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Network Working Group                                       D. Farinacci
Internet-Draft                                                 V. Fuller
Intended status: Experimental                                    D. Oran
Expires: April 13, 2009                                         D. Meyer
                                                                 S. Brim
                                                           cisco Systems
                                                        October 10, 2008


                 Locator/ID Separation Protocol (LISP)
                      draft-farinacci-lisp-09.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on April 13, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008).











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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.







































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Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  8
   4.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 13
   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  . . . . . . . . . 20
   6.  EID-to-RLOC Mapping  . . . . . . . . . . . . . . . . . . . . . 22
     6.1.  Control Plane Packet Format  . . . . . . . . . . . . . . . 22
       6.1.1.  LISP Packet Type Allocations . . . . . . . . . . . . . 24
       6.1.2.  Map-Request Message Format . . . . . . . . . . . . . . 24
       6.1.3.  EID-to-RLOC UDP Map-Request Message  . . . . . . . . . 26
       6.1.4.  Map-Reply Message Format . . . . . . . . . . . . . . . 26
       6.1.5.  EID-to-RLOC UDP Map-Reply Message  . . . . . . . . . . 29
     6.2.  Routing Locator Selection  . . . . . . . . . . . . . . . . 29
     6.3.  Routing Locator Reachability . . . . . . . . . . . . . . . 30
     6.4.  Routing Locator Hashing  . . . . . . . . . . . . . . . . . 32
     6.5.  Changing the Contents of EID-to-RLOC Mappings  . . . . . . 33
       6.5.1.  Clock Sweep  . . . . . . . . . . . . . . . . . . . . . 34
       6.5.2.  Solicit-Map-Request (SMR)  . . . . . . . . . . . . . . 34
   7.  Router Performance Considerations  . . . . . . . . . . . . . . 36
   8.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 37
     8.1.  First-hop/Last-hop Tunnel Routers  . . . . . . . . . . . . 38
     8.2.  Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 38
     8.3.  ISP Provider-Edge (PE) Tunnel Routers  . . . . . . . . . . 39
   9.  Mobility Considerations  . . . . . . . . . . . . . . . . . . . 40
     9.1.  Site Mobility  . . . . . . . . . . . . . . . . . . . . . . 40
     9.2.  Slow Endpoint Mobility . . . . . . . . . . . . . . . . . . 40
     9.3.  Fast Endpoint Mobility . . . . . . . . . . . . . . . . . . 40
     9.4.  Fast Network Mobility  . . . . . . . . . . . . . . . . . . 42
   10. Multicast Considerations . . . . . . . . . . . . . . . . . . . 43
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 44
   12. Prototype Plans and Status . . . . . . . . . . . . . . . . . . 45
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 47
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 47
     13.2. Informative References . . . . . . . . . . . . . . . . . . 47
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 50
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 51
   Intellectual Property and Copyright Statements . . . . . . . . . . 52







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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.  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.

   3.  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).

   4.  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 document decouples the
   mechanism used for forwarding packets from that used to determine EID
   to RLOC mappings.  This work is in response to and intended to
   address the problem statement that came out of the 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 should facilitate incremental deployment of the



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   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.  Minimize required changes to Internet infrastructure.

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

   3.  Be incrementally deployable.

   4.  Require no router hardware changes.

   5.  Minimize router software changes.

   6.  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:

   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



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      [CONS], [ALT], [RPMD], [NERD], and [APT].

   This document will focus on LISP 1 and LISP 1.5, both of which rely
   on a router-based distributed cache and database for EID-to-RLOC
   mappings.  The LISP 2 and LISP 3 mechanisms, which require separate
   EID-to-RLOC infrastructure, will be documented elsewhere.













































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3.  Definition of Terms

   Provider Independent (PI) Addresses:   an address block assigned from
      a pool that is not associated with any 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.

   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



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      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 it's 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
      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.






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   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 database 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
      "database", the cache is dynamic, local, 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 staticly 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 prepend 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
      staticly configured.

   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.







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   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.

   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.  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
   addresses (RLOCs) in the IP header.

   This design introduces "Tunnel Routers", which prepend 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.  Keep in mind that an EID is only routable within the scope
      of a site.  A typical BGP configuration might demonstrate this
      "hybrid" EID/RLOC 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



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      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 pre-pended to packets by a transit
   router (i.e.  TE-ITR) when re-routing of the end-to-end 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
   Locator/ID 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.

4.1.  Packet Flow Sequence

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



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   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 each of the site's attached service provider
      address blocks.

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

   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 IP/IPv6 packet is built using the EIDs in the IP/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 IP/IPv6 address.  The
       destination EID from the original packet header is used as the
       destination IP/IPv6 in the prepended LISP header.  Subsequent
       packets will be sent using the same LISP header 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.

   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 egress router and is addressed to
       the source RLOC from the LISP header of the original packet (this
       is the ITR).  The source RLOC in the IP header of the UDP message
       is one of the ETR's RLOCs (one of the RLOCs that is embedded in
       the UDP payload).

   5.  The ITR receives the UDP Map-Reply message, parses the message
       (to check for format validity) and stores the EID-to-RLOC



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       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 UDP Map-Reply.

   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 an
   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 one simple scheme is 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           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |S|M|                   Locator Reach Bits                      |
 LISP  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                             Nonce                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |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



       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        | Next Header=17|   Hop Limit   |
  /    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
 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           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |S|M|                   Locator Reach Bits                      |
 LISP  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                             Nonce                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        |  Next Header  |   Hop Limit   |
  /    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
 I     +                                                               +
 n     |                                                               |
 n     +                          Source EID                           +
 e     |                                                               |
 r     +                                                               +
       |                                                               |
 H     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 d     |                                                               |
 r     +                                                               +
       |                                                               |



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  \    +                        Destination EID                        +
   \   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.3.  Tunnel Header Field Descriptions

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

   OH 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].

   UDP Header:  contains a random source port allocated by the ITR when
      encapsulating a packet.  Alternatively, see Section 6.4 for a
      suggested hash algorithm to 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 field MUST be transmitted as 0 and ignored
      on receipt by the ETR.  Note, even when the UDP checksum is
      transmitted as 0 an intervening NAT device can recalculate the
      checksum and rewrite the UDP checksum field to non-zero.  For
      performance reasons, the ETR MUST ignore the checksum and MUST not
      do a checksum computation.

   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
      headers are used.  The UDP header length is 8 bytes.  The LISP
      header length is 8 bytes when no loc-reach-bit header extensions
      are used.

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

   LISP Locator Reach Bits:  in the LISP header are set by an ITR to
      indicate to an ETR the reachability 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
      Reach Bits are numbered from 0 to n-1 from the right significant
      bit of the 30-bit field.  When a bit is set to 1, the ITR is
      indicating to the ETR the RLOC associated with the bit ordinal is
      reachable.  See Section 6.3 for details on how an ITR can



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      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 Reach Bits
      setting in an encapsulated packet MUST reflect the mapping for the
      EID-prefix that the inner-header source EID address matches.  When
      the M bit is set, an additional 32-bit locator reachability field
      follows, which contains an M-bit field and 31 locator reachability
      bits.  The M-bit may be set for further extension (and so on).
      This extension mechanism allows an EID to be mapped to an
      arbitrary number of RLOCs, subject only to the maximum number of
      32-bit fields that can fit into the response packet.  For
      practical purposes, a future version of this specification will
      likely set a limit on the number of these fields.

   LISP Nonce:  is a 32-bit value that is randomly generated by an ITR.
      It is used to test route-returnability when xTRs exchange
      encapsulated data packets with the SMR bit set, Data-Probe, Map-
      Request, or Map-Reply messages.

   When doing Recursive Tunneling:

   o  The OH header Time to Live field (or Hop Limit field, in case of
      IPv6) MUST be copied from the IH header Time to Live field.

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

   When doing Re-encapsulated Tunneling:

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

   o  The new OH header Type of Service field SHOULD be copied from the
      stripped OH header Type of Service field.

   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.

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 a simple and stateless
   mechanism to deal with large packets.  The mechanism is described as
   follows:




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   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 pre-pended 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).

   This specification recommends that L be defined as 1500.




















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6.  EID-to-RLOC Mapping

6.1.  Control Plane Packet Format

   When LISP 1 or LISP 1.5 is used, new UDP packet types encode the 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                          |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version| Traffic Class |           Flow Label                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Payload Length        | Next Header=17|   Hop Limit   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                     Source Routing Locator                    +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                  Destination Routing Locator                  +



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       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |           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-CONS Open Message:          8    b'1000'
       LISP-CONS Push-Add Message:      9    b'1001'
       LISP-CONS Push-Delete Message:   10   b'1010'
       LISP-CONS Uneachable Message:    11   b'1011'


6.1.2.  Map-Request Message Format



       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S|M|                   Locator Reach Bits                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             Nonce                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=1 |A|R|            Reserved               | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         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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   S: This is the SMR bit.  See Section 6.5.2 for details.

   Locator Reach Bits:  Refer to Section 5.3.

   Nonce:  A 4-byte random value created by the sender of the Map-
      Request.

   Type:   1 (Map-Request)

   A: This is an authoritative bit, which is set to 0 for UDP-based Map-
      Requests sent by an ITR.  See other control-specific documents
      [CONS] for TCP-based Map-Requests.

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

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

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

   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.

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

   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.

   Map-Reply Record  When the R 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.







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   Mapping Protocol Data:  See [CONS] or [ALT] for details.

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.  This is performed by using the RLOC as the
   destination address for Map-Request message with a randomly allocated
   source UDP port number and 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 MUST be rate-limited.  It is recommended that a Map-
   Request for the same EID-prefix be sent no more than once per second.

6.1.4.  Map-Reply Message Format



       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |x|M|                   Locator Reach Bits                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             Nonce                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=2 |              Reserved                 | Record Count  |
+----> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      |                          Record  TTL                          |
|      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R      | Locator Count | EID mask-len  |A|        Reserved             |
e      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
c      |           Reserved            |            EID-AFI            |
o      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
r      |                          EID-prefix                           |
d      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     /|    Priority   |    Weight     |  M Priority   |   M Weight    |
|    / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Loc |           Unused Flags      |R|           Loc-AFI             |
|    \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     \|                             Locator                           |
+--->  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Mapping Protocol Data                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Packet field descriptions:






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

   Locator Reach Bits:  Refer to Section 5.3.  When there are multiple
      records in the Map-Reply message, this field is set to 0 and the
      R-bit for each Locator record within each mapping record is used
      to determine the locator reachability.

   Nonce:  A 4-byte value set in a Data-Probe packet or a Map-Request
      that is echoed here in the Map-Reply.

   Type:   2 (Map-Reply)

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

   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.  If the
      record count is not 1 then the Locator Reach Bits field MUST be 0.

   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.

   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.

   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



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      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.

   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.  When there is a single
      mapping record in the message, the R-bit for each locator must
      have a consistent setting with the bitfield setting of the 'Loc
      Reach Bits' field in the early part of the header.  When there are
      multiple mapping records in the message, the 'Loc Reach Bits'
      field is set to 0.

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

   Mapping Protocol Data:  See [CONS] or [ALT] for details.






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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.

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.




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   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
      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.

   RLOCs that appear in EID-to-RLOC Map-Reply messages are considered
   reachable.  The Map-Reply and the database mapping service does not
   provide any reachability status for Locators.  This is done outside
   of the mapping service.  See next section for details.

6.3.  Routing Locator Reachability

   There are 4 methods for determining when a Locator is either
   reachable or has become unreachable:

   1.  Locator reachability is determined by an ETR by examining the
       Loc-Reach-Bits from a LISP header of a encapsulated data packet
       which is provided by an ITR when an ITR encapsulates data.



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   2.  Locator unreachability is determined by an ITR by receiving ICMP
       Network or Host Unreachable messages.

   3.  ETR unreachability is determined when a host sends an ICMP Port
       Unreachable message.

   4.  Locator reachability is determined by receiving a Map-Reply
       message from a ETR's Locator address in response to a previously
       sent Map-Request.

   When determining Locator reachability by examining the Loc-Reach-Bits
   from the LISP encapsulate data packet, an ETR will receive up to date
   status from the ITR closest to the Locators at the source site.  The
   ITRs at the source site can determine reachability when running their
   IGP at the site.  When the ITRs are deployed on CE routers, typically
   a default route is injected into the site's IGP from each of the
   ITRs.  If an ITR goes down, the CE-PE link goes down, or the PE
   router goes down, the CE router withdraws the default route.  This
   allows the other ITRs at the site to determine one of the Locators
   has gone unreachable.

   The Locators listed in a Map-Reply are numbered with ordinals 0 to
   n-1.  The Loc-Reach-Bits in a LISP Data Message are numbered from 0
   to n-1 starting with the least significant bit numbered as 0.  So,
   for example, if the ITR with locator listed as the 3rd Locator
   position in the Map-Reply goes down, all other ITRs at the site will
   have the 3rd bit from the right cleared (the bit that corresponds to
   ordinal 2).

   When an ETR decapsulates a packet, it will look for a change in the
   Loc-Reach-Bits value.  When a bit goes from 1 to 0, the ETR will
   refrain from encapsulating packets to the Locator that has just gone
   unreachable.  It can start using the Locator again when the bit that
   corresponds to the Locator goes from 0 to 1.  Loc-Reach-Bits are
   associated with a locator-set per EID-prefix.  Therefore, when a
   locator becomes unreachable, the loc-reach-bit that corresponds to
   that locator's 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 a stub links 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



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   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.

   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.

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 or UDP port
       numbers and the IP protocol number field or IPv6 next-protocol
       fields of a packet a host originates from within a LISP site.

   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.




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   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.

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-reach-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-reach-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-reach-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-reach-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.



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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:

   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 an encapsulated data packet
   (and a Map-Request message).  When an ETR at a remote site
   decapsulates a data packet that has the SMR bit set, it can tell that
   a new Map-Request message is being solicited.  Both the xTR that
   sends the SMR message and the site that acts on the SMR message MUST
   be rate-limited.




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   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 ITRs at the site
       begin to set the SMR bit in packets they encapsulate to the sites
       they communicate with.

   2.  A remote xTR which decapsulates a packet with the SMR bit set
       will schedule sending a Map-Request message to the source locator
       address of the encapsulated packet.  The nonce in the Map-Request
       is copied from the nonce in the encapsulated data packet that has
       the SMR bit set.

   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-reach-bits are reflective of the new mapping for packets
       going to the remote site.
























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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.  Mobility Considerations

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

9.1.  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.

9.2.  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]

9.3.  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.

9.4.  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.











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10.  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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11.  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 4-byte Nonce field in the LISP encapsulation header.  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.

































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12.  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.  This draft will be the draft for interoperable implementations to
       code against.  Interoperable implementations will be ready Fall
       of 2008.

   2.  Continue pilot deployment summer of 2008 using LISP-ALT as the
       database mapping mechanism.

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

   4.  Implement the LISP Multicast draft [MLISP].

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





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

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

   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-interest@lists.civil-tongue.net







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13.  References

13.1.  Normative References

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

   [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.

   [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.

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

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

   [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.

13.2.  Informative References

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

   [ALT]      Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative
              Topology (LISP-ALT)", draft-fuller-lisp-alt-03.txt (work
              in progress), April 2008.



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   [APT]      Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
              L. Zhang, "APT: A Practical Transit Mapping Service",
              draft-jen-apt-00.txt (work in progress), July 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.

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

   [INTERWORK]
              Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP
              with IPv4 and IPv6", draft-lewis-lisp-interworking-01.txt
              (work in progress), July 2008.

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

   [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.

   [MLISP]    Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas,
              "LISP for Multicast Environments",



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              draft-farinacci-lisp-multicast-00.txt (work in progress),
              April 2008.

   [NERD]     Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
              draft-lear-lisp-nerd-02.txt (work in progress),
              January 2008.

   [OPENLISP]
              Iannone, L. and O. Bonaventure, "OpenLISP Implementation
              Report", draft-iannone-openlisp-implementation-00.txt
              (work in progress), February 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-03.txt (work in progress),
              October 2006.

   [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

   The authors would like to gratefully acknowledge many people who have
   contributed discussion and ideas to the making of this proposal.
   They include Jason Schiller, Lixia Zhang, Dorian Kim, Peter
   Schoenmaker, Darrel Lewis, 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, John
   Zwiebel, Ran Atkinson, Stig Venaas, Iljitsch van Beijnum, Roland
   Bless, Andrew Partan, Dana Blair, Bill Lynch, Marc Woolward, Damien
   Saucez, and Damian Lezama.

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



































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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 Oran
   cisco Systems
   7 Ladyslipper Lane
   Acton, MA
   USA

   Email: oran@cisco.com


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

   Email: dmm@cisco.com


   Scott Brim
   cisco Systems
   170 Tasman Drive
   San Jose, CA
   USA

   Email: sbrim@cisco.com






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Full Copyright Statement

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   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
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