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Versions: (draft-farinacci-lisp-rfc6830bis) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18

Network Working Group                                       D. Farinacci
Internet-Draft                                                 V. Fuller
Obsoletes: 6830 (if approved)                                   D. Meyer
Intended status: Standards Track                                D. Lewis
Expires: March 21, 2019                                    Cisco Systems
                                                       A. Cabellos (Ed.)
                                                       UPC/BarcelonaTech
                                                      September 17, 2018


               The Locator/ID Separation Protocol (LISP)
                     draft-ietf-lisp-rfc6830bis-18

Abstract

   This document describes the Data-Plane protocol for the Locator/ID
   Separation Protocol (LISP).  LISP defines two namespaces, End-point
   Identifiers (EIDs) that identify end-hosts and Routing Locators
   (RLOCs) that identify network attachment points.  With this, LISP
   effectively separates control from data, and allows routers to create
   overlay networks.  LISP-capable routers exchange encapsulated packets
   according to EID-to-RLOC mappings stored in a local Map-Cache.

   LISP requires no change to either host protocol stacks or to underlay
   routers and offers Traffic Engineering, multihoming and mobility,
   among other features.

   This document obsoletes RFC 6830.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 21, 2019.






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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   4
   3.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   4
   4.  Basic Overview  . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Packet Flow Sequence  . . . . . . . . . . . . . . . . . .  10
   5.  LISP Encapsulation Details  . . . . . . . . . . . . . . . . .  12
     5.1.  LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . .  13
     5.2.  LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . .  14
     5.3.  Tunnel Header Field Descriptions  . . . . . . . . . . . .  15
   6.  LISP EID-to-RLOC Map-Cache  . . . . . . . . . . . . . . . . .  20
   7.  Dealing with Large Encapsulated Packets . . . . . . . . . . .  20
     7.1.  A Stateless Solution to MTU Handling  . . . . . . . . . .  21
     7.2.  A Stateful Solution to MTU Handling . . . . . . . . . . .  22
   8.  Using Virtualization and Segmentation with LISP . . . . . . .  22
   9.  Routing Locator Selection . . . . . . . . . . . . . . . . . .  23
   10. Routing Locator Reachability  . . . . . . . . . . . . . . . .  25
     10.1.  Echo Nonce Algorithm . . . . . . . . . . . . . . . . . .  26
   11. EID Reachability within a LISP Site . . . . . . . . . . . . .  27
   12. Routing Locator Hashing . . . . . . . . . . . . . . . . . . .  28
   13. Changing the Contents of EID-to-RLOC Mappings . . . . . . . .  29
     13.1.  Database Map-Versioning  . . . . . . . . . . . . . . . .  30
   14. Multicast Considerations  . . . . . . . . . . . . . . . . . .  31
   15. Router Performance Considerations . . . . . . . . . . . . . .  31
   16. Security Considerations . . . . . . . . . . . . . . . . . . .  32
   17. Network Management Considerations . . . . . . . . . . . . . .  33
   18. Changes since RFC 6830  . . . . . . . . . . . . . . . . . . .  33
   19. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
     19.1.  LISP UDP Port Numbers  . . . . . . . . . . . . . . . . .  34
   20. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     20.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     20.2.  Informative References . . . . . . . . . . . . . . . . .  35



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   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  39
   Appendix B.  Document Change Log  . . . . . . . . . . . . . . . .  39
     B.1.  Changes to draft-ietf-lisp-rfc6830bis-18  . . . . . . . .  40
     B.2.  Changes to draft-ietf-lisp-rfc6830bis-17  . . . . . . . .  40
     B.3.  Changes to draft-ietf-lisp-rfc6830bis-16  . . . . . . . .  40
     B.4.  Changes to draft-ietf-lisp-rfc6830bis-15  . . . . . . . .  40
     B.5.  Changes to draft-ietf-lisp-rfc6830bis-14  . . . . . . . .  40
     B.6.  Changes to draft-ietf-lisp-rfc6830bis-13  . . . . . . . .  40
     B.7.  Changes to draft-ietf-lisp-rfc6830bis-12  . . . . . . . .  41
     B.8.  Changes to draft-ietf-lisp-rfc6830bis-11  . . . . . . . .  41
     B.9.  Changes to draft-ietf-lisp-rfc6830bis-10  . . . . . . . .  41
     B.10. Changes to draft-ietf-lisp-rfc6830bis-09  . . . . . . . .  41
     B.11. Changes to draft-ietf-lisp-rfc6830bis-08  . . . . . . . .  42
     B.12. Changes to draft-ietf-lisp-rfc6830bis-07  . . . . . . . .  42
     B.13. Changes to draft-ietf-lisp-rfc6830bis-06  . . . . . . . .  42
     B.14. Changes to draft-ietf-lisp-rfc6830bis-05  . . . . . . . .  42
     B.15. Changes to draft-ietf-lisp-rfc6830bis-04  . . . . . . . .  43
     B.16. Changes to draft-ietf-lisp-rfc6830bis-03  . . . . . . . .  43
     B.17. Changes to draft-ietf-lisp-rfc6830bis-02  . . . . . . . .  43
     B.18. Changes to draft-ietf-lisp-rfc6830bis-01  . . . . . . . .  43
     B.19. Changes to draft-ietf-lisp-rfc6830bis-00  . . . . . . . .  43
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  43

1.  Introduction

   This document describes the Locator/Identifier Separation Protocol
   (LISP).  LISP is an encapsulation protocol built around the
   fundamental idea of separating the topological location of a network
   attachment point from the node's identity [CHIAPPA].  As a result
   LISP creates two namespaces: Endpoint Identifiers (EIDs), that are
   used to identify end-hosts (e.g., nodes or Virtual Machines) and
   routable Routing Locators (RLOCs), used to identify network
   attachment points.  LISP then defines functions for mapping between
   the two namespaces and for encapsulating traffic originated by
   devices using non-routable EIDs for transport across a network
   infrastructure that routes and forwards using RLOCs.  LISP
   encapsulation uses a dynamic form of tunneling where no static
   provisioning is required or necessary.

   LISP is an overlay protocol that separates control from Data-Plane,
   this document specifies the Data-Plane, how LISP-capable routers
   (Tunnel Routers) exchange packets by encapsulating them to the
   appropriate location.  Tunnel routers are equipped with a cache,
   called Map-Cache, that contains EID-to-RLOC mappings.  The Map-Cache
   is populated using the LISP Control-Plane protocol
   [I-D.ietf-lisp-rfc6833bis].





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   LISP does not require changes to either host protocol stack or to
   underlay routers.  By separating the EID from the RLOC space, LISP
   offers native Traffic Engineering, multihoming and mobility, among
   other features.

   Creation of LISP was initially motivated by discussions during the
   IAB-sponsored Routing and Addressing Workshop held in Amsterdam in
   October 2006 (see [RFC4984]).

   This document specifies the LISP Data-Plane encapsulation and other
   LISP forwarding node functionality while [I-D.ietf-lisp-rfc6833bis]
   specifies the LISP control plane.  LISP deployment guidelines can be
   found in [RFC7215] and [RFC6835] describes considerations for network
   operational management.  Finally, [I-D.ietf-lisp-introduction]
   describes the LISP architecture.

   This document obsoletes RFC 6830.

2.  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] and
   [RFC8174].

3.  Definition of Terms

   Address Family Identifier (AFI):   AFI is a term used to describe an
      address encoding in a packet.  An address family that pertains to
      the Data-Plane.  See [AFN] and [RFC3232] for details.  An AFI
      value of 0 used in this specification indicates an unspecified
      encoded address where the length of the address is 0 octets
      following the 16-bit AFI value of 0.

   Anycast Address:  Anycast Address is a term used in this document to
      refer to the same IPv4 or IPv6 address configured and used on
      multiple systems at the same time.  An EID or RLOC can be an
      anycast address in each of their own address spaces.

   Client-side:  Client-side is a term used in this document to indicate
      a connection initiation attempt by an end-system represented by an
      EID.

   Data-Probe:   A Data-Probe is 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 if the destination EID is in the



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      EID-Prefix range configured on the ETR.  Otherwise, the packet is
      discarded.  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.  When using Data-Probes, by sending Map-Requests on
      the underlying routing system, EID-Prefixes must be advertised.

   Egress Tunnel Router (ETR):   An ETR is 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.

   EID-to-RLOC Database:   The EID-to-RLOC Database is 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.  Note that there MAY be transient
      conditions when the EID-Prefix for the site and Locator-Set for
      each EID-Prefix may not be the same on all ETRs.  This has no
      negative implications, since a partial set of Locators can be
      used.

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

   EID-Prefix:   An EID-Prefix is a power-of-two block of EIDs that are
      allocated to a site by an address allocation authority.  EID-
      Prefixes are associated with a set of RLOC addresses.  EID-Prefix
      allocations can be broken up into smaller blocks when an RLOC set
      is to be associated with the larger EID-Prefix block.

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



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   Endpoint ID (EID):   An EID is 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 a destination address
      today, for example, through a Domain Name System (DNS) [RFC1034]
      lookup or Session Initiation Protocol (SIP) [RFC3261] exchange.
      The source EID is obtained via existing mechanisms used to set a
      host's "local" IP address.  An EID used on the public Internet
      MUST have the same properties as any other IP address used in that
      manner; this means, among other things, that it MUST be globally
      unique.  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.  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.  In theory, the bit
      string that represents an EID for one device can represent an RLOC
      for a different device.  When used in discussions with other
      Locator/ID separation proposals, a LISP EID will be called an
      "LEID".  Throughout this document, any references to "EID" refer
      to an LEID.

   Ingress Tunnel Router (ITR):   An ITR is a router that resides in a
      LISP site.  Packets sent by sources inside of the LISP site to
      destinations outside of the site are candidates for encapsulation
      by the ITR.  The ITR treats the 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 routable RLOCs (in
      the RLOC space) 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 host's
      supplied EID).

   LISP Header:   LISP header is a term used in this document to refer
      to the outer IPv4 or IPv6 header, a UDP header, and a LISP-




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      specific 8-octet header that follow the UDP header and that an ITR
      prepends or an ETR strips.

   LISP Router:   A LISP router is a router that performs the functions
      of any or all of the following: ITR, ETR, RTR, Proxy-ITR (PITR),
      or Proxy-ETR (PETR).

   LISP Site:  LISP site is a set of routers in an edge network that are
      under a single technical administration.  LISP routers that reside
      in the edge network are the demarcation points to separate the
      edge network from the core network.

   Locator-Status-Bits (LSBs):  Locator-Status-Bits are present in the
      LISP header.  They are used by ITRs to inform ETRs about the up/
      down status of all ETRs at the local site.  These bits are used as
      a hint to convey up/down router status and not path reachability
      status.  The LSBs can be verified by use of one of the Locator
      reachability algorithms described in Section 10.

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

   Proxy-ETR (PETR):   A PETR is defined and described in [RFC6832].  A
      PETR acts like an ETR but does so on behalf of LISP sites that
      send packets to destinations at non-LISP sites.

   Proxy-ITR (PITR):   A PITR is defined and described in [RFC6832].  A
      PITR acts like an ITR but does so on behalf of non-LISP sites that
      send packets to destinations at LISP sites.

   Recursive Tunneling:   Recursive Tunneling occurs 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.

   Re-Encapsulating Tunneling Router (RTR):   An RTR acts like an ETR to
      remove a LISP header, then acts as an ITR to prepend a new LISP
      header.  This is known as Re-encapsulating Tunneling.  Doing this
      allows a packet to be re-routed by the RTR without adding the
      overhead of additional tunnel headers.  When using multiple



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      mapping database systems, care must be taken to not create re-
      encapsulation loops through misconfiguration.

   Route-Returnability:  Route-returnability is an assumption that the
      underlying routing system will deliver packets to the destination.
      When combined with a nonce that is provided by a sender and
      returned by a receiver, this limits off-path data insertion.  A
      route-returnability check is verified when a message is sent with
      a nonce, another message is returned with the same nonce, and the
      destination of the original message appears as the source of the
      returned message.

   Routing Locator (RLOC):   An RLOC is an IPv4 [RFC0791] or IPv6
      [RFC8200] address of an Egress Tunnel Router (ETR).  An RLOC is
      the output of an EID-to-RLOC mapping lookup.  An EID maps to zero
      or more RLOCs.  Typically, RLOCs are numbered from blocks that are
      assigned to a site at each point to which it attaches to the
      underlay network; where the topology is defined by the
      connectivity of provider networks.  Multiple RLOCs can be assigned
      to the same ETR device or to multiple ETR devices at a site.

   Server-side:  Server-side is a term used in this document to indicate
      that a connection initiation attempt is being accepted for a
      destination EID.

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

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

   xTR:   An 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 and is used synonymously with
      the term "Tunnel Router".  For example, "An xTR can be located at
      the Customer Edge (CE) router" indicates both ITR and ETR
      functionality at the CE router.

4.  Basic Overview

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




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

   Another key LISP concept is the "Tunnel Router".  A Tunnel Router
   prepends LISP headers on host-originated packets and strips 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 ETR strips the new header.  The ITR performs EID-to-
   RLOC lookups to determine the routing path to the ETR, which has the
   RLOC as one of its IP addresses.

   Some basic rules governing LISP are:

   o  End-systems only send to addresses that are EIDs.  EIDs are
      typically IP addresses assigned to hosts (other types of EID are
      supported by LISP, see [RFC8060] for further information).  End-
      systems don't know that addresses are EIDs versus RLOCs but assume
      that packets get to their intended destinations.  In a system
      where LISP is deployed, LISP routers intercept EID-addressed
      packets and assist in delivering them across the network core
      where EIDs cannot be routed.  The procedure a host uses to send IP
      packets does not change.

   o  LISP routers mostly deal with Routing Locator addresses.  See
      details 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 (Classless
      Inter-Domain Routing) 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 Secure SHell (SSH),
      TELNET, or the Simple Network Management Protocol (SNMP)), it MAY
      use an EID that is explicitly assigned for that purpose.  An EID
      that identifies the router as a host MUST NOT be used as an RLOC;
      an EID is only routable within the scope of a site.  A typical BGP
      configuration might demonstrate this "hybrid" EID/RLOC usage where
      a router could use its "host-like" EID to terminate iBGP sessions
      to other routers in a site while at the same time using RLOCs to
      terminate eBGP sessions to routers outside the site.



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   o  Packets with EIDs in them are not expected to be delivered end-to-
      end in the absence of an EID-to-RLOC mapping operation.  They are
      expected to be used locally for intra-site communication or to be
      encapsulated for inter-site communication.

   o  EIDs MAY also be structured (subnetted) in a manner suitable for
      local routing within an Autonomous System (AS).

   An additional LISP header MAY be prepended to packets by a TE-ITR
   when re-routing of the path for a packet is desired.  A potential
   use-case for this would be an ISP router that needs to perform
   Traffic Engineering for packets flowing through its network.  In such
   a situation, termed "Recursive Tunneling", an ISP transit acts as an
   additional ITR, and the RLOC it uses for the new prepended header
   would be either a TE-ETR within the ISP (along an intra-ISP traffic
   engineered path) or a TE-ETR within another ISP (an inter-ISP traffic
   engineered path, where an agreement to build such a path exists).

   In order to avoid excessive packet overhead as well as possible
   encapsulation loops, this document recommends that a maximum of two
   LISP headers can be prepended to a packet.  For initial LISP
   deployments, it is assumed that two headers is sufficient, where the
   first prepended header is used at a site for Location/Identity
   separation and the 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 ETR might be the last-hop router directly
   connected to the destination host.  Another example, perhaps for a
   VPN service outsourced 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.

4.1.  Packet Flow Sequence

   This section provides an example of the unicast packet flow,
   including also Control-Plane information as specified in
   [I-D.ietf-lisp-rfc6833bis].  The example also assumes the following
   conditions:

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





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   o  Each site is multihomed, so each Tunnel Router has an address
      (RLOC) assigned from the service provider address block for each
      provider to which that particular Tunnel Router is attached.

   o  The ITR(s) and ETR(s) are directly connected to the source and
      destination, respectively, but the source and destination can be
      located anywhere in the LISP site.

   o  A Map-Request is sent for an external destination when the
      destination is not found in the forwarding table or matches a
      default route.  Map-Requests are sent to the mapping database
      system by using the LISP Control-Plane protocol documented in
      [I-D.ietf-lisp-rfc6833bis].

   o  Map-Replies are sent on the underlying routing system topology
      using the [I-D.ietf-lisp-rfc6833bis] Control-Plane protocol.

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

   1.  host1.abc.example.com wants to open a TCP connection to
       host2.xyz.example.com.  It does a DNS lookup on
       host2.xyz.example.com.  An A/AAAA record is returned.  This
       address is the destination EID.  The locally assigned address of
       host1.abc.example.com is used as the source EID.  An IPv4 or IPv6
       packet is built and forwarded through the LISP site as a normal
       IP packet until it reaches a LISP ITR.

   2.  The LISP ITR must be able to map the destination EID to an RLOC
       of one of the ETRs at the destination site.  The specific method
       used to do this is not described in this example.  See
       [I-D.ietf-lisp-rfc6833bis] for further information.

   3.  The ITR sends a LISP Map-Request as specified in
       [I-D.ietf-lisp-rfc6833bis].  Map-Requests SHOULD be rate-limited.

   4.  The mapping system helps forwarding the Map-Request to the
       corresponding ETR.  When the Map-Request arrives at one of the
       ETRs at the destination site, it will process the packet as a
       control message.

   5.  The ETR looks at the destination EID of the Map-Request and
       matches it against the prefixes in the ETR's configured EID-to-
       RLOC mapping database.  This is the list of EID-Prefixes the ETR
       is supporting for the site it resides in.  If there is no match,
       the Map-Request is dropped.  Otherwise, a LISP Map-Reply is
       returned to the ITR.




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   6.  The ITR receives the Map-Reply message, parses the message (to
       check for format validity), and stores the mapping information
       from the packet.  This information is stored in the ITR's EID-to-
       RLOC Map-Cache.  Note that the Map-Cache is an on-demand cache.
       An ITR will manage its Map-Cache in such a way that optimizes for
       its resource constraints.

   7.  Subsequent packets from host1.abc.example.com to
       host2.xyz.example.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 that the packet MAY be sent
       to a different ETR than the one that returned the Map-Reply due
       to the source site's hashing policy or the destination site's
       Locator-Set policy.

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

   9.  In order to defer the need for a mapping lookup in the reverse
       direction, an ETR can OPTIONALLY 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 "glean 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 the ITR and the ETR MAY also
       influence the decision the other makes in selecting an RLOC.

5.  LISP Encapsulation Details

   Since additional tunnel headers are prepended, the packet becomes
   larger and 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 Unreachable/Fragmentation-Needed message is
   returned to the source.

   In the case when fragmentation is needed, this specification
   RECOMMENDS that implementations provide support for one of the
   proposed fragmentation and reassembly schemes.  Two existing schemes
   are detailed in Section 7.

   Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the LISP
   architecture supports IPv4 EIDs with IPv6 RLOCs (where the inner
   header is in IPv4 packet format and the outer header is in IPv6
   packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner header



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   is in IPv6 packet format and the outer header is in IPv4 packet
   format).  The next sub-sections illustrate packet formats for the
   homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6), but all 4
   combinations MUST be supported.  Additional types of EIDs are defined
   in [RFC8060].

   As LISP uses UDP encapsulation to carry traffic between xTRs across
   the Internet, implementors should be aware of the provisions of
   [RFC8085], especially those given in section 3.1.11 on congestion
   control for UDP tunneling.

   Implementors are encouraged to consider UDP checksum usage guidelines
   in section 3.4 of [RFC8085] when it is desirable to protect UDP and
   LISP headers against corruption.

5.1.  LISP IPv4-in-IPv4 Header Format



































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

       IHL = IP-Header-Length

5.2.  LISP IPv6-in-IPv6 Header Format

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version|    DSCP   |ECN|           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |         Payload Length        | Next Header=17|   Hop Limit   |
   v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
   O   +                                                               +
   u   |                                                               |
   t   +                     Source Routing Locator                    +
   e   |                                                               |



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   r   +                                                               +
       |                                                               |
   H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   d   |                                                               |
   r   +                                                               +
       |                                                               |
   ^   +                  Destination Routing Locator                  +
   |   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4341        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   L   |N|L|E|V|I|R|K|K|            Nonce/Map-Version                  |
   I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   S / |                 Instance ID/Locator-Status-Bits               |
   P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |Version|    DSCP   |ECN|           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        |  Next Header  |   Hop Limit   |
   v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
   I   +                                                               +
   n   |                                                               |
   n   +                          Source EID                           +
   e   |                                                               |
   r   +                                                               +
       |                                                               |
   H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   d   |                                                               |
   r   +                                                               +
       |                                                               |
   ^   +                        Destination EID                        +
   \   |                                                               |
    \  +                                                               +
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.3.  Tunnel Header Field Descriptions

   Inner Header           (IH):  The inner header is the header on the
      datagram received from the originating host [RFC0791] [RFC8200]
      [RFC2474].  The source and destination IP addresses are EIDs.

   Outer Header: (OH)  The outer header is a new header prepended by an
      ITR.  The address fields contain RLOCs obtained from the ingress



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      router's EID-to-RLOC Cache.  The IP protocol number is "UDP (17)"
      from [RFC0768].  The setting of the Don't Fragment (DF) bit
      'Flags' field is according to rules listed in Sections 7.1 and
      7.2.

   UDP Header:  The UDP header contains an ITR selected source port when
      encapsulating a packet.  See Section 12 for details on the hash
      algorithm used 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:  The 'UDP Checksum' field SHOULD be transmitted as zero
      by an ITR for either IPv4 [RFC0768] and IPv6 encapsulation
      [RFC6935] [RFC6936].  When a packet with a zero UDP checksum is
      received by an ETR, the ETR MUST accept the packet for
      decapsulation.  When an ITR transmits a non-zero value for the UDP
      checksum, it MUST send a correctly computed value in this field.
      When an ETR receives a packet with a non-zero UDP checksum, it MAY
      choose to verify the checksum value.  If it chooses to perform
      such verification, and the verification fails, the packet MUST be
      silently dropped.  If the ETR chooses not to perform the
      verification, or performs the verification successfully, the
      packet MUST be accepted for decapsulation.  The handling of UDP
      zero checksums over IPv6 for all tunneling protocols, including
      LISP, is subject to the applicability statement in [RFC6936].

   UDP Length:  The 'UDP Length' field is set for an IPv4-encapsulated
      packet to be the sum of the inner-header IPv4 Total Length plus
      the UDP and LISP header lengths.  For an IPv6-encapsulated packet,
      the 'UDP Length' field is the sum of the inner-header IPv6 Payload
      Length, the size of the IPv6 header (40 octets), and the size of
      the UDP and LISP headers.

   N: The N-bit is the nonce-present bit.  When this bit is set to 1,
      the low-order 24 bits of the first 32 bits of the LISP header
      contain a Nonce.  See Section 10.1 for details.  Both N- and
      V-bits MUST NOT be set in the same packet.  If they are, a
      decapsulating ETR MUST treat the 'Nonce/Map-Version' field as
      having a Nonce value present.

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








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     x 1 x x 0 x x x
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |N|L|E|V|I|R|K|K|            Nonce/Map-Version                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Locator-Status-Bits                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   E: The E-bit is the echo-nonce-request bit.  This bit MUST be ignored
      and has no meaning when the N-bit is set to 0.  When the N-bit is
      set to 1 and this bit is set to 1, an ITR is requesting that the
      nonce value in the 'Nonce' field be echoed back in LISP-
      encapsulated packets when the ITR is also an ETR.  See
      Section 10.1 for details.

   V: The V-bit is the Map-Version present bit.  When this bit is set to
      1, the N-bit MUST be 0.  Refer to Section 13.1 for more details.
      This bit indicates that the LISP header is encoded in this
      case as:

     0 x 0 1 x x x x
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |N|L|E|V|I|R|K|K|  Source Map-Version   |   Dest Map-Version    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Instance ID/Locator-Status-Bits               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   I: The I-bit is the Instance ID bit.  See Section 8 for more details.
      When this bit is set to 1, the 'Locator-Status-Bits' field is
      reduced to 8 bits and the high-order 24 bits are used as an
      Instance ID.  If the L-bit is set to 0, then the low-order 8 bits
      are transmitted as zero and ignored on receipt.  The format of the
      LISP header would look like this:

     x x x x 1 x x x
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |N|L|E|V|I|R|K|K|            Nonce/Map-Version                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Instance ID                   |     LSBs      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   R: The R-bit is a Reserved bit for future use.  It MUST be set to 0
      on transmit and MUST be ignored on receipt.

   KK:  The KK-bits are a 2-bit field used when encapsulated packets are
      encrypted.  The field is set to 00 when the packet is not
      encrypted.  See [RFC8061] for further information.





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   LISP Nonce:  The LISP 'Nonce' field is a 24-bit value that is
      randomly generated by an ITR when the N-bit is set to 1.  Nonce
      generation algorithms are an implementation matter but are
      required to generate different nonces when sending to different
      RLOCs.  However, the same nonce can be used for a period of time
      when encapsulating to the same ETR.  The nonce is also used when
      the E-bit is set to request the nonce value to be echoed by the
      other side when packets are returned.  When the E-bit is clear but
      the N-bit is set, a remote ITR is either echoing a previously
      requested echo-nonce or providing a random nonce.  See
      Section 10.1 for more details.

   LISP Locator-Status-Bits (LSBs):  When the L-bit is also set, the
      'Locator-Status-Bits' field in the LISP header is set by an ITR to
      indicate to an ETR the up/down status of the Locators in the
      source site.  Each RLOC in a Map-Reply is assigned an ordinal
      value from 0 to n-1 (when there are n RLOCs in a mapping entry).
      The Locator-Status-Bits are numbered from 0 to n-1 from the least
      significant bit of the field.  The field is 32 bits when the I-bit
      is set to 0 and is 8 bits when the I-bit is set to 1.  When a
      Locator-Status-Bit is set to 1, the ITR is indicating to the ETR
      that the RLOC associated with the bit ordinal has up status.  See
      Section 10 for details on how an ITR can determine the status of
      the ETRs at the same site.  When a site has multiple EID-Prefixes
      that result in multiple mappings (where each could have a
      different Locator-Set), the Locator-Status-Bits setting in an
      encapsulated packet MUST reflect the mapping for the EID-Prefix
      that the inner-header source EID address matches.  If the LSB for
      an anycast Locator is set to 1, then there is at least one RLOC
      with that address, and the ETR is considered 'up'.

   When doing ITR/PITR encapsulation:

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

   o  The outer-header 'Differentiated Services Code Point' (DSCP) field
      (or the 'Traffic Class' field, in the case of IPv6) SHOULD be
      copied from the inner-header DSCP field ('Traffic Class' field, in
      the case of IPv6) considering the exception listed below.

   o  The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7
      of the IPv6 'Traffic Class' field) requires special treatment in
      order to avoid discarding indications of congestion [RFC3168].
      ITR encapsulation MUST copy the 2-bit 'ECN' field from the inner
      header to the outer header.  Re-encapsulation MUST copy the 2-bit




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      'ECN' field from the stripped outer header to the new outer
      header.

   When doing ETR/PETR decapsulation:

   o  The inner-header 'Time to Live' field (or 'Hop Limit' field, in
      the case of IPv6) SHOULD be copied from the outer-header 'Time to
      Live' field, when the Time to Live value of the outer header is
      less than the Time to Live value of the inner header.  Failing to
      perform this check can cause the Time to Live of the inner header
      to increment across encapsulation/decapsulation cycles.  This
      check is also performed when doing initial encapsulation, when a
      packet comes to an ITR or PITR destined for a LISP site.

   o  The inner-header 'Differentiated Services Code Point' (DSCP) field
      (or the 'Traffic Class' field, in the case of IPv6) SHOULD be
      copied from the outer-header DSCP field ('Traffic Class' field, in
      the case of IPv6) to the inner-header.

   o  The 'Explicit Congestion Notification' (ECN) field (bits 6 and 7
      of the IPv6 'Traffic Class' field) requires special treatment in
      order to avoid discarding indications of congestion [RFC6040].  If
      the 'ECN' field contains a congestion indication codepoint (the
      value is '11', the Congestion Experienced (CE) codepoint), then
      ETR decapsulation MUST copy the 2-bit 'ECN' field from the
      stripped outer header to the surviving inner header that is used
      to forward the packet beyond the ETR.  These requirements preserve
      CE indications when a packet that uses ECN traverses a LISP tunnel
      and becomes marked with a CE indication due to congestion between
      the tunnel endpoints.  Implementations exist that copy the 'ECN'
      field from the outer header to the inner header even though
      [RFC6040] does not recommend this behavior.  It is RECOMMENDED
      that implementations change to support the behavior in [RFC6040].

   Note that if an ETR/PETR is also an ITR/PITR and chooses to re-
   encapsulate after decapsulating, the net effect of this is that the
   new outer header will carry the same Time to Live as the old outer
   header minus 1.

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

   The Explicit Congestion Notification ('ECN') field occupies bits 6
   and 7 of both the IPv4 'Type of Service' field and the IPv6 'Traffic
   Class' field [RFC6040].  The 'ECN' field requires special treatment



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   in order to avoid discarding indications of congestion [RFC6040].  An
   ITR/PITR encapsulation MUST copy the 2-bit 'ECN' field from the inner
   header to the outer header.  Re-encapsulation MUST copy the 2-bit
   'ECN' field from the stripped outer header to the new outer header.
   If the 'ECN' field contains a congestion indication codepoint (the
   value is '11', the Congestion Experienced (CE) codepoint), then ETR/
   PETR decapsulation MUST copy the 2-bit 'ECN' field from the stripped
   outer header to the surviving inner header that is used to forward
   the packet beyond the ETR.  These requirements preserve CE
   indications when a packet that uses ECN traverses a LISP tunnel and
   becomes marked with a CE indication due to congestion between the
   tunnel endpoints.

6.  LISP EID-to-RLOC Map-Cache

   ITRs and PITRs maintain an on-demand cache, referred as LISP EID-to-
   RLOC Map-Cache, that contains mappings from EID-prefixes to locator
   sets.  The cache is used to encapsulate packets from the EID space to
   the corresponding RLOC network attachment point.

   When an ITR/PITR receives a packet from inside of the LISP site to
   destinations outside of the site a longest-prefix match lookup of the
   EID is done to the Map-Cache.

   When the lookup succeeds, the Locator-Set retrieved from the Map-
   Cache is used to send the packet to the EID's topological location.

   If the lookup fails, the ITR/PITR needs to retrieve the mapping using
   the LISP Control-Plane protocol [I-D.ietf-lisp-rfc6833bis].  The
   mapping is then stored in the local Map-Cache to forward subsequent
   packets addressed to the same EID-prefix.

   The Map-Cache is a local cache of mappings, entries are expired based
   on the associated Time to live.  In addition, entries can be updated
   with more current information, see Section 13 for further information
   on this.  Finally, the Map-Cache also contains reachability
   information about EIDs and RLOCs, and uses LISP reachability
   information mechanisms to determine the reachability of RLOCs, see
   Section 10 for the specific mechanisms.

7.  Dealing with Large Encapsulated Packets

   This section proposes two mechanisms to deal with packets that exceed
   the path MTU between the ITR and ETR.

   It is left to the implementor to decide if the stateless or stateful
   mechanism SHOULD be implemented.  Both or neither can be used, since




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   it is a local decision in the ITR regarding how to deal with MTU
   issues, and sites can interoperate with differing mechanisms.

   Both stateless and stateful mechanisms also apply to Re-encapsulating
   and Recursive Tunneling, so any actions below referring to an ITR
   also apply to a TE-ITR.

7.1.  A Stateless Solution to MTU Handling

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

   1.  Define H to be the size, in octets, of the outer header an ITR
       prepends to a packet.  This includes the UDP and LISP header
       lengths.

   2.  Define L to be the size, in octets, of the maximum-sized packet
       an ITR can send to an ETR without the need for the ITR or any
       intermediate routers to fragment the packet.

   3.  Define an architectural constant S for the maximum size of a
       packet, in octets, an ITR MUST receive from the source so the
       effective MTU can be met.  That is, L = S + H.

   When an ITR receives a packet from a site-facing interface and adds H
   octets worth of encapsulation to yield a packet size greater than L
   octets (meaning the received packet size was greater than S octets
   from the source), it resolves the MTU issue by first splitting the
   original packet into 2 equal-sized fragments.  A LISP header is then
   prepended to each fragment.  The size of the encapsulated fragments
   is then (S/2 + H), which is less than the ITR's estimate of the path
   MTU between the ITR and its correspondent ETR.

   When an ETR receives encapsulated fragments, it treats them as two
   individually encapsulated packets.  It strips the LISP headers and
   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.  Note that reassembly can happen at the ETR if the
   encapsulated packet was fragmented at or after the ITR.

   This behavior MAY be performed by the ITR only when the source host
   originates a packet with the 'DF' field of the IP header 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 send an ICMP Unreachable/
   Fragmentation-Needed message to the source with a value of S, where S
   is (L - H).



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   When the outer-header encapsulation uses an IPv4 header, an
   implementation SHOULD set the DF bit to 1 so ETR fragment reassembly
   can be avoided.  An implementation MAY set the DF bit in such headers
   to 0 if it has good reason to believe there are unresolvable path MTU
   issues between the sending ITR and the receiving ETR.

   This specification RECOMMENDS that L be defined as 1500.

7.2.  A Stateful Solution to MTU Handling

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

   1.  The ITR will keep state of the effective MTU for each Locator per
       Map-Cache entry.  The effective MTU is what the core network can
       deliver along the path between the ITR and ETR.

   2.  When an IPv6-encapsulated packet, or an IPv4-encapsulated packet
       with the DF bit set to 1, exceeds what the core network can
       deliver, one of the intermediate routers on the path will send an
       ICMPv6 "Packet Too Big" message or an ICMPv4 Unreachable/
       Fragmentation-Needed to the ITR, respectively.  The ITR will
       parse the ICMP message to determine which Locator is affected by
       the effective MTU change and then record the new effective MTU
       value in the Map-Cache entry.

   3.  When a packet is received by the ITR from a source inside of the
       site and the size of the packet is greater than the effective MTU
       stored with the Map-Cache entry associated with the destination
       EID the packet is for, the ITR will send an ICMPv4 ICMP
       Unreachable/Fragmentation-Needed or ICMPv6 "Packet Too Big"
       message back to the source.  The packet size advertised by the
       ITR in the ICMP message is the effective MTU minus the LISP
       encapsulation length.

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

8.  Using Virtualization and Segmentation with LISP

   There are several cases where segregation is needed at the EID level.
   For instance, this is the case for deployments containing overlapping
   addresses, traffic isolation policies or multi-tenant virtualization.
   For these and other scenarios where segregation is needed, Instance
   IDs are used.





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   An Instance ID can be carried in a LISP-encapsulated packet.  An ITR
   that prepends a LISP header will copy a 24-bit value used by the LISP
   router to uniquely identify the address space.  The value is copied
   to the 'Instance ID' field of the LISP header, and the I-bit is set
   to 1.

   When an ETR decapsulates a packet, the Instance ID from the LISP
   header is used as a table identifier to locate the forwarding table
   to use for the inner destination EID lookup.

   For example, an 802.1Q VLAN tag or VPN identifier could be used as a
   24-bit Instance ID.  See [I-D.ietf-lisp-vpn] for LISP VPN use-case
   details.

   The Instance ID that is stored in the mapping database when LISP-DDT
   [RFC8111] is used is 32 bits in length.  That means the Control-Plane
   can store more instances than a given Data-Plane can use.  Multiple
   Data-Planes can use the same 32-bit space as long as the low-order 24
   bits don't overlap among xTRs.

9.  Routing Locator Selection

   The Map-Cache contains the state used by ITRs and PITRs to
   encapsulate packets.  When an ITR/PITR receives a packet from inside
   the LISP site to a destination outside of the site a longest-prefix
   match lookup of the EID is done to the Map-Cache (see Section 6).
   The lookup returns a single Locator-Set containing a list of RLOCs
   corresponding to the EID's topological location.  Each RLOC in the
   Locator-Set is associated with a 'Priority' and 'Weight', this
   information is used to select the RLOC to encapsulate.

   The RLOC with the lowest 'Priority' is selected.  An RLOC with
   'Priority' 255 means that MUST NOT be used for forwarding.  When
   multiple RLOC have the same 'Priority' then the 'Weight' states how
   to load balance traffic among them.  The value of the 'Weight'
   represents the relative weight of the total packets that match the
   maping entry.

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

   o  The server-side returns one RLOC.  The client-side can only use
      one RLOC.  The server-side has complete control of the selection.

   o  The server-side returns a list of RLOCs where a subset of the list
      has the same best Priority.  The 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-



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      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  The server-side sets a Weight of zero 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-side determining load
      distribution.  Again, the client can use alternative RLOCs if the
      server-provided list of RLOCs is unreachable.

   o  Either side (more likely 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 that 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.

   Alternatively, RLOC information MAY be gleaned from received tunneled
   packets or EID-to-RLOC Map-Request messages.  A "gleaned" Map-Cache
   entry, one learned from the source RLOC of a received encapsulated
   packet, is only stored and used for a few seconds, pending
   verification.  Verification is performed by sending a Map-Request to
   the source EID (the inner-header IP source address) of the received
   encapsulated packet.  A reply to this "verifying Map-Request" is used
   to fully populate the Map-Cache entry for the "gleaned" EID and is
   stored and used for the time indicated from the 'TTL' field of a
   received Map-Reply.  When a verified Map-Cache entry is stored, data
   gleaning no longer occurs for subsequent packets that have a source
   EID that matches the EID-Prefix of the verified entry.  This
   "gleaning" mechanism is OPTIONAL, refer to Section 16 for security
   issues regarding this mechanism.

   RLOCs that appear in EID-to-RLOC Map-Reply messages are assumed to be
   reachable when the R-bit for the Locator record is set to 1.  When



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   the R-bit is set to 0, an ITR or PITR MUST NOT encapsulate to the
   RLOC.  Neither the information contained in a Map-Reply nor that
   stored in the mapping database system provides reachability
   information for RLOCs.  Note that reachability is not part of the
   mapping system and is determined using one or more of the Routing
   Locator reachability algorithms described in the next section.

10.  Routing Locator Reachability

   Several Data-Plane mechanisms for determining RLOC reachability are
   currently defined.  Please note that additional Control-Plane based
   reachability mechanisms are defined in [I-D.ietf-lisp-rfc6833bis].

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

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

   3.  An ITR/ETR pair can use the 'Echo-Noncing' Locator reachability
       algorithms described in this section.

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

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

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

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

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





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

   When an ETR decapsulates a packet, it will check for any change in
   the 'Locator-Status-Bits' field.  When a bit goes from 1 to 0, the
   ETR, if acting also as an ITR, will refrain from encapsulating
   packets to an RLOC that is indicated as down.  It will only resume
   using that RLOC if the corresponding Locator-Status-Bit returns to a
   value of 1.  Locator-Status-Bits are associated with a Locator-Set
   per EID-Prefix.  Therefore, when a Locator becomes unreachable, the
   Locator-Status-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.  Refer to Section 16 for security related
   issues regarding Locator-Status-Bits.

   When an ETR decapsulates a packet, it knows that it is reachable from
   the encapsulating ITR because that is how the packet arrived.  In
   most cases, the ETR can also reach the ITR but cannot assume this to
   be true, due to the possibility of path asymmetry.  In the presence
   of unidirectional traffic flow from an ITR to an ETR, the ITR SHOULD
   NOT use the lack of return traffic as an indication that the ETR is
   unreachable.  Instead, it MUST use an alternate mechanism to
   determine reachability.

10.1.  Echo Nonce Algorithm

   When data flows bidirectionally between Locators from different
   sites, a Data-Plane mechanism called "nonce echoing" can be used to
   determine reachability between an ITR and ETR.  When an ITR wants to
   solicit a nonce echo, it sets the N- and E-bits and places a 24-bit
   nonce [RFC4086] in the LISP header of the next encapsulated data
   packet.

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

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



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

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

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

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

   The echo-nonce algorithm is bilateral.  That is, if one side sets the
   E-bit and the other side is not enabled for echo-noncing, then the
   echoing of the nonce does not occur and the requesting side may
   erroneously consider the Locator unreachable.  An ITR SHOULD only set
   the E-bit in an encapsulated data packet when it knows the ETR is
   enabled for echo-noncing.  This is conveyed by the E-bit in the RLOC-
   probe Map-Reply message.

11.  EID Reachability within a LISP Site

   A site MAY be multihomed using two or more ETRs.  The hosts and
   infrastructure within a site will be addressed using one or more EID-
   Prefixes that are mapped to the RLOCs of the relevant ETRs in the
   mapping system.  One possible failure mode is for an ETR to lose
   reachability to one or more of the EID-Prefixes within its own site.
   When this occurs when the ETR sends Map-Replies, it can clear the
   R-bit associated with its own Locator.  And when the ETR is also an
   ITR, it can clear its Locator-Status-Bit in the encapsulation data
   header.

   It is recognized that there are no simple solutions to the site
   partitioning problem because it is hard to know which part of the
   EID-Prefix range is partitioned and which Locators can reach any sub-
   ranges of the EID-Prefixes.  Note that this is not a new problem



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   introduced by the LISP architecture.  The problem exists today when a
   multihomed site uses BGP to advertise its reachability upstream.

12.  Routing Locator Hashing

   When an ETR provides an EID-to-RLOC mapping in a Map-Reply message
   that is stored in the Map-Cache of a requesting ITR, the Locator-Set
   for the EID-Prefix MAY contain different Priority and Weight 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 or the traditional
       5-tuple hash can be used.  The traditional 5-tuple hash includes
       the source and destination addresses; source and destination TCP,
       UDP, or Stream Control Transmission Protocol (SCTP) port numbers;
       and the IP protocol number field or IPv6 next-protocol fields of
       a packet that a host originates from within a LISP site.  When a
       packet is not a TCP, UDP, or SCTP packet, the source and
       destination addresses only from the header are used to compute
       the hash.

   2.  Take the hash value and divide it by the number of Locators
       stored in the Locator-Set for the EID-to-RLOC mapping.

   3.  The remainder will yield a value of 0 to "number of Locators
       minus 1".  Use the remainder to select the Locator in the
       Locator-Set.

   Note that when a packet is LISP encapsulated, the source port number
   in the outer UDP header needs to be set.  Selecting a hashed value
   allows core routers that 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 that 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.  The source port
   SHOULD be the same for all packets belonging to the same flow.

   Many core router implementations use a 5-tuple hash to decide how to
   balance packet load across members of a LAG.  The 5-tuple hash
   includes the source and destination addresses of the packet and the
   source and destination ports when the protocol number in the packet




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   is TCP or UDP.  For this reason, UDP encoding is used for LISP
   encapsulation.

13.  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
   which ITRs requested its mappings.  For scalability reasons, it is
   desirable to maintain this approach but need to provide a way for
   ETRs to change their mappings and inform the sites that are currently
   communicating with the ETR site using such mappings.

   This section defines a Data-Plane mechanism for updating EID-to-RLOC
   mappings.  Additionally, the Solicit-Map Request (SMR) Control-Plane
   updating mechanism is specified in [I-D.ietf-lisp-rfc6833bis].

   When adding a new Locator record in lexicographic order to the end of
   a Locator-Set, it is easy to update mappings.  We assume that new
   mappings will maintain the same Locator ordering as the old mapping
   but will 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 Locator-Status-Bits that
   correspond to Locators beyond the list it has cached, it simply
   ignores them.  However, this can only happen for locator addresses
   that are lexicographically greater than the locator addresses in the
   existing Locator-Set.

   When a Locator record is inserted in the middle of a Locator-Set, to
   maintain lexicographic order, SMR procedure
   [I-D.ietf-lisp-rfc6833bis] is used to inform ITRs and PITRs of the
   new Locator-Status-Bit mappings.

   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 Locator-Status-Bit to 0.  So, even if the Locator is in
   the list, it will not be used.  For new mapping requests, the xTRs
   can set the Locator AFI to 0 (indicating an unspecified address), as
   well as setting the corresponding Locator-Status-Bit to 0.  This
   forces ITRs with old or new mappings to avoid using the removed
   Locator.

   If many changes occur to a mapping over a long period of time, one
   will find empty record slots in the middle of the Locator-Set and new
   records appended to the Locator-Set. At some point, it would be




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   useful to compact the Locator-Set so the Locator-Status-Bit settings
   can be efficiently packed.

   We propose here a Data-Plane mechanism (Map-Versioning specified in
   [I-D.ietf-lisp-6834bis]) to update the contents of EID-to-RLOC
   mappings.  Please note that in addition the Solicit-Map Request
   (specified in [I-D.ietf-lisp-rfc6833bis]) is a Control-Plane
   mechanisms that can be used to update EID-to-RLOC mappings.

13.1.  Database Map-Versioning

   When there is unidirectional packet flow between an ITR and ETR, and
   the EID-to-RLOC mappings change on the ETR, it needs to inform the
   ITR so encapsulation to a removed Locator can stop and can instead be
   started to a new Locator in the Locator-Set.

   An ETR, when it sends Map-Reply messages, conveys its own Map-Version
   Number.  This is known as the Destination Map-Version Number.  ITRs
   include the Destination Map-Version Number in packets they
   encapsulate to the site.  When an ETR decapsulates a packet and
   detects that the Destination Map-Version Number is less than the
   current version for its mapping, the SMR procedure described in
   [I-D.ietf-lisp-rfc6833bis] occurs.

   An ITR, when it encapsulates packets to ETRs, can convey its own Map-
   Version Number.  This is known as the Source Map-Version Number.
   When an ETR decapsulates a packet and detects that the Source Map-
   Version Number is greater than the last Map-Version Number sent in a
   Map-Reply from the ITR's site, the ETR will send a Map-Request to one
   of the ETRs for the source site.

   A Map-Version Number is used as a sequence number per EID-Prefix, so
   values that are greater are considered to be more recent.  A value of
   0 for the Source Map-Version Number or the Destination Map-Version
   Number conveys no versioning information, and an ITR does no
   comparison with previously received Map-Version Numbers.

   A Map-Version Number can be included in Map-Register messages as
   well.  This is a good way for the Map-Server to assure that all ETRs
   for a site registering to it will be synchronized according to Map-
   Version Number.

   See [I-D.ietf-lisp-6834bis] for a more detailed analysis and
   description of Database Map-Versioning.







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14.  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,
   determine 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, can use the same group address as the
   destination Routing Locator, use a multicast or unicast Routing
   Locator obtained from a Mapping System lookup, or use other means to
   determine the group address mapping.

   With respect to the source Routing Locator address, the ITR prepends
   its own IP address as the source address of the outer IP header.
   Just like it would if the destination EID was a unicast address.
   This source Routing Locator address, like any other Routing Locator
   address, MUST be globally routable.

   There are two approaches for LISP-Multicast, one that uses native
   multicast routing in the underlay with no support from the Mapping
   System and the other that uses only unicast routing in the underlay
   with support from the Mapping System.  See [RFC6831] and [RFC8378],
   respectively, for details.  Details for LISP-Multicast and
   interworking with non-LISP sites are described in [RFC6831] and
   [RFC6832].

15.  Router Performance Considerations

   LISP is designed to be very "hardware-based forwarding friendly".  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 Forwarding
      Information Base (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



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      logic of testing for particular IP protocol number values is not
      necessary.  There are a few proven cases where no changes to
      existing deployed hardware were needed to support the LISP Data-
      Plane.

   o  On an ITR, prepending a new IP header consists of adding more
      octets to a MAC rewrite string and prepending the string as part
      of the outgoing encapsulation procedure.  Routers that support
      Generic Routing Encapsulation (GRE) tunneling [RFC2784] or 6to4
      tunneling [RFC3056] may already support this action.

   o  A packet's source address or interface the packet was received on
      can be used to select VRF (Virtual Routing/Forwarding).  The VRF's
      routing table can be used to find EID-to-RLOC mappings.

   For performance issues related to Map-Cache management, see
   Section 16.

16.  Security Considerations

   Security considerations for LISP are discussed in [RFC7833].

   A complete LISP threat analysis can be found in [RFC7835], in what
   follows we provide a summary.

   The optional mechanisms of gleaning is offered to directly obtain a
   mapping from the LISP encapsulated packets.  Specifically, an xTR can
   learn the EID-to-RLOC mapping by inspecting the source RLOC and
   source EID of an encapsulated packet, and insert this new mapping
   into its Map-Cache.  An off-path attacker can spoof the source EID
   address to divert the traffic sent to the victim's spoofed EID.  If
   the attacker spoofs the source RLOC, it can mount a DoS attack by
   redirecting traffic to the spoofed victim's RLOC, potentially
   overloading it.

   The LISP Data-Plane defines several mechanisms to monitor RLOC Data-
   Plane reachability, in this context Locator-Status Bits, Nonce-
   Present and Echo-Nonce bits of the LISP encapsulation header can be
   manipulated by an attacker to mount a DoS attack.  An off-path
   attacker able to spoof the RLOC of a victim's xTR can manipulate such
   mechanisms to declare a set of RLOCs unreachable.  This can be used
   also, for instance, to declare only one RLOC reachable with the aim
   of overload it.

   Map-Versioning is a Data-Plane mechanism used to signal a peering xTR
   that a local EID-to-RLOC mapping has been updated, so that the
   peering xTR uses LISP Control-Plane signaling message to retrieve a
   fresh mapping.  This can be used by an attacker to forge the map-



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   versioning field of a LISP encapsulated header and force an excessive
   amount of signaling between xTRs that may overload them.

   Most of the attack vectors can be mitigated with careful deployment
   and configuration, information learned opportunistically (such as LSB
   or gleaning) SHOULD be verified with other reachability mechanisms.
   In addition, systematic rate-limitation and filtering is an effective
   technique to mitigate attacks that aim to overload the Control-Plane.

17.  Network Management Considerations

   Considerations for network management tools exist so the LISP
   protocol suite can be operationally managed.  These mechanisms can be
   found in [RFC7052] and [RFC6835].

18.  Changes since RFC 6830

   For implementation considerations, the following changes have been
   made to this document since RFC 6830 was published:

   o  It is no longer mandated that a maximum number of 2 LISP headers
      be prepended to a packet.  If there is a application need for more
      than 2 LISP headers, an implementation can support more.  However,
      it is RECOMMENDED that a maximum of two LISP headers can be
      prepended to a packet.

   o  The 3 reserved flag bits in the LISP header have been allocated
      for [RFC8061].  The low-order 2 bits of the 3-bit field (now named
      the KK bits) are used as a key identifier.  The 1 remaining bit is
      still documented as reserved.

   o  Data-Plane gleaning for creating map-cache entries has been made
      optional.  If any ITR implementations depend or assume the remote
      ETR is gleaning should not do so.  This does not create any
      interoperability problems since the control-plane map-cache
      population procedures are unilateral and are the typical method
      for map-cache population.

   o  The bulk of the changes to this document which reduces its length
      are due to moving the LISP control-plane messaging and procedures
      to [I-D.ietf-lisp-rfc6833bis].

19.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to this
   Data-Plane LISP specification, in accordance with BCP 26 [RFC8126].




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19.1.  LISP UDP Port Numbers

   The IANA registry has allocated UDP port number 4341 for the LISP
   Data-Plane.  IANA has updated the description for UDP port 4341 as
   follows:

       lisp-data      4341 udp    LISP Data Packets

20.  References

20.1.  Normative References

   [I-D.ietf-lisp-6834bis]
              Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
              Separation Protocol (LISP) Map-Versioning", draft-ietf-
              lisp-6834bis-02 (work in progress), September 2018.

   [I-D.ietf-lisp-rfc6833bis]
              Fuller, V., Farinacci, D., and A. Cabellos-Aparicio,
              "Locator/ID Separation Protocol (LISP) Control-Plane",
              draft-ietf-lisp-rfc6833bis-14 (work in progress),
              September 2018.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <https://www.rfc-editor.org/info/rfc3168>.





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   [RFC6040]  Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", RFC 6040, DOI 10.17487/RFC6040, November
              2010, <https://www.rfc-editor.org/info/rfc6040>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

20.2.  Informative References

   [AFN]      IANA, "Address Family Numbers", August 2016,
              <http://www.iana.org/assignments/address-family-numbers>.

   [CHIAPPA]  Chiappa, J., "Endpoints and Endpoint names: A Proposed",
              1999,
              <http://mercury.lcs.mit.edu/~jnc/tech/endpoints.txt>.

   [I-D.ietf-lisp-introduction]
              Cabellos-Aparicio, A. and D. Saucez, "An Architectural
              Introduction to the Locator/ID Separation Protocol
              (LISP)", draft-ietf-lisp-introduction-13 (work in
              progress), April 2015.

   [I-D.ietf-lisp-vpn]
              Moreno, V. and D. Farinacci, "LISP Virtual Private
              Networks (VPNs)", draft-ietf-lisp-vpn-02 (work in
              progress), May 2018.

   [OPENLISP]
              Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP
              Implementation Report", Work in Progress, July 2008.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.






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   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <https://www.rfc-editor.org/info/rfc1918>.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000,
              <https://www.rfc-editor.org/info/rfc2784>.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
              2001, <https://www.rfc-editor.org/info/rfc3056>.

   [RFC3232]  Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
              by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
              January 2002, <https://www.rfc-editor.org/info/rfc3232>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [RFC4984]  Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report
              from the IAB Workshop on Routing and Addressing",
              RFC 4984, DOI 10.17487/RFC4984, September 2007,
              <https://www.rfc-editor.org/info/rfc4984>.

   [RFC6831]  Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
              Locator/ID Separation Protocol (LISP) for Multicast
              Environments", RFC 6831, DOI 10.17487/RFC6831, January
              2013, <https://www.rfc-editor.org/info/rfc6831>.

   [RFC6832]  Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking between Locator/ID Separation Protocol
              (LISP) and Non-LISP Sites", RFC 6832,
              DOI 10.17487/RFC6832, January 2013,
              <https://www.rfc-editor.org/info/rfc6832>.







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   [RFC6835]  Farinacci, D. and D. Meyer, "The Locator/ID Separation
              Protocol Internet Groper (LIG)", RFC 6835,
              DOI 10.17487/RFC6835, January 2013,
              <https://www.rfc-editor.org/info/rfc6835>.

   [RFC6935]  Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
              UDP Checksums for Tunneled Packets", RFC 6935,
              DOI 10.17487/RFC6935, April 2013,
              <https://www.rfc-editor.org/info/rfc6935>.

   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, DOI 10.17487/RFC6936, April 2013,
              <https://www.rfc-editor.org/info/rfc6936>.

   [RFC7052]  Schudel, G., Jain, A., and V. Moreno, "Locator/ID
              Separation Protocol (LISP) MIB", RFC 7052,
              DOI 10.17487/RFC7052, October 2013,
              <https://www.rfc-editor.org/info/rfc7052>.

   [RFC7215]  Jakab, L., Cabellos-Aparicio, A., Coras, F., Domingo-
              Pascual, J., and D. Lewis, "Locator/Identifier Separation
              Protocol (LISP) Network Element Deployment
              Considerations", RFC 7215, DOI 10.17487/RFC7215, April
              2014, <https://www.rfc-editor.org/info/rfc7215>.

   [RFC7833]  Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A
              RADIUS Attribute, Binding, Profiles, Name Identifier
              Format, and Confirmation Methods for the Security
              Assertion Markup Language (SAML)", RFC 7833,
              DOI 10.17487/RFC7833, May 2016,
              <https://www.rfc-editor.org/info/rfc7833>.

   [RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
              Separation Protocol (LISP) Threat Analysis", RFC 7835,
              DOI 10.17487/RFC7835, April 2016,
              <https://www.rfc-editor.org/info/rfc7835>.

   [RFC8060]  Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
              Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
              February 2017, <https://www.rfc-editor.org/info/rfc8060>.

   [RFC8061]  Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
              (LISP) Data-Plane Confidentiality", RFC 8061,
              DOI 10.17487/RFC8061, February 2017,
              <https://www.rfc-editor.org/info/rfc8061>.





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   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.

   [RFC8111]  Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
              Smirnov, "Locator/ID Separation Protocol Delegated
              Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
              May 2017, <https://www.rfc-editor.org/info/rfc8111>.

   [RFC8378]  Moreno, V. and D. Farinacci, "Signal-Free Locator/ID
              Separation Protocol (LISP) Multicast", RFC 8378,
              DOI 10.17487/RFC8378, May 2018,
              <https://www.rfc-editor.org/info/rfc8378>.






































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Appendix A.  Acknowledgments

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

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

   The authors would like to gratefully acknowledge many people who have
   contributed discussions and ideas to the making of this proposal.
   They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller,
   Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston,
   David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley,
   Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler,
   Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi
   Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Terry
   Manderson, Roger Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van
   Beijnum, Roland Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien
   Saucez, Damian Lezama, Attilla De Groot, Parantap Lahiri, David
   Black, Roque Gagliano, Isidor Kouvelas, Jesper Skriver, Fred Templin,
   Margaret Wasserman, Sam Hartman, Michael Hofling, Pedro Marques, Jari
   Arkko, Gregg Schudel, Srinivas Subramanian, Amit Jain, Xu Xiaohu,
   Dhirendra Trivedi, Yakov Rekhter, John Scudder, John Drake, Dimitri
   Papadimitriou, Ross Callon, Selina Heimlich, Job Snijders, Vina
   Ermagan, Fabio Maino, Victor Moreno, Chris White, Clarence Filsfils,
   Alia Atlas, Florin Coras and Alberto Rodriguez.

   This work originated in the Routing Research Group (RRG) of the IRTF.
   An individual submission was converted into the IETF LISP working
   group document that became this RFC.

   The LISP working group would like to give a special thanks to Jari
   Arkko, the Internet Area AD at the time that the set of LISP
   documents were being prepared for IESG last call, and for his
   meticulous reviews and detailed commentaries on the 7 working group
   last call documents progressing toward standards-track RFCs.

Appendix B.  Document Change Log

   [RFC Editor: Please delete this section on publication as RFC.]







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B.1.  Changes to draft-ietf-lisp-rfc6830bis-18

   o  Posted mid-September 2018.

   o  Changes to reflect comments from Secdir review (Mirja).

B.2.  Changes to draft-ietf-lisp-rfc6830bis-17

   o  Posted September 2018.

   o  Indicate in the "Changes since RFC 6830" section why the document
      has been shortened in length.

   o  Make reference to RFC 8085 about UDP congestion control.

   o  More editorial changes from multiple IESG reviews.

B.3.  Changes to draft-ietf-lisp-rfc6830bis-16

   o  Posted late August 2018.

   o  Distinguish the message type names between ICMP for IPv4 and ICMP
      for IPv6 for handling MTU issues.

B.4.  Changes to draft-ietf-lisp-rfc6830bis-15

   o  Posted August 2018.

   o  Final editorial changes before RFC submission for Proposed
      Standard.

   o  Added section "Changes since RFC 6830" so implementers are
      informed of any changes since the last RFC publication.

B.5.  Changes to draft-ietf-lisp-rfc6830bis-14

   o  Posted July 2018 IETF week.

   o  Put obsolete of RFC 6830 in Intro section in addition to abstract.

B.6.  Changes to draft-ietf-lisp-rfc6830bis-13

   o  Posted March IETF Week 2018.

   o  Clarified that a new nonce is required per RLOC.

   o  Removed 'Clock Sweep' section.  This text must be placed in a new
      OAM document.



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   o  Some references changed from normative to informative

B.7.  Changes to draft-ietf-lisp-rfc6830bis-12

   o  Posted July 2018.

   o  Fixed Luigi editorial comments to ready draft for RFC status.

B.8.  Changes to draft-ietf-lisp-rfc6830bis-11

   o  Posted March 2018.

   o  Removed sections 16, 17 and 18 (Mobility, Deployment and
      Traceroute considerations).  This text must be placed in a new OAM
      document.

B.9.  Changes to draft-ietf-lisp-rfc6830bis-10

   o  Posted March 2018.

   o  Updated section 'Router Locator Selection' stating that the Data-
      Plane MUST follow what's stored in the Map-Cache (priorities and
      weights).

   o  Section 'Routing Locator Reachability': Removed bullet point 2
      (ICMP Network/Host Unreachable),3 (hints from BGP),4 (ICMP Port
      Unreachable),5 (receive a Map-Reply as a response) and RLOC
      probing

   o  Removed 'Solicit-Map Request'.

B.10.  Changes to draft-ietf-lisp-rfc6830bis-09

   o  Posted January 2018.

   o  Add more details in section 5.3 about DSCP processing during
      encapsulation and decapsulation.

   o  Added clarity to definitions in the Definition of Terms section
      from various commenters.

   o  Removed PA and PI definitions from Definition of Terms section.

   o  More editorial changes.

   o  Removed 4342 from IANA section and move to RFC6833 IANA section.





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B.11.  Changes to draft-ietf-lisp-rfc6830bis-08

   o  Posted January 2018.

   o  Remove references to research work for any protocol mechanisms.

   o  Document scanned to make sure it is RFC 2119 compliant.

   o  Made changes to reflect comments from document WG shepherd Luigi
      Iannone.

   o  Ran IDNITs on the document.

B.12.  Changes to draft-ietf-lisp-rfc6830bis-07

   o  Posted November 2017.

   o  Rephrase how Instance-IDs are used and don't refer to [RFC1918]
      addresses.

B.13.  Changes to draft-ietf-lisp-rfc6830bis-06

   o  Posted October 2017.

   o  Put RTR definition before it is used.

   o  Rename references that are now working group drafts.

   o  Remove "EIDs MUST NOT be used as used by a host to refer to other
      hosts.  Note that EID blocks MAY LISP RLOCs".

   o  Indicate what address-family can appear in data packets.

   o  ETRs may, rather than will, be the ones to send Map-Replies.

   o  Recommend, rather than mandate, max encapsulation headers to 2.

   o  Reference VPN draft when introducing Instance-ID.

   o  Indicate that SMRs can be sent when ITR/ETR are in the same node.

   o  Clarify when private addresses can be used.

B.14.  Changes to draft-ietf-lisp-rfc6830bis-05

   o  Posted August 2017.

   o  Make it clear that a Re-encapsulating Tunnel Router is an RTR.



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B.15.  Changes to draft-ietf-lisp-rfc6830bis-04

   o  Posted July 2017.

   o  Changed reference of IPv6 RFC2460 to RFC8200.

   o  Indicate that the applicability statement for UDP zero checksums
      over IPv6 adheres to RFC6936.

B.16.  Changes to draft-ietf-lisp-rfc6830bis-03

   o  Posted May 2017.

   o  Move the control-plane related codepoints in the IANA
      Considerations section to RFC6833bis.

B.17.  Changes to draft-ietf-lisp-rfc6830bis-02

   o  Posted April 2017.

   o  Reflect some editorial comments from Damien Sausez.

B.18.  Changes to draft-ietf-lisp-rfc6830bis-01

   o  Posted March 2017.

   o  Include references to new RFCs published.

   o  Change references from RFC6833 to RFC6833bis.

   o  Clarified LCAF text in the IANA section.

   o  Remove references to "experimental".

B.19.  Changes to draft-ietf-lisp-rfc6830bis-00

   o  Posted December 2016.

   o  Created working group document from draft-farinacci-lisp
      -rfc6830-00 individual submission.  No other changes made.

Authors' Addresses









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

   EMail: farinacci@gmail.com


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

   EMail: vince.fuller@gmail.com


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

   EMail: dmm@1-4-5.net


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

   EMail: darlewis@cisco.com


   Albert Cabellos
   UPC/BarcelonaTech
   Campus Nord, C. Jordi Girona 1-3
   Barcelona, Catalunya
   Spain

   EMail: acabello@ac.upc.edu








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