returned to the
   source.

   Based on informal surveys of large ISP traffic patterns, it appears
   that most transit paths can accommodate a path MTU of at least 4470
   bytes.  The exceptions, in terms of data rate, number of hosts
   affected, or any other metric are expected to be vanishingly small.

   To address MTU concerns, mainly raised on the RRG mailing list, the
   LISP deployment process will include collecting data during its pilot
   phase to either verify or refute the assumption about minimum
   available MTU.  If the assumption proves true and transit networks
   with links limited to 1500 byte MTUs are corner cases, it would seem
   more cost-effective to either upgrade or modify the equipment in
   those transit networks to support larger MTUs or to use existing
   mechanisms for accommodating packets that are too large.

   For this reason, there is currently no plan for LISP to add any new
   additional, complex mechanism for implementing fragmentation and
   reassembly in the face of limited-MTU transit links.  If analysis
   during LISP pilot deployment reveals that the assumption of
   essentially ubiquitous, 4470+ byte transit path MTUs, is incorrect,
   then LISP can be modified prior to protocol standardization to add
   support for one of the proposed fragmentation and reassembly schemes.
   Note that two simple existing schemes are detailed in Section 5.4.














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5.1.  LISP IPv4-in-IPv4 Header Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version|  IHL  |Type of Service|          Total Length         |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |         Identification        |Flags|      Fragment Offset    |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   OH  |  Time to Live | Protocol = 17 |         Header Checksum       |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                    Source Routing Locator                     |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                 Destination Routing Locator                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4341        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   L   |N|L|E|  rflags |                 Nonce                         |
   I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   S / |                       Locator Status Bits                     |
   P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version|  IHL  |Type of Service|          Total Length         |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |         Identification        |Flags|      Fragment Offset    |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   IH  |  Time to Live |    Protocol   |         Header Checksum       |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                           Source EID                          |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                         Destination EID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
















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5.2.  LISP IPv6-in-IPv6 Header Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |         Payload Length        | Next Header=17|   Hop Limit   |
   v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
   O   +                                                               +
   u   |                                                               |
   t   +                     Source Routing Locator                    +
   e   |                                                               |
   r   +                                                               +
       |                                                               |
   H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   d   |                                                               |
   r   +                                                               +
       |                                                               |
   ^   +                  Destination Routing Locator                  +
   |   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4341        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   L   |N|L|E|  rflags |                 Nonce                         |
   I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   S / |                       Locator Status Bits                     |
   P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        |  Next Header  |   Hop Limit   |
   v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
   I   +                                                               +
   n   |                                                               |
   n   +                          Source EID                           +
   e   |                                                               |
   r   +                                                               +
       |                                                               |
   H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   d   |                                                               |



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   r   +                                                               +
       |                                                               |
   ^   +                        Destination EID                        +
   \   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.3.  Tunnel Header Field Descriptions

   Inner Header:  is the inner header, preserved from the datagram
      received from the originating host.  The source and destination IP
      addresses are EIDs.

   Outer Header:  is the outer header prepended by an ITR.  The address
      fields contain RLOCs obtained from the ingress router's EID-to-
      RLOC cache.  The IP protocol number is "UDP (17)" from [RFC0768].
      The DF bit of the Flags field is set to 0 when the method in
      Section 5.4.1 is used and set to 1 when the method in
      Section 5.4.2 is used.

   UDP Header:  contains a ITR selected source port when encapsulating a
      packet.  See Section 6.4 for details on the hash algorithm used
      select a source port based on the 5-tuple of the inner header.
      The destination port MUST be set to the well-known IANA assigned
      port value 4341.

   UDP Checksum:  this field SHOULD be transmitted as zero by an ITR for
      either IPv4 [RFC0768] or IPv6 encapsulation [UDP-TUNNELS].  When a
      packet with a zero UDP checksum is received by an ETR, the ETR
      MUST accept the packet for decapsulation.  When an ITR transmits a
      non-zero value for the UDP checksum, it MUST send a correctly
      computed value in this field.  When an ETR receives a packet with
      a non-zero UDP checksum, it MAY choose to verify the checksum
      value.  If it chooses to perform such verification, and the
      verification fails, the packet MUST be silently dropped.  If the
      ETR chooses not to perform the verification, or performs the
      verification successfully, the packet MUST be accepted for
      decapsulation.  The handling of UDP checksums for all tunneling
      protocols, including LISP, is under active discussion within the
      IETF.  When that discussion concludes, any necessary changes will
      be made to align LISP with the outcome of the broader discussion.

   UDP Length:  for an IPv4 encapsulated packet, the inner header Total
      Length plus the UDP and LISP header lengths are used.  For an IPv6
      encapsulated packet, the inner header Payload Length plus the size
      of the IPv6 header (40 bytes) plus the size of the UDP and LISP



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      headers are used.  The UDP header length is 8 bytes.

   N: this is the nonce-present bit.  When this bit is set to 1, the
      low-order 24-bits of the first 32-bits of the LISP header contains
      a Nonce.  See section Section 6.3.1 for details.

   L: this is the Locator-Status-Bits field enabled bit.  When this bit
      is set to 1, the Locator-Status-Bits in the second 32-bits of the
      LISP header are in use.

   E: this is the echo-nonce-request bit.  When this bit is set to 1,
      the N bit must be 1.  This bit should be ignored and has no
      meaning when the N bit is set to 0.  See section Section 6.3.1 for
      details.

   rflags:  this 4-bit field is reserved for future flag use.  It is set
      to 0 on transmit and ignored on receipt.

   LISP Nonce:  is a 24-bit value that is randomly generated by an ITR
      when the N-bit is set to 1.  The nonce is also used when the E-bit
      is set to request the nonce value to be echoed by the other side
      when packets are returned.  When the E-bit is clear but the N-bit
      is set, an ITR is either echoing a previously requested echo-nonce
      or providing a random nonce.  See section Section 6.3.1 for more
      details.

   LISP Locator Status Bits:  in the LISP header are set by an ITR to
      indicate to an ETR the up/down status of the Locators in the
      source site.  Each RLOC in a Map-Reply is assigned an ordinal
      value from 0 to n-1 (when there are n RLOCs in a mapping entry).
      The Locator Status Bits are numbered from 0 to n-1 from the least
      significant bit of the 32-bit field.  When a bit is set to 1, the
      ITR is indicating to the ETR the RLOC associated with the bit
      ordinal has up status.  See Section 6.3 for details on how an ITR
      can determine other ITRs at the site are reachable.  When a site
      has multiple EID-prefixes which result in multiple mappings (where
      each could have a different locator-set), the Locator Status Bits
      setting in an encapsulated packet MUST reflect the mapping for the
      EID-prefix that the inner-header source EID address matches.

   When doing Recursive Tunneling or ITR/PTR encapsulation:

   o  The outer header Time to Live field (or Hop Limit field, in case
      of IPv6) SHOULD be copied from the inner header Time to Live
      field.

   o  The outer header Type of Service field (or the Traffic Class
      field, in the case of IPv6) SHOULD be copied from the inner header



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      Type of Service field (with one caveat, see below).

   When doing Re-encapsulated Tunneling:

   o  The new outer header Time to Live field SHOULD be copied from the
      stripped outer header Time to Live field.

   o  The new outer header Type of Service field SHOULD be copied from
      the stripped OH header Type of Service field (with one caveat, see
      below).

   Copying the TTL serves two purposes: first, it preserves the distance
   the host intended the packet to travel; second, and more importantly,
   it provides for suppression of looping packets in the event there is
   a loop of concatenated tunnels due to misconfiguration.

   The ECN field occupies bits 6 and 7 of both the IPv4 Type of Service
   field and the IPv6 Traffic Class field [RFC3168].  The ECN field
   requires special treatment in order to avoid discarding indications
   of congestion [RFC3168].  ITR encapsulation MUST copy the 2-bit ECN
   field from the inner header to the outer header.  Re-encapsulation
   MUST copy the 2-bit ECN field from the stripped outer header to the
   new outer header.  If the ECN field contains a congestion indication
   codepoint (the value is '11', the Congestion Experienced (CE)
   codepoint), then ETR decapsulation MUST copy the 2-bit ECN field from
   the stripped outer header to the surviving inner header that is used
   to forward the packet beyond the ETR.  These requirements preserve
   Congestion Experienced (CE) indications when a packet that uses ECN
   traverses a LISP tunnel and becomes marked with a CE indication due
   to congestion between the tunnel endpoints.

5.4.  Dealing with Large Encapsulated Packets

   In the event that the MTU issues mentioned above prove to be more
   serious than expected, this section proposes 2 simple mechanisms to
   deal with large packets.  One is stateless using IP fragmentation and
   the other is stateful using Path MTU Discovery [RFC1191].

   It is left to the implementor to decide if the stateless or stateful
   mechanism should be implemented.  Both or neither can be decided as
   well since it is a local decision in the ITR regarding how to deal
   with MTU issues.  Sites can interoperate with differing mechanisms.

   Both stateless and stateful mechanisms also apply to Reencapsulating
   and Recursive Tunneling.  So any actions reference below to an ITR
   also apply to an TE-ITR.





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5.4.1.  A Stateless Solution to MTU Handling

   An ITR stateless solution to handle MTU issues is described as
   follows:

   1.  Define an architectural constant S for the maximum size of a
       packet, in bytes, an ITR would receive from a source inside of
       its site.

   2.  Define L to be the maximum size, in bytes, a packet of size S
       would be after the ITR prepends the LISP header, UDP header, and
       outer network layer header of size H.

   3.  Calculate: S + H = L.

   When an ITR receives a packet from a site-facing interface and adds H
   bytes worth of encapsulation to yield a packet size of L bytes, it
   resolves the MTU issue by first splitting the original packet into 2
   equal-sized fragments.  A LISP header is then prepended to each
   fragment.  This will ensure that the new, encapsulated packets are of
   size (S/2 + H), which is always below the effective tunnel MTU.

   When an ETR receives encapsulated fragments, it treats them as two
   individually encapsulated packets.  It strips the LISP headers then
   forwards each fragment to the destination host of the destination
   site.  The two fragments are reassembled at the destination host into
   the single IP datagram that was originated by the source host.

   This behavior is performed by the ITR when the source host originates
   a packet with the DF field of the IP header is set to 0.  When the DF
   field of the IP header is set to 1, or the packet is an IPv6 packet
   originated by the source host, the ITR will drop the packet when the
   size is greater than L, and sends an ICMP Too Big message to the
   source with a value of S, where S is (L - H).

   When the outer header encapsulation uses an IPv4 header the DF bit is
   always set to 0.

   This specification recommends that L be defined as 1500.

5.4.2.  A Stateful Solution to MTU Handling

   An ITR stateful solution to handle MTU issues is describe as follows
   and was first introduced in [OPENLISP]:

   1.  The ITR will keep state of the effective MTU for each locator per
       mapping cache entry.  The effective MTU is what the core network
       can deliver along the path between ITR and ETR.



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   2.  When an IPv6 encapsulated packet or an IPv4 encapsulated packet
       with DF bit set to 1, exceeds what the core network can deliver,
       one of the intermediate routers on the path will send an ICMP Too
       Big message to the ITR.  The ITR will parse the ICMP message to
       determine which locator is affected by the effective MTU change
       and then record the new effective MTU value in the mapping cache
       entry.

   3.  When a packet is received by the ITR from a source inside of the
       site and the size of the packet is greater than the effective MTU
       stored with the mapping cache entry associated with the
       destination EID the packet is for, the ITR will send an ICMP Too
       Big message back to the source.  The packet size advertised by
       the ITR in the ICMP Too Big message is the effective MTU minus
       the LISP encapsulation length.

   Even though this mechanism is stateful, it has advantages over the
   stateless IP fragmentation mechanism, by not involving the
   destination host with reassembly of ITR fragmented packets.
































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6.  EID-to-RLOC Mapping

6.1.  LISP IPv4 and IPv6 Control Plane Packet Formats

   The following new UDP packet types are used to retrieve EID-to-RLOC
   mappings:


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version|  IHL  |Type of Service|          Total Length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Identification        |Flags|      Fragment Offset    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Time to Live | Protocol = 17 |         Header Checksum       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Source Routing Locator                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 Destination Routing Locator                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |           Source Port         |         Dest Port             |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                         LISP Message                          |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version| Traffic Class |           Flow Label                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Payload Length        | Next Header=17|   Hop Limit   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                     Source Routing Locator                    +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +



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       |                                                               |
       +                  Destination Routing Locator                  +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |           Source Port         |         Dest Port             |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                         LISP Message                          |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The LISP UDP-based messages are the Map-Request and Map-Reply
   messages.  When a UDP Map-Request is sent, the UDP source port is
   chosen by the sender and the destination UDP port number is set to
   4342.  When a UDP Map-Reply is sent, the source UDP port number is
   set to 4342 and the destination UDP port number is copied from the
   source port of either the Map-Request or the invoking data packet.

   The UDP Length field will reflect the length of the UDP header and
   the LISP Message payload.

   The UDP Checksum is computed and set to non-zero for Map-Request and
   Map-Reply messages.  It MUST be checked on receipt and if the
   checksum fails, the packet MUST be dropped.

   LISP-CONS [CONS] use TCP to send LISP control messages.  The format
   of control messages includes the UDP header so the checksum and
   length fields can be used to protect and delimit message boundaries.

   This main LISP specification is the authoritative source for message
   format definitions for the Map-Request and Map-Reply messages.















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6.1.1.  LISP Packet Type Allocations

   This section will be the authoritative source for allocating LISP
   Type values.  Current allocations are:


       Reserved:                          0    b'0000'
       LISP Map-Request:                  1    b'0001'
       LISP Map-Reply:                    2    b'0010'
       LISP Map-Register:                 3    b'0011'
       LISP Encapsulated Control Message: 8    b'1000'


6.1.2.  Map-Request Message Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=1 |A|M|P|S|           Reserved            | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Source-EID-AFI        |            ITR-AFI            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Source EID Address  ...                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                Originating ITR RLOC Address ...               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |   Reserved    | EID mask-len  |        EID-prefix-AFI         |
   Rec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                       EID-prefix  ...                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Map-Reply Record  ...                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Mapping Protocol Data                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:








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   Type:   1 (Map-Request)

   A: This is an authoritative bit, which is set to 0 for UDP-based Map-
      Requests sent by an ITR.

   M: When set, it indicates a Map-Reply Record segment is included in
      the Map-Request.

   P: Indicates that a Map-Request should be treated as a "piggyback"
      locator reachability probe.  The receiver should respond with a
      Map-Reply with the P bit set and the nonce copied from the Map-
      Request.  See section Section 6.3.2 for more details.

   S: This is the SMR bit.  See Section 6.5.2 for details.

   Reserved:  Set to 0 on transmission and ignored on receipt.

   Record Count:  The number of records in this Map-Request message.  A
      record is comprised of the portion of the packet that is labeled
      'Rec' above and occurs the number of times equal to Record Count.
      For this version of the protocol, a receiver MUST accept and
      process Map-Requests that contain one or more records, but a
      sender MUST only send Map-Requests containing one record.  Support
      for requesting multiple EIDs in a single Map-Request message will
      be specified in a future version of the protocol.

   Nonce:  An 8-byte random value created by the sender of the Map-
      Request.  This nonce will be returned in the Map-Reply.  The
      security of the LISP mapping protocol depends critically on the
      strength of the nonce in the Map-Request message.  The nonce
      SHOULD be generated by a properly seeded pseudo-random (or strong
      random) source.  See [RFC4086] for advice on generating security-
      sensitive random data.

   Source-EID-AFI:  Address family of the "Source EID Address" field.

   ITR-AFI:  Address family of the "Originating ITR RLOC Address" field.

   Source EID Address:  This is the EID of the source host which
      originated the packet which is invoking this Map-Request.  When
      Map-Requests are used for refreshing a map-cache entry or for
      RLOC-probing, the value 0 is used.

   Originating ITR RLOC Address:  Used to give the ETR the option of
      returning a Map-Reply in the address-family of this locator.






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   EID mask-len:  Mask length for EID prefix.

   EID-AFI:  Address family of EID-prefix according to [RFC2434]

   EID-prefix:  4 bytes if an IPv4 address-family, 16 bytes if an IPv6
      address-family.  When a Map-Request is sent by an ITR because a
      data packet is received for a destination where there is no
      mapping entry, the EID-prefix is set to the destination IP address
      of the data packet.  And the 'EID mask-len' is set to 32 or 128
      for IPv4 or IPv6, respectively.  When an xTR wants to query a site
      about the status of a mapping it already has cached, the EID-
      prefix used in the Map-Request has the same mask-length as the
      EID-prefix returned from the site when it sent a Map-Reply
      message.

   Map-Reply Record:  When the M bit is set, this field is the size of
      the "Record" field in the Map-Reply format.  This Map-Reply record
      contains the EID-to-RLOC mapping entry associated with the Source
      EID.  This allows the ETR which will receive this Map-Request to
      cache the data if it chooses to do so.

   Mapping Protocol Data:  See [CONS] or [ALT] for details.  This field
      is optional and present when the UDP length indicates there is
      enough space in the packet to include it.

6.1.3.  EID-to-RLOC UDP Map-Request Message

   A Map-Request is sent from an ITR when it needs a mapping for an EID,
   wants to test an RLOC for reachability, or wants to refresh a mapping
   before TTL expiration.  For the initial case, the destination IP
   address used for the Map-Request is the destination-EID from the
   packet which had a mapping cache lookup failure.  For the later 2
   cases, the destination IP address used for the Map-Request is one of
   the RLOC addresses from the locator-set of the map cache entry.  The
   source address is either an IPv4 or IPv6 RLOC address depending if
   the Map-Request is using an IPv4 versus IPv6 header, respectively.
   In all cases, the UDP source port number for the Map-Request message
   is a randomly allocated 16-bit value and the UDP destination port
   number is set to the well-known destination port number 4342.  A
   successful Map-Reply updates the cached set of RLOCs associated with
   the EID prefix range.

   Map-Requests can also be LISP encapsulated using UDP destination port
   4342 with a LISP type value set to "Encapsulated Control Message",
   when sent from an ITR to a Map-Resolver.  Likewise, Map-Requests are
   LISP encapsulated the same way from a Map-Server to an ETR.  Details
   on encapsulated Map-Requests and Map-Resolvers can be found in
   [LISP-MS].



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   Map-Requests MUST be rate-limited.  It is recommended that a Map-
   Request for the same EID-prefix be sent no more than once per second.

   An ITR that is configured with mapping database information (i.e. it
   is also an ETR) may optionally include those mappings in a Map-
   Request.  When an ETR configured to accept and verify such
   "piggybacked" mapping data receives such a Map-Request, it may
   originate a "verifying Map-Request", addressed to the original ITR.
   If the ETR has a map-cache entry that matches the "piggybacked" EID
   and the RLOC is in the locator-set for the entry, then it may send
   the "verifying Map-Request" to the original Map-Request source.  If
   not, then it MUST send it to the "piggybacked" EID.  Doing this
   forces the "verifying Map-Request" to go through the mapping database
   system to reach the authoritative source of information about that
   EID, guarding against RLOC-spoofing in in the "piggybacked" mapping
   data.



































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6.1.4.  Map-Reply Message Format



        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=2 |P|E|            Reserved               | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record  TTL                          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Locator Count | EID mask-len  | ACT |A|      Reserved         |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   |           Reserved            |            EID-AFI            |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-prefix                           |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | o |           Unused Flags      |R|           Loc-AFI             |
   | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Mapping Protocol Data                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:

   Type:   2 (Map-Reply)

   P: Indicates that the Map-Reply is in response to a "piggyback"
      locator reachability Map-Request.  The nonce field should contain
      a copy of the nonce value from the original Map-Request.  See
      section Section 6.3.2 for more details.

   E: Indicates that the ETR which sends this Map-Reply message is
      advertising that the site is enabled for the Echo-Nonce locator
      reachability algorithm.  See Section 6.3.1 for more details.

   Reserved:  Set to 0 on transmission and ignored on receipt.






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   Record Count:  The number of records in this reply message.  A record
      is comprised of that portion of the packet labeled 'Record' above
      and occurs the number of times equal to Record count.

   Nonce:  A 24-bit value set in a Data-Probe packet or a 64-bit value
      from the Map-Request is echoed in this Nonce field of the Map-
      Reply.

   Record TTL:  The time in minutes the recipient of the Map-Reply will
      store the mapping.  If the TTL is 0, the entry should be removed
      from the cache immediately.  If the value is 0xffffffff, the
      recipient can decide locally how long to store the mapping.

   Locator Count:  The number of Locator entries.  A locator entry
      comprises what is labeled above as 'Loc'.  The locator count can
      be 0 indicating there are no locators for the EID-prefix.

   EID mask-len:  Mask length for EID prefix.

   ACT:  This 3-bit field describes negative Map-Reply actions.  These
      bits are used only when the 'Locator Count' field is set to 0.
      The action bits are encoded only in Map-Reply messages.  The
      actions defined are used by an ITR or PTR when a destination EID
      matches a negative mapping cache entry.  Unassigned values should
      cause a map-cache entry to be created and, when packets match this
      negative cache entry, they will be dropped.  The current assigned
      values are:



      (0) Drop:  The packet is dropped silently.

      (1) Natively-Forward:  The packet is not encapsulated or dropped
         but natively forwarded.

      (2) Send-Map-Request:  The packet invokes sending a Map-Request.

   A: The Authoritative bit, when sent by a UDP-based message is always
      set by the ETR.  See [CONS] for TCP-based Map-Replies.

   EID-AFI:  Address family of EID-prefix according to [RFC2434].

   EID-prefix:  4 bytes if an IPv4 address-family, 16 bytes if an IPv6
      address-family.







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   Priority:  each RLOC is assigned a unicast priority.  Lower values
      are more preferable.  When multiple RLOCs have the same priority,
      they may be used in a load-split fashion.  A value of 255 means
      the RLOC MUST NOT be used for unicast forwarding.

   Weight:  when priorities are the same for multiple RLOCs, the weight
      indicates how to balance unicast traffic between them.  Weight is
      encoded as a percentage of total unicast packets that match the
      mapping entry.  If a non-zero weight value is used for any RLOC,
      then all RLOCs must use a non-zero weight value and then the sum
      of all weight values MUST equal 100.  If a zero value is used for
      any RLOC weight, then all weights MUST be zero and the receiver of
      the Map-Reply will decide how to load-split traffic.  See
      Section 6.4 for a suggested hash algorithm to distribute load
      across locators with same priority and equal weight values.  When
      a single RLOC exists in a mapping entry, the weight value MUST be
      set to 100 and ignored on receipt.

   M Priority:  each RLOC is assigned a multicast priority used by an
      ETR in a receiver multicast site to select an ITR in a source
      multicast site for building multicast distribution trees.  A value
      of 255 means the RLOC MUST NOT be used for joining a multicast
      distribution tree.

   M Weight:  when priorities are the same for multiple RLOCs, the
      weight indicates how to balance building multicast distribution
      trees across multiple ITRs.  The weight is encoded as a percentage
      of total number of trees build to the source site identified by
      the EID-prefix.  If a non-zero weight value is used for any RLOC,
      then all RLOCs must use a non-zero weight value and then the sum
      of all weight values MUST equal 100.  If a zero value is used for
      any RLOC weight, then all weights MUST be zero and the receiver of
      the Map-Reply will decide how to distribute multicast state across
      ITRs.

   Unused Flags:  set to 0 when sending and ignored on receipt.

   R: when this bit is set, the locator is known to be reachable from
      the Map-Reply sender's perspective.

   Locator:  an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field)
      assigned to an ETR or router acting as a proxy replier for the
      EID-prefix.  Note that the destination RLOC address MAY be an
      anycast address.  A source RLOC can be an anycast address as well.
      The source or destination RLOC MUST NOT be the broadcast address
      (255.255.255.255 or any subnet broadcast address known to the
      router), and MUST NOT be a link-local multicast address.  The
      source RLOC MUST NOT be a multicast address.  The destination RLOC



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      SHOULD be a multicast address if it is being mapped from a
      multicast destination EID.

   Mapping Protocol Data:  See [CONS] or [ALT] for details.  This field
      is optional and present when the UDP length indicates there is
      enough space in the packet to include it.

6.1.5.  EID-to-RLOC UDP Map-Reply Message

   When a Data Probe packet or a Map-Request triggers a Map-Reply to be
   sent, the RLOCs associated with the EID-prefix matched by the EID in
   the original packet destination IP address field will be returned.
   The RLOCs in the Map-Reply are the globally-routable IP addresses of
   the ETR but are not necessarily reachable; separate testing of
   reachability is required.

   Note that a Map-Reply may contain different EID-prefix granularity
   (prefix + length) than the Map-Request which triggers it.  This might
   occur if a Map-Request were for a prefix that had been returned by an
   earlier Map-Reply.  In such a case, the requester updates its cache
   with the new prefix information and granularity.  For example, a
   requester with two cached EID-prefixes that are covered by a Map-
   Reply containing one, less-specific prefix, replaces the entry with
   the less-specific EID-prefix.  Note that the reverse, replacement of
   one less-specific prefix with multiple more-specific prefixes, can
   also occur but not by removing the less-specific prefix rather by
   adding the more-specific prefixes which during a lookup will override
   the less-specific prefix.

   Replies SHOULD be sent for an EID-prefix no more often than once per
   second to the same requesting router.  For scalability, it is
   expected that aggregation of EID addresses into EID-prefixes will
   allow one Map-Reply to satisfy a mapping for the EID addresses in the
   prefix range thereby reducing the number of Map-Request messages.

   The addresses for a encapsulated data packets or Map-Request message
   are swapped and used for sending the Map-Reply.  The UDP source and
   destination ports are swapped as well.  That is, the source port in
   the UDP header for the Map-Reply is set to the well-known UDP port
   number 4342.

   Map-Reply records can have an empty locator-set.  This type of a Map-
   Reply is called a Negative Map-Reply.  Negative Map-Replies convey
   special actions by the sender to the ITR or PTR which have solicited
   the Map-Reply.  There are two primary applications for Negative Map-
   Replies.  The first is for a Map-Resolver to instruct an ITR or PTR
   when a destination is for a LISP site versus a non-LISP site.  And
   the other is to source quench Map-Requests which are sent for non-



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   allocated EIDs.

   For each Map-Reply record, the list of locators in a locator-set MUST
   appear in the same order for each ETR that originates a Map-Reply
   message.  The locator-set MUST be sorted in order of ascending IP
   address where an IPv4 locator address is considered numerically 'less
   than' an IPv6 locator address.

6.1.6.  Map-Register Message Format

   The usage details of the Map-Register message can be found in
   specification [LISP-MS].  This section solely defines the message
   format.

   The message is sent in UDP with a destination UDP port of 4342 and a
   randomly selected UDP source port number.

   The Map-Register message format is:

































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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=3 |P|            Reserved                 | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Key ID             |  Authentication Data Length   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                     Authentication Data                       ~
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record  TTL                          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Locator Count | EID mask-len  | ACT |A|      Reserved         |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   |           Reserved            |            EID-AFI            |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-prefix                           |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | o |           Unused Flags      |R|           Loc-AFI             |
   | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:

   Type:   3 (Map-Register)

   P: Set to 1 by an ETR which sends a Map-Register message requesting
      for the Map-Server to proxy Map-Reply.  The Map-Server will send
      non-authoritative Map-Replies on behalf of the ETR.  Details on
      this usage will be provided in a future version of this draft.

   Reserved:  Set to 0 on transmission and ignored on receipt.

   Record Count:  The number of records in this Map-Register message.  A
      record is comprised of that portion of the packet labeled 'Record'
      above and occurs the number of times equal to Record count.

   Nonce:  This 8-byte Nonce field is set to 0 in Map-Register messages.






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   Key ID:  A configured ID to find the configured Message
      Authentication Code (MAC) algorithm and key value used for the
      authentication function.

   Authentication Data Length:  The length in bytes of the
      Authentication Data field that follows this field.  The length of
      the the Authentication Data field is dependent on the Message
      Authentication Code (MAC) algorithm used.  The length field allows
      a device that doesn't know the MAC algorithm to correctly parse
      the packet.

   Authentication Data:  The message digest used from the output of the
      Message Authentication Code (MAC) algorithm.  The entire Map-
      Register payload is authenticated with this field preset to 0.
      After the MAC is computed, it is placed in this field.
      Implementations of this specification MUST include support for
      HMAC-SHA-1-96 [RFC2404] and support for HMAC-SHA-128-256 [RFC4634]
      is recommended.

   The definition of the rest of the Map-Register can be found in the
   Map-Reply section.

6.1.7.  Encapsualted Control Message Format

   An Encapsulated Control Message is used to encapsulate control
   packets sent between xTRs and the mapping database system described
   in [LISP-MS].
























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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |                       IPv4 or IPv6 Header                     |
   OH  |                      (uses RLOC addresses)                    |
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4342        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   LH  |Type=8 |                   Reserved                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |                       IPv4 or IPv6 Header                     |
   IH  |                  (uses RLOC or EID addresses)                 |
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = yyyy        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   LCM |                      LISP Control Message                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Packet header descriptions:

   OH:   The outer IPv4 or IPv6 header which uses RLOC addresses in the
      source and destination header address fields.

   UDP:   The outer UDP header with destination port 4342.  The source
      port is randomly allocated.  The checksum field MUST be non-zero.

   LH:   Type 8 is defined to be a "LISP Encapsulated Control Message"
      and what follows is either an IPv4 or IPv6 header as encoded by
      the first 4 bits after the reserved field.

   IH:   The inner IPv4 or IPv6 header which can use either RLOC or EID
      addresses in the header address fields.  When a Map-Request is
      encapsulated in this packet format the destination address in this
      header is an EID.

   UDP:   The inner UDP header where the port assignments depends on the
      control packet being encapsulated.  When the control packet is a
      Map-Request or Map-Register, the source port is randomly assigned
      and the destination port is 4342.  When the control packet is a
      Map-Reply, the source port is 4342 and the destination port is
      assigned from the source port of the invoking Map-Request.  Port
      number 4341 MUST NOT be assigned to either port.  The checksum



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      field MUST be non-zero.

   LCM:   The format is one of the control message formats described in
      this section.  At this time, only Map-Request messages and PIM
      Join-Prune messages [MLISP] are allowed to be encapsulated.
      Encapsulating other types of LISP control messages are for further
      study.

6.2.  Routing Locator Selection

   Both client-side and server-side may need control over the selection
   of RLOCs for conversations between them.  This control is achieved by
   manipulating the Priority and Weight fields in EID-to-RLOC Map-Reply
   messages.  Alternatively, RLOC information may be gleaned from
   received tunneled packets or EID-to-RLOC Map-Request messages.

   The following enumerates different scenarios for choosing RLOCs and
   the controls that are available:

   o  Server-side returns one RLOC.  Client-side can only use one RLOC.
      Server-side has complete control of the selection.

   o  Server-side returns a list of RLOC where a subset of the list has
      the same best priority.  Client can only use the subset list
      according to the weighting assigned by the server-side.  In this
      case, the server-side controls both the subset list and load-
      splitting across its members.  The client-side can use RLOCs
      outside of the subset list if it determines that the subset list
      is unreachable (unless RLOCs are set to a Priority of 255).  Some
      sharing of control exists: the server-side determines the
      destination RLOC list and load distribution while the client-side
      has the option of using alternatives to this list if RLOCs in the
      list are unreachable.

   o  Server-side sets weight of 0 for the RLOC subset list.  In this
      case, the client-side can choose how the traffic load is spread
      across the subset list.  Control is shared by the server-side
      determining the list and the client determining load distribution.
      Again, the client can use alternative RLOCs if the server-provided
      list of RLOCs are unreachable.

   o  Either side (more likely on the server-side ETR) decides not to
      send a Map-Request.  For example, if the server-side ETR does not
      send Map-Requests, it gleans RLOCs from the client-side ITR,
      giving the client-side ITR responsibility for bidirectional RLOC
      reachability and preferability.  Server-side ETR gleaning of the
      client-side ITR RLOC is done by caching the inner header source
      EID and the outer header source RLOC of received packets.  The



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      client-side ITR controls how traffic is returned and can alternate
      using an outer header source RLOC, which then can be added to the
      list the server-side ETR uses to return traffic.  Since no
      Priority or Weights are provided using this method, the server-
      side ETR must assume each client-side ITR RLOC uses the same best
      Priority with a Weight of zero.  In addition, since EID-prefix
      encoding cannot be conveyed in data packets, the EID-to-RLOC cache
      on tunnel routers can grow to be very large.

   o  A "gleaned" map-cache entry, one learned from the source RLOC of a
      received encapsulated packet, is only stored and used for a few
      seconds, pending verification.  Verification is performed by
      sending a Map-Request to the source EID (the inner header IP
      source address) of the received encapsulated packet.  A reply to
      this "verifying Map-Request" is used to fully populate the map-
      cache entry for the "gleaned" EID and is stored and used for the
      time indicated from the TTL field of a received Map-Reply.  When a
      verified map-cache entry is stored, data gleaning no longer occurs
      for subsequent packets which have a source EID that matches the
      EID-prefix of the verified entry.

   RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be
   reachable when the R-bit for the locator record is set to 1.  Neither
   the information contained in a Map-Reply or that stored in the
   mapping database system provide reachability information for RLOCs.
   Such reachability needs to be determined separately, using one or
   more of the Routing Locator Reachability Algorithms described in the
   next section.

6.3.  Routing Locator Reachability

   Several mechanisms for determining RLOC reachability are currently
   defined:

   1.  An ETR may examine the Loc-Status-Bits in the LISP header of an
       encapsulated data packet received from an ITR.  If the ETR is
       also acting as an ITR and has traffic to return to the original
       ITR site, it can use this status information to help select an
       RLOC.

   2.  An ITR may receive an ICMP Network or ICMP Host Unreachable
       message for an RLOC it is using.  This indicates that the RLOC is
       likely down.

   3.  An ITR which participates in the global routing system can
       determine that an RLOC is down if no BGP RIB route exists that
       matches the RLOC IP address.




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   4.  An ITR may receive an ICMP Port Unreachable message from a
       destination host.  This occurs if an ITR attempts to use
       interworking [INTERWORK] and LISP-encapsulated data is sent to a
       non-LISP-capable site.

   5.  An ITR may receive a Map-Reply from a ETR in response to a
       previously sent Map-Request.  The RLOC source of the Map-Reply is
       likely up since the ETR was able to send the Map-Reply to the
       ITR.

   6.  When an ETR receives an encapsulated packet from an ITR, the
       source RLOC from the outer header of the packet is likely up.

   7.  An ITR/ETR pair can use the Locator Reachability Algorithms
       described in this section, namely Echo-Noncing or RLOC-Probing.

   When determining Locator up/down reachability by examining the Loc-
   Status-Bits from the LISP encapsulated data packet, an ETR will
   receive up to date status from an encapsulating ITR about
   reachability for all ETRs at the site.  CE-based ITRs at the source
   site can determine reachability relative to each other using the site
   IGP as follows:

   o  Under normal circumstances, each ITR will advertise a default
      route into the site IGP.

   o  If an ITR fails or if the upstream link to its PE fails, its
      default route will either time-out or be withdrawn.

   Each ITR can thus observe the presence or lack of a default route
   originated by the others to determine the Locator Status Bits it sets
   for them.

   RLOCs listed in a Map-Reply are numbered with ordinals 0 to n-1.  The
   Loc-Status-Bits in a LISP encapsulated packet are numbered from 0 to
   n-1 starting with the least significant bit.  For example, if an RLOC
   listed in the 3rd position of the Map-Reply goes down (ordinal value
   2), then all ITRs at the site will clear the 3rd least significant
   bit (xxxx x0xx) of the Loc-Status-Bits field for the packets they
   encapsulate.

   When an ETR decapsulates a packet, it will check for any change in
   the Loc-Status-Bits field.  When a bit goes from 1 to 0, the ETR will
   refrain from encapsulating packets to an RLOC that is indicated as
   down.  It will only resume using that RLOC if the corresponding Loc-
   Status-Bit returns to a value of 1.  Loc-Status-Bits are associated
   with a locator-set per EID-prefix.  Therefore, when a locator becomes
   unreachable, the Loc-Status-Bit that corresponds to that locator's



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   position in the list returned by the last Map-Reply will be set to
   zero for that particular EID-prefix.

   When ITRs at the site are not deployed in CE routers, the IGP can
   still be used to determine the reachability of Locators provided they
   are injected into the IGP.  This is typically done when a /32 address
   is configured on a loopback interface.

   When ITRs receive ICMP Network or Host Unreachable messages as a
   method to determine unreachability, they will refrain from using
   Locators which are described in Locator lists of Map-Replies.
   However, using this approach is unreliable because many network
   operators turn off generation of ICMP Unreachable messages.

   If an ITR does receive an ICMP Network or Host Unreachable message,
   it MAY originate its own ICMP Unreachable message destined for the
   host that originated the data packet the ITR encapsulated.

   Also, BGP-enabled ITRs can unilaterally examine the BGP RIB to see if
   a locator address from a locator-set in a mapping entry matches a
   prefix.  If it does not find one and BGP is running in the Default
   Free Zone (DFZ), it can decide to not use the locator even though the
   Loc-Status-Bits indicate the locator is up.  In this case, the path
   from the ITR to the ETR that is assigned the locator is not
   available.  More details are in [LOC-ID-ARCH].

   Optionally, an ITR can send a Map-Request to a Locator and if a Map-
   Reply is returned, reachability of the Locator has been determined.
   Obviously, sending such probes increases the number of control
   messages originated by tunnel routers for active flows, so Locators
   are assumed to be reachable when they are advertised.

   This assumption does create a dependency: Locator unreachability is
   detected by the receipt of ICMP Host Unreachable messages.  When an
   Locator has been determined to be unreachable, it is not used for
   active traffic; this is the same as if it were listed in a Map-Reply
   with priority 255.

   The ITR can test the reachability of the unreachable Locator by
   sending periodic Requests.  Both Requests and Replies MUST be rate-
   limited.  Locator reachability testing is never done with data
   packets since that increases the risk of packet loss for end-to-end
   sessions.

   When an ETR decapsulates a packet, it knows that it is reachable from
   the encapsulating ITR because that is how the packet arrived.  In
   most cases, the ETR can also reach the ITR but cannot assume this to
   be true due to the possibility of path asymmetry.  In the presence of



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   unidirectional traffic flow from an ITR to an ETR, the ITR should not
   use the lack of return traffic as an indication that the ETR is
   unreachable.  Instead, it must use an alternate mechanisms to
   determine reachability.

6.3.1.  Echo Nonce Algorithm

   When there is bidirectional data flow between a pair of locators, a
   simple mechanism called "nonce echoing" can be used to determine
   reachability between an ITR and ETR.  When an ITR wants to solicit a
   nonce echo, it sets the N and E bits and places a 24-bit nonce in the
   LISP header of the next encapsulated data packet.

   When this packet is received by the ETR, the encapsulated packet is
   forwarded as normal.  When the ETR next sends a data packet to the
   ITR, it includes the nonce received earlier with the N bit set and E
   bit cleared.  The ITR sees this "echoed nonce" and knows the path to
   and from the ETR is up.

   The ITR will set the E-bit and N-bit for every packet it sends while
   in echo-nonce-request state.  The time the ITR waits to process the
   echoed nonce before it determines the path is unreachable is variable
   and a choice left for the implementation.

   If the ITR is receiving packets from the ETR but does not see the
   nonce echoed while being in echo-nonce-request state, then the path
   to the ETR is unreachable.  This decision may be overridden by other
   locator reachability algorithms.  Once the ITR determines the path to
   the ETR is down it can switch to another locator for that EID-prefix.

   Note that "ITR" and "ETR" are relative terms here.  Both devices must
   be implementing both ITR and ETR functionality for the echo nonce
   mechanism to operate.

   The ITR and ETR may both go into echo-nonce-request state at the same
   time.  The number of packets sent or the time during which echo nonce
   requests are sent is an implementation specific setting.  However,
   when an ITR is in echo-nonce-request state, it can echo the ETR's
   nonce in the next set of packets that it encapsulates and then
   subsequently, continue sending echo-nonce-request packets.

   This mechanism does not completely solve the forward path
   reachability problem as traffic may be unidirectional.  That is, the
   ETR receiving traffic at a site may not may not be the same device as
   an ITR which transmits traffic from that site or the site to site
   traffic is unidirectional so there is no ITR returning traffic.

   The echo-nonce algorithm is bilateral.  That is, if one side sets the



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   E-bit and the other side is not enabled for echo-noncing, then the
   echoing of the nonce does not occur and the requesting side may
   regard the locator unreachable erroneously.  An ITR should only set
   the E-bit in a encapsulated data packet when it knows the ETR is
   enabled for echo-noncing.  This is conveyed by the E-bit in the Map-
   Reply message.

   Note that other locator reachability mechanisms are being researched
   and can be used to compliment or even override the Echo Nonce
   Algorithm.  See next section for an example of control-plane probing.

6.3.2.  RLOC Probing Algorithm

   RLOC Probing is a method that an ITR or PTR can use to determine the
   reachability status of one or more locators that it has cached in a
   map-cache entry.  The P-bit (Probe Bit) of the Map-Request and Map-
   Reply messages are used for RLOC Probing.

   RLOC probing is done in the control-plane on a timer basis where an
   ITR or PTR will originate a Map-Request destined to a locator address
   from one of its own locator addresses.  A Map-Request used as an
   RLOC-probe is NOT encapsulated and NOT sent to a Map-Server or on the
   ALT like one would when soliciting mapping data.  The EID record
   encoded in the Map-Request is the EID-prefix of the map-cache entry
   cached by the ITR or PTR.  The ITR or PTR may include a mapping data
   record for its own database mapping information.

   When an ETR receives a Map-Request message with the P-bit set, it
   returns a Map-Reply with the P-bit set.  The source address of the
   Map-Reply is set from the destination address of the Map-Request and
   the destination address of the Map-Reply is set from the source
   address of the Map-Request.  The Map-Reply should contain mapping
   data for the EID-prefix contained in the Map-Request.  This provides
   the opportunity for the ITR or PTR, which sent the RLOC-probe to get
   mapping updates if there were changes to the ETR's database mapping
   entries.

   There are advantages and disadvantages of RLOC Probing.  The greatest
   benefit of RLOC Probing is that it can handle many failure scenarios
   allowing the ITR to determine when the path to a specific locator is
   reachable or has become unreachable, thus providing a robust
   mechanism for switching to using another locator from the cached
   locator.  RLOC Probing can also provide RTT estimates between a pair
   of locators which can be useful for network management purposes as
   well as for selecting low delay paths.  The major disadvantage of
   RLOC Probing is in the number of control messages required and the
   amount of bandwidth used to obtain those benefits, especially if the
   requirement for failure detection times are very small.



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   Continued research and testing will attempt to characterize the
   tradeoffs of failure detection times versus message overhead.

6.4.  Routing Locator Hashing

   When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to
   a requesting ITR, the locator-set for the EID-prefix may contain
   different priority values for each locator address.  When more than
   one best priority locator exists, the ITR can decide how to load
   share traffic against the corresponding locators.

   The following hash algorithm may be used by an ITR to select a
   locator for a packet destined to an EID for the EID-to-RLOC mapping:

   1.  Either a source and destination address hash can be used or the
       traditional 5-tuple hash which includes the source and
       destination addresses, source and destination TCP, UDP, or SCTP
       port numbers and the IP protocol number field or IPv6 next-
       protocol fields of a packet a host originates from within a LISP
       site.  When a packet is not a TCP, UDP, or SCTP packet, the
       source and destination addresses only from the header are used to
       compute the hash.

   2.  Take the hash value and divide it by the number of locators
       stored in the locator-set for the EID-to-RLOC mapping.

   3.  The remainder will be yield a value of 0 to "number of locators
       minus 1".  Use the remainder to select the locator in the
       locator-set.

   Note that when a packet is LISP encapsulated, the source port number
   in the outer UDP header needs to be set.  Selecting a random value
   allows core routers which are attached to Link Aggregation Groups
   (LAGs) to load-split the encapsulated packets across member links of
   such LAGs.  Otherwise, core routers would see a single flow, since
   packets have a source address of the ITR, for packets which are
   originated by different EIDs at the source site.  A suggested setting
   for the source port number computed by an ITR is a 5-tuple hash
   function on the inner header, as described above.

   Many core router implementations use a 5-tuple hash to decide how to
   balance packet load across members of a LAG.  The 5-tuple hash
   includes the source and destination addresses of the packet and the
   source and destination ports when the protocol number in the packet
   is TCP or UDP.  For this reason, UDP encoding is used for LISP
   encapsulation.





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6.5.  Changing the Contents of EID-to-RLOC Mappings

   Since the LISP architecture uses a caching scheme to retrieve and
   store EID-to-RLOC mappings, the only way an ITR can get a more up-to-
   date mapping is to re-request the mapping.  However, the ITRs do not
   know when the mappings change and the ETRs do not keep track of who
   requested its mappings.  For scalability reasons, we want to maintain
   this approach but need to provide a way for ETRs change their
   mappings and inform the sites that are currently communicating with
   the ETR site using such mappings.

   When a locator record is added to the end of a locator-set, it is
   easy to update mappings.  We assume new mappings will maintain the
   same locator ordering as the old mapping but just have new locators
   appended to the end of the list.  So some ITRs can have a new mapping
   while other ITRs have only an old mapping that is used until they
   time out.  When an ITR has only an old mapping but detects bits set
   in the loc-status-bits that correspond to locators beyond the list it
   has cached, it simply ignores them.

   When a locator record is removed from a locator-set, ITRs that have
   the mapping cached will not use the removed locator because the xTRs
   will set the loc-status-bit to 0.  So even if the locator is in the
   list, it will not be used.  For new mapping requests, the xTRs can
   set the locator address to 0 as well as setting the corresponding
   loc-status-bit to 0.  This forces ITRs with old or new mappings to
   avoid using the removed locator.

   If many changes occur to a mapping over a long period of time, one
   will find empty record slots in the middle of the locator-set and new
   records appended to the locator-set.  At some point, it would be
   useful to compact the locator-set so the loc-status-bit settings can
   be efficiently packed.

   We propose here two approaches for locator-set compaction, one
   operational and the other a protocol mechanism.  The operational
   approach uses a clock sweep method.  The protocol approach uses the
   concept of Solicit-Map-Requests.

6.5.1.  Clock Sweep

   The clock sweep approach uses planning in advance and the use of
   count-down TTLs to time out mappings that have already been cached.
   The default setting for an EID-to-RLOC mapping TTL is 24 hours.  So
   there is a 24 hour window to time out old mappings.  The following
   clock sweep procedure is used:





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   1.  24 hours before a mapping change is to take effect, a network
       administrator configures the ETRs at a site to start the clock
       sweep window.

   2.  During the clock sweep window, ETRs continue to send Map-Reply
       messages with the current (unchanged) mapping records.  The TTL
       for these mappings is set to 1 hour.

   3.  24 hours later, all previous cache entries will have timed out,
       and any active cache entries will time out within 1 hour.  During
       this 1 hour window the ETRs continue to send Map-Reply messages
       with the current (unchanged) mapping records with the TTL set to
       1 minute.

   4.  At the end of the 1 hour window, the ETRs will send Map-Reply
       messages with the new (changed) mapping records.  So any active
       caches can get the new mapping contents right away if not cached,
       or in 1 minute if they had the mapping cached.

6.5.2.  Solicit-Map-Request (SMR)

   Soliciting a Map-Request is a selective way for xTRs, at the site
   where mappings change, to control the rate they receive requests for
   Map-Reply messages.  SMRs are also used to tell remote ITRs to update
   the mappings they have cached.

   Since the xTRs don't keep track of remote ITRs that have cached their
   mappings, they can not tell exactly who needs the new mapping
   entries.  So an xTR will solicit Map-Requests from sites it is
   currently sending encapsulated data to, and only from those sites.
   The xTRs can locally decide the algorithm for how often and to how
   many sites it sends SMR messages.

   An SMR message is simply a bit set in a Map-Request message.  An ITR
   or PTR will send a Map-Request when they receive an SMR message.
   Both the SMR sender and the Map-Request responder must rate-limited
   these messages.

   The following procedure shows how a SMR exchange occurs when a site
   is doing locator-set compaction for an EID-to-RLOC mapping:

   1.  When the database mappings in an ETR change, the ETRs at the site
       begin to send Map-Requests with the SMR bit set for each locator
       in each map-cache entry the ETR caches.

   2.  A remote xTR which receives the SMR message will schedule sending
       a Map-Request message to the source locator address of the SMR
       message.  A newly allocated random nonce is selected and the EID-



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       prefix uses is the one copied from the SMR message.

   3.  The remote xTR retransmits the Map-Request slowly until it gets a
       Map-Reply while continuing to use the cached mapping.

   4.  The ETRs at the site with the changed mapping will reply to the
       Map-Request with a Map-Reply message provided the Map-Request
       nonce matches the nonce from the SMR.  The Map-Reply messages
       SHOULD be rate limited.  This is important to avoid Map-Reply
       implosion.

   5.  The ETRs, at the site with the changed mapping, records the fact
       that the site that sent the Map-Request has received the new
       mapping data in the mapping cache entry for the remote site so
       the loc-status-bits are reflective of the new mapping for packets
       going to the remote site.  The ETR then stops sending SMR
       messages.

   For security reasons an ITR MUST NOT process unsolicited Map-Replies.
   The nonce MUST be carried from SMR packet, into the resultant Map-
   Request, and then into Map-Reply to reduce spoofing attacks.

   To avoid map-cache entry corruption by a third-party, a sender of an
   SMR-based Map-Request must be verified.  If an ITR receives an SMR-
   based Map-Request and the source is not in the locator-set for the
   stored map-cache entry, then the responding Map-Request MUST be sent
   with an EID destination to the mapping database system.  Since the
   mapping database system is more secure to reach an authoritative ETR,
   it will deliver the Map-Request to the authoritative source of the
   mapping data.





















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7.  Router Performance Considerations

   LISP is designed to be very hardware-based forwarding friendly.  By
   doing tunnel header prepending [RFC1955] and stripping instead of re-
   writing addresses, existing hardware can support the forwarding model
   with little or no modification.  Where modifications are required,
   they should be limited to re-programming existing hardware rather
   than requiring expensive design changes to hard-coded algorithms in
   silicon.

   A few implementation techniques can be used to incrementally
   implement LISP:

   o  When a tunnel encapsulated packet is received by an ETR, the outer
      destination address may not be the address of the router.  This
      makes it challenging for the control plane to get packets from the
      hardware.  This may be mitigated by creating special FIB entries
      for the EID-prefixes of EIDs served by the ETR (those for which
      the router provides an RLOC translation).  These FIB entries are
      marked with a flag indicating that control plane processing should
      be performed.  The forwarding logic of testing for particular IP
      protocol number value is not necessary.  No changes to existing,
      deployed hardware should be needed to support this.

   o  On an ITR, prepending a new IP header is as simple as adding more
      bytes to a MAC rewrite string and prepending the string as part of
      the outgoing encapsulation procedure.  Many routers that support
      GRE tunneling [RFC2784] or 6to4 tunneling [RFC3056] can already
      support this action.

   o  When a received packet's outer destination address contains an EID
      which is not intended to be forwarded on the routable topology
      (i.e.  LISP 1.5), the source address of a data packet or the
      router interface with which the source is associated (the
      interface from which it was received) can be associated with a VRF
      (Virtual Routing/Forwarding), in which a different (i.e. non-
      congruent) topology can be used to find EID-to-RLOC mappings.














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8.  Deployment Scenarios

   This section will explore how and where ITRs and ETRs can be deployed
   and will discuss the pros and cons of each deployment scenario.
   There are two basic deployment trade-offs to consider: centralized
   versus distributed caches and flat, recursive, or re-encapsulating
   tunneling.

   When deciding on centralized versus distributed caching, the
   following issues should be considered:

   o  Are the tunnel routers spread out so that the caches are spread
      across all the memories of each router?

   o  Should management "touch points" be minimized by choosing few
      tunnel routers, just enough for redundancy?

   o  In general, using more ITRs doesn't increase management load,
      since caches are built and stored dynamically.  On the other hand,
      more ETRs does require more management since EID-prefix-to-RLOC
      mappings need to be explicitly configured.

   When deciding on flat, recursive, or re-encapsulation tunneling, the
   following issues should be considered:

   o  Flat tunneling implements a single tunnel between source site and
      destination site.  This generally offers better paths between
      sources and destinations with a single tunnel path.

   o  Recursive tunneling is when tunneled traffic is again further
      encapsulated in another tunnel, either to implement VPNs or to
      perform Traffic Engineering.  When doing VPN-based tunneling, the
      site has some control since the site is prepending a new tunnel
      header.  In the case of TE-based tunneling, the site may have
      control if it is prepending a new tunnel header, but if the site's
      ISP is doing the TE, then the site has no control.  Recursive
      tunneling generally will result in suboptimal paths but at the
      benefit of steering traffic to resource available parts of the
      network.

   o  The technique of re-encapsulation ensures that packets only
      require one tunnel header.  So if a packet needs to be rerouted,
      it is first decapsulated by the ETR and then re-encapsulated with
      a new tunnel header using a new RLOC.

   The next sub-sections will describe where tunnel routers can reside
   in the network.




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8.1.  First-hop/Last-hop Tunnel Routers

   By locating tunnel routers close to hosts, the EID-prefix set is at
   the granularity of an IP subnet.  So at the expense of more EID-
   prefix-to-RLOC sets for the site, the caches in each tunnel router
   can remain relatively small.  But caches always depend on the number
   of non-aggregated EID destination flows active through these tunnel
   routers.

   With more tunnel routers doing encapsulation, the increase in control
   traffic grows as well: since the EID-granularity is greater, more
   Map-Requests and Map-Replies are traveling between more routers.

   The advantage of placing the caches and databases at these stub
   routers is that the products deployed in this part of the network
   have better price-memory ratios then their core router counterparts.
   Memory is typically less expensive in these devices and fewer routes
   are stored (only IGP routes).  These devices tend to have excess
   capacity, both for forwarding and routing state.

   LISP functionality can also be deployed in edge switches.  These
   devices generally have layer-2 ports facing hosts and layer-3 ports
   facing the Internet.  Spare capacity is also often available in these
   devices as well.

8.2.  Border/Edge Tunnel Routers

   Using customer-edge (CE) routers for tunnel endpoints allows the EID
   space associated with a site to be reachable via a small set of RLOCs
   assigned to the CE routers for that site.

   This offers the opposite benefit of the first-hop/last-hop tunnel
   router scenario: the number of mapping entries and network management
   touch points are reduced, allowing better scaling.

   One disadvantage is that less of the network's resources are used to
   reach host endpoints thereby centralizing the point-of-failure domain
   and creating network choke points at the CE router.

   Note that more than one CE router at a site can be configured with
   the same IP address.  In this case an RLOC is an anycast address.
   This allows resilience between the CE routers.  That is, if a CE
   router fails, traffic is automatically routed to the other routers
   using the same anycast address.  However, this comes with the
   disadvantage where the site cannot control the entrance point when
   the anycast route is advertised out from all border routers.





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8.3.  ISP Provider-Edge (PE) Tunnel Routers

   Use of ISP PE routers as tunnel endpoint routers gives an ISP control
   over the location of the egress tunnel endpoints.  That is, the ISP
   can decide if the tunnel endpoints are in the destination site (in
   either CE routers or last-hop routers within a site) or at other PE
   edges.  The advantage of this case is that two or more tunnel headers
   can be avoided.  By having the PE be the first router on the path to
   encapsulate, it can choose a TE path first, and the ETR can
   decapsulate and re-encapsulate for a tunnel to the destination end
   site.

   An obvious disadvantage is that the end site has no control over
   where its packets flow or the RLOCs used.

   As mentioned in earlier sections a combination of these scenarios is
   possible at the expense of extra packet header overhead, if both site
   and provider want control, then recursive or re-encapsulating tunnels
   are used.
































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9.  Traceroute Considerations

   When a source host in a LISP site initiates a traceroute to a
   destination host in another LISP site, it is highly desirable for it
   to see the entire path.  Since packets are encapsulated from ITR to
   ETR, the hop across the tunnel could be viewed as a single hop.
   However, LISP traceroute will provide the entire path so the user can
   see 3 distinct segments of the path from a source LISP host to a
   destination LISP host:


      Segment 1 (in source LISP site based on EIDs):

          source-host ---> first-hop ... next-hop ---> ITR

      Segment 2 (in the core network based on RLOCs):

          ITR ---> next-hop ... next-hop ---> ETR

      Segment 3 (in the destination LISP site based on EIDs):

          ETR ---> next-hop ... last-hop ---> destination-host

   For segment 1 of the path, ICMP Time Exceeded messages are returned
   in the normal matter as they are today.  The ITR performs a TTL
   decrement and test for 0 before encapsulating.  So the ITR hop is
   seen by the traceroute source has an EID address (the address of
   site-facing interface).

   For segment 2 of the path, ICMP Time Exceeded messages are returned
   to the ITR because the TTL decrement to 0 is done on the outer
   header, so the destination of the ICMP messages are to the ITR RLOC
   address, the source source RLOC address of the encapsulated
   traceroute packet.  The ITR looks inside of the ICMP payload to
   inspect the traceroute source so it can return the ICMP message to
   the address of the traceroute client as well as retaining the core
   router IP address in the ICMP message.  This is so the traceroute
   client can display the core router address (the RLOC address) in the
   traceroute output.  The ETR returns its RLOC address and responds to
   the TTL decrement to 0 like the previous core routers did.

   For segment 3, the next-hop router downstream from the ETR will be
   decrementing the TTL for the packet that was encapsulated, sent into
   the core, decapsulated by the ETR, and forwarded because it isn't the
   final destination.  If the TTL is decremented to 0, any router on the
   path to the destination of the traceroute, including the next-hop
   router or destination, will send an ICMP Time Exceeded message to the
   source EID of the traceroute client.  The ICMP message will be



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   encapsulated by the local ITR and sent back to the ETR in the
   originated traceroute source site, where the packet will be delivered
   to the host.

9.1.  IPv6 Traceroute

   IPv6 traceroute follows the procedure described above since the
   entire traceroute data packet is included in ICMP Time Exceeded
   message payload.  Therefore, only the ITR needs to pay special
   attention for forwarding ICMP messages back to the traceroute source.

9.2.  IPv4 Traceroute

   For IPv4 traceroute, we cannot follow the above procedure since IPv4
   ICMP Time Exceeded messages only include the invoking IP header and 8
   bytes that follow the IP header.  Therefore, when a core router sends
   an IPv4 Time Exceeded message to an ITR, all the ITR has in the ICMP
   payload is the encapsulated header it prepended followed by a UDP
   header.  The original invoking IP header, and therefore the identity
   of the traceroute source is lost.

   The solution we propose to solve this problem is to cache traceroute
   IPv4 headers in the ITR and to match them up with corresponding IPv4
   Time Exceeded messages received from core routers and the ETR.  The
   ITR will use a circular buffer for caching the IPv4 and UDP headers
   of traceroute packets.  It will select a 16-bit number as a key to
   find them later when the IPv4 Time Exceeded messages are received.
   When an ITR encapsulates an IPv4 traceroute packet, it will use the
   16-bit number as the UDP source port in the encapsulating header.
   When the ICMP Time Exceeded message is returned to the ITR, the UDP
   header of the encapsulating header is present in the ICMP payload
   thereby allowing the ITR to find the cached headers for the
   traceroute source.  The ITR puts the cached headers in the payload
   and sends the ICMP Time Exceeded message to the traceroute source
   retaining the source address of the original ICMP Time Exceeded
   message (a core router or the ETR of the site of the traceroute
   destination).

9.3.  Traceroute using Mixed Locators

   When either an IPv4 traceroute or IPv6 traceroute is originated and
   the ITR encapsulates it in the other address family header, you
   cannot get all 3 segments of the traceroute.  Segment 2 of the
   traceroute can not be conveyed to the traceroute source since it is
   expecting addresses from intermediate hops in the same address format
   for the type of traceroute it originated.  Therefore, in this case,
   segment 2 will make the tunnel look like one hop.  All the ITR has to
   do to make this work is to not copy the inner TTL to the outer,



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   encapsulating header's TTL when a traceroute packet is encapsulated
   using an RLOC from a different address family.  This will cause no
   TTL decrement to 0 to occur in core routers between the ITR and ETR.
















































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10.  Mobility Considerations

   There are several kinds of mobility of which only some might be of
   concern to LISP.  Essentially they are as follows.

10.1.  Site Mobility

   A site wishes to change its attachment points to the Internet, and
   its LISP Tunnel Routers will have new RLOCs when it changes upstream
   providers.  Changes in EID-RLOC mappings for sites are expected to be
   handled by configuration, outside of the LISP protocol.

10.2.  Slow Endpoint Mobility

   An individual endpoint wishes to move, but is not concerned about
   maintaining session continuity.  Renumbering is involved.  LISP can
   help with the issues surrounding renumbering [RFC4192] [LISA96] by
   decoupling the address space used by a site from the address spaces
   used by its ISPs.  [RFC4984]

10.3.  Fast Endpoint Mobility

   Fast endpoint mobility occurs when an endpoint moves relatively
   rapidly, changing its IP layer network attachment point.  Maintenance
   of session continuity is a goal.  This is where the Mobile IPv4
   [RFC3344bis] and Mobile IPv6 [RFC3775] [RFC4866] mechanisms are used,
   and primarily where interactions with LISP need to be explored.

   The problem is that as an endpoint moves, it may require changes to
   the mapping between its EID and a set of RLOCs for its new network
   location.  When this is added to the overhead of mobile IP binding
   updates, some packets might be delayed or dropped.

   In IPv4 mobility, when an endpoint is away from home, packets to it
   are encapsulated and forwarded via a home agent which resides in the
   home area the endpoint's address belongs to.  The home agent will
   encapsulate and forward packets either directly to the endpoint or to
   a foreign agent which resides where the endpoint has moved to.
   Packets from the endpoint may be sent directly to the correspondent
   node, may be sent via the foreign agent, or may be reverse-tunneled
   back to the home agent for delivery to the mobile node.  As the
   mobile node's EID or available RLOC changes, LISP EID-to-RLOC
   mappings are required for communication between the mobile node and
   the home agent, whether via foreign agent or not.  As a mobile
   endpoint changes networks, up to three LISP mapping changes may be
   required:





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   o  The mobile node moves from an old location to a new visited
      network location and notifies its home agent that it has done so.
      The Mobile IPv4 control packets the mobile node sends pass through
      one of the new visited network's ITRs, which needs a EID-RLOC
      mapping for the home agent.

   o  The home agent might not have the EID-RLOC mappings for the mobile
      node's "care-of" address or its foreign agent in the new visited
      network, in which case it will need to acquire them.

   o  When packets are sent directly to the correspondent node, it may
      be that no traffic has been sent from the new visited network to
      the correspondent node's network, and the new visited network's
      ITR will need to obtain an EID-RLOC mapping for the correspondent
      node's site.

   In addition, if the IPv4 endpoint is sending packets from the new
   visited network using its original EID, then LISP will need to
   perform a route-returnability check on the new EID-RLOC mapping for
   that EID.

   In IPv6 mobility, packets can flow directly between the mobile node
   and the correspondent node in either direction.  The mobile node uses
   its "care-of" address (EID).  In this case, the route-returnability
   check would not be needed but one more LISP mapping lookup may be
   required instead:

   o  As above, three mapping changes may be needed for the mobile node
      to communicate with its home agent and to send packets to the
      correspondent node.

   o  In addition, another mapping will be needed in the correspondent
      node's ITR, in order for the correspondent node to send packets to
      the mobile node's "care-of" address (EID) at the new network
      location.

   When both endpoints are mobile the number of potential mapping
   lookups increases accordingly.

   As a mobile node moves there are not only mobility state changes in
   the mobile node, correspondent node, and home agent, but also state
   changes in the ITRs and ETRs for at least some EID-prefixes.

   The goal is to support rapid adaptation, with little delay or packet
   loss for the entire system.  Heuristics can be added to LISP to
   reduce the number of mapping changes required and to reduce the delay
   per mapping change.  Also IP mobility can be modified to require
   fewer mapping changes.  In order to increase overall system



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   performance, there may be a need to reduce the optimization of one
   area in order to place fewer demands on another.

   In LISP, one possibility is to "glean" information.  When a packet
   arrives, the ETR could examine the EID-RLOC mapping and use that
   mapping for all outgoing traffic to that EID.  It can do this after
   performing a route-returnability check, to ensure that the new
   network location does have a internal route to that endpoint.
   However, this does not cover the case where an ITR (the node assigned
   the RLOC) at the mobile-node location has been compromised.

   Mobile IP packet exchange is designed for an environment in which all
   routing information is disseminated before packets can be forwarded.
   In order to allow the Internet to grow to support expected future
   use, we are moving to an environment where some information may have
   to be obtained after packets are in flight.  Modifications to IP
   mobility should be considered in order to optimize the behavior of
   the overall system.  Anything which decreases the number of new EID-
   RLOC mappings needed when a node moves, or maintains the validity of
   an EID-RLOC mapping for a longer time, is useful.

10.4.  Fast Network Mobility

   In addition to endpoints, a network can be mobile, possibly changing
   xTRs.  A "network" can be as small as a single router and as large as
   a whole site.  This is different from site mobility in that it is
   fast and possibly short-lived, but different from endpoint mobility
   in that a whole prefix is changing RLOCs.  However, the mechanisms
   are the same and there is no new overhead in LISP.  A map request for
   any endpoint will return a binding for the entire mobile prefix.

   If mobile networks become a more common occurrence, it may be useful
   to revisit the design of the mapping service and allow for dynamic
   updates of the database.

   The issue of interactions between mobility and LISP needs to be
   explored further.  Specific improvements to the entire system will
   depend on the details of mapping mechanisms.  Mapping mechanisms
   should be evaluated on how well they support session continuity for
   mobile nodes.

10.5.  LISP Mobile Node Mobility

   An mobile device can use the LISP infrastructure to achieve mobility
   by implementing the LISP encapsulation and decapsulation functions
   and acting as a simple ITR/ETR.  By doing this, such a "LISP mobile
   node" can use topologically-independent EID IP addresses that are not
   advertised into and do not impose a cost on the global routing



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   system.  These EIDs are maintained at the edges of the mapping system
   (in LISP Map-Servers and Map-Resolvers) and are provided on demand to
   only the correspondents of the LISP mobile node.

   Refer to the LISP Mobility Architecture specification [LISP-MN] for
   more details.













































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11.  Multicast Considerations

   A multicast group address, as defined in the original Internet
   architecture is an identifier of a grouping of topologically
   independent receiver host locations.  The address encoding itself
   does not determine the location of the receiver(s).  The multicast
   routing protocol, and the network-based state the protocol creates,
   determines where the receivers are located.

   In the context of LISP, a multicast group address is both an EID and
   a Routing Locator.  Therefore, no specific semantic or action needs
   to be taken for a destination address, as it would appear in an IP
   header.  Therefore, a group address that appears in an inner IP
   header built by a source host will be used as the destination EID.
   The outer IP header (the destination Routing Locator address),
   prepended by a LISP router, will use the same group address as the
   destination Routing Locator.

   Having said that, only the source EID and source Routing Locator
   needs to be dealt with.  Therefore, an ITR merely needs to put its
   own IP address in the source Routing Locator field when prepending
   the outer IP header.  This source Routing Locator address, like any
   other Routing Locator address MUST be globally routable.

   Therefore, an EID-to-RLOC mapping does not need to be performed by an
   ITR when a received data packet is a multicast data packet or when
   processing a source-specific Join (either by IGMPv3 or PIM).  But the
   source Routing Locator is decided by the multicast routing protocol
   in a receiver site.  That is, an EID to Routing Locator translation
   is done at control-time.

   Another approach is to have the ITR not encapsulate a multicast
   packet and allow the the host built packet to flow into the core even
   if the source address is allocated out of the EID namespace.  If the
   RPF-Vector TLV [RPFV] is used by PIM in the core, then core routers
   can RPF to the ITR (the Locator address which is injected into core
   routing) rather than the host source address (the EID address which
   is not injected into core routing).

   To avoid any EID-based multicast state in the network core, the first
   approach is chosen for LISP-Multicast.  Details for LISP-Multicast
   and Interworking with non-LISP sites is described in specification
   [MLISP].








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12.  Security Considerations

   It is believed that most of the security mechanisms will be part of
   the mapping database service when using control plane procedures for
   obtaining EID-to-RLOC mappings.  For data plane triggered mappings,
   as described in this specification, protection is provided against
   ETR spoofing by using Return- Routability mechanisms evidenced by the
   use of a 24-bit Nonce field in the LISP encapsulation header and a
   64-bit Nonce field in the LISP control message.  The nonce, coupled
   with the ITR accepting only solicited Map-Replies goes a long way
   toward providing decent authentication.

   LISP does not rely on a PKI infrastructure or a more heavy weight
   authentication system.  These systems challenge the scalability of
   LISP which was a primary design goal.

   DoS attack prevention will depend on implementations rate-limiting
   Map-Requests and Map-Replies to the control plane as well as rate-
   limiting the number of data-triggered Map-Replies.

   To deal with map-cache exhaustion attempts in an ITR/PTR, the
   implementation should consider putting a maximum cap on the number of
   entries stored with a reserve list for special or frequently accessed
   sites.  This should be a configuration policy control set by the
   network administrator who manages ITRs and PTRs.


























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13.  Prototype Plans and Status

   The operator community has requested that the IETF take a practical
   approach to solving the scaling problems associated with global
   routing state growth.  This document offers a simple solution which
   is intended for use in a pilot program to gain experience in working
   on this problem.

   The authors hope that publishing this specification will allow the
   rapid implementation of multiple vendor prototypes and deployment on
   a small scale.  Doing this will help the community:

   o  Decide whether a new EID-to-RLOC mapping database infrastructure
      is needed or if a simple, UDP-based, data-triggered approach is
      flexible and robust enough.

   o  Experiment with provider-independent assignment of EIDs while at
      the same time decreasing the size of DFZ routing tables through
      the use of topologically-aligned, provider-based RLOCs.

   o  Determine whether multiple levels of tunneling can be used by ISPs
      to achieve their Traffic Engineering goals while simultaneously
      removing the more specific routes currently injected into the
      global routing system for this purpose.

   o  Experiment with mobility to determine if both acceptable
      convergence and session continuity properties can be scalably
      implemented to support both individual device roaming and site
      service provider changes.

   Here is a rough set of milestones:

   1.  Interoperable implementations have been available since the
       beginning of 2009.  We are trying to converge on a packet format
       so implementations can converge on the -04 and later drafts.

   2.  Continue pilot deployment using LISP-ALT as the database mapping
       mechanism.

   3.  Continue prototyping and studying other database lookup schemes,
       be it DNS, DHTs, CONS, ALT, NERD, or other mechanisms.

   4.  Implement the LISP Multicast draft [MLISP].

   5.  Implement the LISP Mobile Node draft [LISP-MN].

   6.  Research more on how policy affects what gets returned in a Map-
       Reply from an ETR.



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   7.  Continue to experiment with mixed locator-sets to understand how
       LISP can help the IPv4 to IPv6 transition.

   8.  Add more robustness to locator reachability between LISP sites.

   As of this writing the following accomplishments have been achieved:

   1.   A unit- and system-tested software switching implementation has
        been completed on cisco NX-OS for this draft for both IPv4 and
        IPv6 EIDs using a mixed locator-set of IPv4 and IPv6 locators.

   2.   A unit- and system-tested software switching implementation on
        cisco NX-OS has been completed for draft [ALT].

   3.   A unit- and system-tested software switching implementation on
        cisco NX-OS has been completed for draft [INTERWORK].  Support
        for IPv4 translation is provided and PTR support for IPv4 and
        IPv6 is provided.

   4.   The cisco NX-OS implementation supports an experimental
        mechanism for slow mobility.

   5.   Dave Meyer, Vince Fuller, Darrel Lewis, Greg Shepherd, and
        Andrew Partan continue to test all the features described above
        on a dual-stack infrastructure.

   6.   Darrel Lewis and Dave Meyer have deployed both LISP translation
        and LISP PTR support in the pilot network.  Point your browser
        to http://www.lisp4.net to see translation happening in action
        so your non-LISP site can access a web server in a LISP site.

   7.   Soon http://www.lisp6.net will work where your IPv6 LISP site
        can talk to a IPv6 web server in a LISP site by using mixed
        address-family based locators.

   8.   An public domain implementation of LISP is underway.  See
        [OPENLISP] for details.

   9.   We have deployed Map-Resolvers and Map-Servers on the LISP pilot
        network to gather experience with [LISP-MS].  The first layer of
        the architecture are the xTRs which use Map-Servers for EID-
        prefix registration and Map-Resolvers for EID-to-RLOC mapping
        resolution.  The second layer are the Map-Resolvers and Map-
        Servers which connect to the ALT BGP peering infrastructure.
        And the third layer are ALT-routers which aggregate EID-prefixes
        and forward Map-Requests.





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   10.  A cisco IOS implementation is underway which currently supports
        IPv4 encapsulation and decapsulation features.

   11.  A LISP router based LIG implementation is supported, deployed,
        and used daily to debug and test the LISP pilot network.  See
        [LIG] for details.

   12.  A Linux implementation of LIG has been made available and
        supported by Dave Meyer.  It can be run on any Linux system
        which resides in either a LISP site or non-LISP site.  See [LIG]
        for details.  Public domain code can be downloaded from
        http://github.com/davidmeyer/lig/tree/master.

   13.  An experimental implementation has been written for three
        locator reachability algorithms.  Two are the Echo-Noncing and
        RLOC-Probing algorithms which are documented in this
        specification.  The third is called TCP-counts which will be
        documented in future drafts.

   14.  The LISP pilot network has been converted from using MD5 HMAC
        authentication for Map-Register messages to SHA-1 HMAC
        authentication.  ETRs send with SHA-1 but Map-Servers can
        received from either for compatibility purposes.

   If interested in writing a LISP implementation, testing any of the
   LISP implementations, or want to be part of the LISP pilot program,
   please contact lisp@ietf.org.
























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14.  References

14.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              November 1990.

   [RFC1498]  Saltzer, J., "On the Naming and Binding of Network
              Destinations", RFC 1498, August 1993.

   [RFC1955]  Hinden, R., "New Scheme for Internet Routing and
              Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2404]  Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
              ESP and AH", RFC 2404, November 1998.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, September 2001.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4423]  Moskowitz, R. and P. Nikander, "Host Identity Protocol
              (HIP) Architecture", RFC 4423, May 2006.

   [RFC4634]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and HMAC-SHA)", RFC 4634, July 2006.



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   [RFC4866]  Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
              Optimization for Mobile IPv6", RFC 4866, May 2007.

   [RFC4984]  Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
              Workshop on Routing and Addressing", RFC 4984,
              September 2007.

   [UDP-TUNNELS]
              Eubanks, M. and P. Chimento, "UDP Checksums for Tunneled
              Packets"", draft-eubanks-chimento-6man-00.txt (work in
              progress), February 2009.

14.2.  Informative References

   [AFI]      IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
              NUMBERS http://www.iana.org/numbers.html, Febuary 2007.

   [ALT]      Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
              Alternative Topology (LISP-ALT)",
              draft-ietf-lisp-alt-01.txt (work in progress), May 2009.

   [APT]      Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
              L. Zhang, "APT: A Practical Transit Mapping Service",
              draft-jen-apt-01.txt (work in progress), November 2007.

   [CHIAPPA]  Chiappa, J., "Endpoints and Endpoint names: A Proposed
              Enhancement to the Internet Architecture", Internet-
              Draft http://www.chiappa.net/~jnc/tech/endpoints.txt,
              1999.

   [CONS]     Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
              Content distribution Overlay Network  Service for LISP",
              draft-meyer-lisp-cons-03.txt (work in progress),
              November 2007.

   [DHTs]     Ratnasamy, S., Shenker, S., and I. Stoica, "Routing
              Algorithms for DHTs: Some Open Questions", PDF
              file http://www.cs.rice.edu/Conferences/IPTPS02/174.pdf.

   [EMACS]    Brim, S., Farinacci, D., Meyer, D., and J. Curran, "EID
              Mappings Multicast Across Cooperating Systems for LISP",
              draft-curran-lisp-emacs-00.txt (work in progress),
              November 2007.

   [GSE]      "GSE - An Alternate Addressing Architecture for  IPv6",
              draft-ietf-ipngwg-gseaddr-00.txt (work in progress), 1997.

   [INTERWORK]



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              Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking LISP with IPv4 and IPv6",
              draft-ietf-lisp-interworking-00.txt (work in progress),
              January 2009.

   [LIG]      Farinacci, D. and D. Meyer, "LISP Internet Groper (LIG)",
              draft-farinacci-lisp-lig-01.txt (work in progress),
              May 2009.

   [LISA96]   Lear, E., Katinsky, J., Coffin, J., and D. Tharp,
              "Renumbering: Threat or Menace?", Usenix , September 1996.

   [LISP-MAIN]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-farinacci-lisp-12.txt (work in progress),
              March 2009.

   [LISP-MN]  Farinacci, D., Fuller, V., Lewis, D., and D. Meyer, "LISP
              Mobility Architecture", draft-meyer-lisp-mn-00.txt (work
              in progress), July 2009.

   [LISP-MS]  Farinacci, D. and V. Fuller, "LISP Map Server",
              draft-ietf-lisp-ms-03.txt (work in progress),
              September 2009.

   [LISP1]    Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
              "Locator/ID Separation Protocol (LISP1) [Routable  ID
              Version]",
              Slide-set http://www.dinof.net/~dino/ietf/lisp1.ppt,
              October 2006.

   [LISP2]    Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
              "Locator/ID Separation Protocol (LISP2) [DNS-based
              Version]",
              Slide-set http://www.dinof.net/~dino/ietf/lisp2.ppt,
              November 2006.

   [LISPDHT]  Mathy, L., Iannone, L., and O. Bonaventure, "LISP-DHT:
              Towards a DHT to map identifiers onto locators",
              draft-mathy-lisp-dht-00.txt (work in progress),
              February 2008.

   [LOC-ID-ARCH]
              Meyer, D. and D. Lewis, "Architectural Implications of
              Locator/ID  Separation",
              draft-meyer-loc-id-implications-01.txt (work in progress),
              Januaryr 2009.



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   [MLISP]    Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas,
              "LISP for Multicast Environments",
              draft-ietf-lisp-multicast-02.txt (work in progress),
              September 2009.

   [NERD]     Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
              draft-lear-lisp-nerd-04.txt (work in progress),
              April 2008.

   [OPENLISP]
              Iannone, L. and O. Bonaventure, "OpenLISP Implementation
              Report", draft-iannone-openlisp-implementation-01.txt
              (work in progress), July 2008.

   [RADIR]    Narten, T., "Routing and Addressing Problem Statement",
              draft-narten-radir-problem-statement-00.txt (work in
              progress), July 2007.

   [RFC3344bis]
              Perkins, C., "IP Mobility Support for IPv4, revised",
              draft-ietf-mip4-rfc3344bis-05 (work in progress),
              July 2007.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.

   [RPFV]     Wijnands, IJ., Boers, A., and E. Rosen, "The RPF Vector
              TLV", draft-ietf-pim-rpf-vector-08.txt (work in progress),
              January 2009.

   [RPMD]     Handley, M., Huici, F., and A. Greenhalgh, "RPMD: Protocol
              for Routing Protocol Meta-data  Dissemination",
              draft-handley-p2ppush-unpublished-2007726.txt (work in
              progress), July 2007.

   [SHIM6]    Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim
              protocol", draft-ietf-shim6-proto-06.txt (work in
              progress), October 2006.












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Appendix A.  Acknowledgments

   An initial thank you goes to Dave Oran for planting the seeds for the
   initial ideas for LISP.  His consultation continues to provide value
   to the LISP authors.

   A special and appreciative thank you goes to Noel Chiappa for
   providing architectural impetus over the past decades on separation
   of location and identity, as well as detailed review of the LISP
   architecture and documents, coupled with enthusiasm for making LISP a
   practical and incremental transition for the Internet.

   The authors would like to gratefully acknowledge many people who have
   contributed discussion and ideas to the making of this proposal.
   They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller,
   Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston,
   David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley,
   Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler,
   Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi
   Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Roger
   Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van Beijnum, Roland
   Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien Saucez, Damian
   Lezama, Attilla De Groot, Parantap Lahiri, David Black, Roque
   Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin, Margaret
   Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, and Jari
   Arkko.

   In particular, we would like to thank Dave Meyer for his clever
   suggestion for the name "LISP". ;-)

   This work originated in the Routing Research Group (RRG) of the IRTF.
   The individual submission [LISP-MAIN] was converted into this IETF
   LISP working group draft.


















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Appendix B.  Document Change Log

B.1.  Changes to draft-ietf-lisp-05.txt

   o  Posted September 2009.

   o  Added this Document Change Log appendix.

   o  Added section indicating that encapsulated Map-Requests must use
      destination UDP port 4342.

   o  Don't use AH in Map-Registers.  Put key-id, auth-length, and auth-
      data in Map-Register payload.

   o  Added Jari to acknowledgment section.

   o  State the source-EID is set to 0 when using Map-Requests to
      refresh or RLOC-probe.

   o  Make more clear what source-RLOC should be for a Map-Request.

   o  The LISP-CONS authors thought that the Type definitions for CONS
      should be removed from this specification.

   o  Removed nonce from Map-Register message, it wasn't used so no need
      for it.

   o  Clarify what to do for unspecified Action bits for negative Map-
      Replies.  Since No Action is a drop, make value 0 Drop.

B.2.  Changes to draft-ietf-lisp-04.txt

   o  Posted September 2009.

   o  How do deal with record count greater than 1 for a Map-Request.
      Damien and Joel comment.  Joel suggests: 1) Specify that senders
      compliant with the current document will always set the count to
      1, and note that the count is included for future extensibility.
      2) Specify what a receiver compliant with the draft should do if
      it receives a request with a count greater than 1.  Presumably, it
      should send some error back?

   o  Add Fred Templin in ack section.

   o  Add Margaret and Sam to the ack section for their great comments.

   o  Say more about LAGs in the UDP section per Sam Hartman's comment.




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   o  Sam wants to use MAY instead of SHOULD for ignoring checksums on
      ETR.  From the mailing list: "You'd need to word it as an ITR MAY
      send a zero checksum, an ETR MUST accept a 0 checksum and MAY
      ignore the checksum completely.  And of course we'd need to
      confirm that can actually be implemented.  In particular, hardware
      that verifies UDP checksums on receive needs to be checked to make
      sure it permits 0 checksums."

   o  Margaret wants a reference to
      http://www.ietf.org/id/draft-eubanks-chimento-6man-00.txt.

   o  Fix description in Map-Request section.  Where we describe Map-
      Reply Record, change "R-bit" to "M-bit".

   o  Add the mobility bit to Map-Replies.  So PTRs don't probe so often
      for MNs but often enough to get mapping updates.

   o  Indicate SHA1 can be used as well for Map-Registers.

   o  More Fred comments on MTU handling.

   o  Isidor comment about specing better periodic Map-Registers.  Will
      be fixed in draft-ietf-lisp-ms-02.txt.

   o  Margaret's comment on gleaning: "The current specification does
      not make it clear how long gleaned map entries should be retained
      in the cache, nor does it make it clear how/ when they will be
      validated.  The LISP spec should, at the very least, include a
      (short) default lifetime for gleaned entries, require that they be
      validated within a short period of time, and state that a new
      gleaned entry should never overwrite an entry that was obtained
      from the mapping system.  The security implications of storing
      "gleaned" entries should also be explored in detail."

   o  Add section on RLOC-probing per working group feedback.

   o  Change "loc-reach-bits" to "loc-status-bits" per comment from
      Noel.

   o  Remove SMR-bit from data-plane.  Dino prefers to have it in the
      control plane only.

   o  Change LISP header to allow a "Research Bit" so the Nonce and LSB
      fields can be turned off and used for another future purpose.  For
      Luigi et al versioning convergence.

   o  Add a N-bit to the data header suggested by Noel.  Then the nonce
      field could be used when N is not 1.



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   o  Clarify that when E-bit is 0, the nonce field can be an echoed
      nonce or a random nonce.  Comment from Jesper.

   o  Indicate when doing data-gleaning that a verifying Map-Request is
      sent to the source-EID of the gleaned data packet so we can avoid
      map-cache corruption by a 3rd party.  Comment from Pedro.

   o  Indicate that a verifying Map-Request, for accepting mapping data,
      should be sent over the the ALT (or to the EID).

   o  Reference IPsec RFC 4302.  Comment from Sam and Brian Weis.

   o  Put E-bit in Map-Reply to tell ITRs that the ETR supports echo-
      noncing.  Comment by Pedro and Dino.

   o  Jesper made a comment to loosen the language about requiring the
      copy of inner TTL to outer TTL since the text to get mixed-AF
      traceroute to work would violate the "MUST" clause.  Changed from
      MUST to SHOULD in section 5.3.

B.3.  Changes to draft-ietf-lisp-03.txt

   o  Posted July 2009.

   o  Removed loc-reach-bits longword from control packets per Damien
      comment.

   o  Clarifications in MTU text from Roque.

   o  Added text to indicate that the locator-set be sorted by locator
      address from Isidor.

   o  Clarification text from JohnZ in Echo-Nonce section.

B.4.  Changes to draft-ietf-lisp-02.txt

   o  Posted July 2009.

   o  Encapsulation packet format change to add E-bit and make loc-
      reach-bits 32-bits in length.

   o  Added Echo-Nonce Algorithm section.

   o  Clarification how ECN bits are copied.

   o  Moved S-bit in Map-Request.





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   o  Added P-bit in Map-Request and Map-Reply messages to anticipate
      RLOC-Probe Algorithm.

   o  Added to Mobility section to reference draft-meyer-lisp-mn-00.txt.

B.5.  Changes to draft-ietf-lisp-01.txt

   o  Posted 2 days after draft-ietf-lisp-00.txt in May 2009.

   o  Defined LEID to be a "LISP EID".

   o  Indicate encapsulation use IPv4 DF=0.

   o  Added negative Map-Reply messages with drop, native-forward, and
      send-map-request actions.

   o  Added Proxy-Map-Reply bit to Map-Register.

B.6.  Changes to draft-ietf-lisp-00.txt

   o  Posted May 2009.

   o  Rename of draft-farinacci-lisp-12.txt.

   o  Acknowledgment to RRG.


























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Authors' Addresses

   Dino Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: dino@cisco.com


   Vince Fuller
   cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: vaf@cisco.com


   Dave Meyer
   cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: dmm@cisco.com


   Darrel Lewis
   cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: darlewis@cisco.com















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