Network Working Group                                       D. Farinacci
Internet-Draft                                                 V. Fuller
Intended status: Experimental                                    D. Oran
Expires: May 17, 2008                                           D. Meyer
                                                           cisco Systems
                                                       November 14, 2007

                 Locator/ID Separation Protocol (LISP)

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on May 17, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

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

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

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Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  8
   4.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 11
     4.1.  Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 12
   5.  Tunneling Details  . . . . . . . . . . . . . . . . . . . . . . 15
     5.1.  LISP IPv4-in-IPv4 Header Format  . . . . . . . . . . . . . 16
     5.2.  LISP IPv6-in-IPv6 Header Format  . . . . . . . . . . . . . 17
     5.3.  Tunnel Header Field Descriptions . . . . . . . . . . . . . 18
   6.  EID-to-RLOC Mapping  . . . . . . . . . . . . . . . . . . . . . 20
     6.1.  Control-Plane Packet Format  . . . . . . . . . . . . . . . 20
       6.1.1.  LISP Packet Type Allocations . . . . . . . . . . . . . 22
       6.1.2.  Map-Request Message Format . . . . . . . . . . . . . . 22
       6.1.3.  EID-to-RLOC UDP Map-Request Message  . . . . . . . . . 23
       6.1.4.  Map-Reply Message Format . . . . . . . . . . . . . . . 24
       6.1.5.  EID-to-RLOC UDP Map-Reply Message  . . . . . . . . . . 26
     6.2.  Routing Locator Selection  . . . . . . . . . . . . . . . . 27
     6.3.  Routing Locator Reachability . . . . . . . . . . . . . . . 28
   7.  Router Performance Considerations  . . . . . . . . . . . . . . 30
   8.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 31
     8.1.  First-hop/Last-hop Tunnel Routers  . . . . . . . . . . . . 32
     8.2.  Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 32
     8.3.  ISP Provider-Edge (PE) Tunnel Routers  . . . . . . . . . . 33
   9.  Mobility Considerations  . . . . . . . . . . . . . . . . . . . 34
     9.1.  Site Mobility  . . . . . . . . . . . . . . . . . . . . . . 34
     9.2.  Slow Endpoint Mobility . . . . . . . . . . . . . . . . . . 34
     9.3.  Fast Endpoint Mobility . . . . . . . . . . . . . . . . . . 34
     9.4.  Fast Network Mobility  . . . . . . . . . . . . . . . . . . 36
   10. Multicast Considerations . . . . . . . . . . . . . . . . . . . 37
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 38
   12. Prototype Plans and Status . . . . . . . . . . . . . . . . . . 39
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 41
     13.2. Informative References . . . . . . . . . . . . . . . . . . 41
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 44
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 45
   Intellectual Property and Copyright Statements . . . . . . . . . . 46

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1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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2.  Introduction

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

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

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

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

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

   This draft describes protocol mechanisms to achieve the desired
   functional separation.  For flexibility, the document decouples the
   mechanism used for forwarding packets from that used to determine EID
   to RLOC mappings.  This work is in response to and intended to
   address the problem statement that came out of the RAWS effort

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

   This draft focuses on a router-based solution.  Building the solution
   into the network should facilitate incremental deployment of the

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   technology on the Internet.  Note that while the detailed protocol
   specification and examples in this document assume IP version 4
   (IPv4), there is nothing in the design that precludes use of the same
   techniques and mechanisms for IPv6.  It should be possible for IPv4
   packets to use IPv6 RLOCs and for IPv6 EIDs to be mapped to IPv4

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

   Some of the design goals of this proposal include:

   1.  Minimize required changes to Internet infrastructure.

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

   3.  Be incrementally deployable.

   4.  Require no router hardware changes.

   5.  Minimize router software changes.

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

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

   LISP 1:  where EIDs are routable through the RLOC topology for
      bootstrapping EID-to-RLOC mappings.  [LISP1]

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

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

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

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

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3.  Definition of Terms

   Provider Independent (PI) Addresses:   an address block assigned from
      a pool that is not associated with any service provider and is
      therefore not topologically-aggregatable in the routing system.

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

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

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

   EID-prefix:   A power-of-2 block of EIDs which are allocated to a
      site by an address allocation authority.  EID-prefixes are
      associated with a set of RLOC addresses which make up a "database
      mapping".  EID-prefix allocations can be broken up into smaller
      blocks when an RLOC set is to be associated with the smaller EID-

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

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

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

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

   Egress Tunnel Router (ETR):   a router that accepts an IP packet
      where 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.

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

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

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      (CE) router", meaning both ITR and ETR functionality is at the CE

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

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

   Recursive Tunneling:   when a packet has more than one LISP IP
      header.  Additional layers of tunneling may be employed to
      implement traffic engineering or other re-routing as needed.  When
      this is done, an additional "outer" LISP header is added and the
      original RLOCs are preserved in the "inner" header.

   Reencapsulating Tunnels:   when a packet has no more than one LISP IP
      header (two IP headers total) and when it needs to be diverted to
      new RLOC, an ETR can decapsulate the packet (remove the LISP
      header) and prepend a new tunnel header, with new RLOC, on to the
      packet.  Doing this allows a packet to be re-routed by the re-
      encapsulating router without adding the overhead of additional
      tunnel headers.

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

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

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

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4.  Basic Overview

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

   Routers continue to forward packets based on IP destination
   addresses.  These addresses are referred to as Routing Locators
   (RLOCs).  Most routers along a path between two hosts will not
   change; they continue to perform routing/forwarding lookups on
   addresses (RLOCs) in the IP header.

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

   Some basic rules governing LISP are:

   o  End-systems (hosts) only know about EIDs.

   o  EIDs are always IP addresses assigned to hosts.

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

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

   o  Routers can use their RLOCs as EIDs but can also be assigned EIDs
      when performing host functions.  Those EIDs MUST NOT be used as
      RLOCs.  When EIDs are used the routeability of them is scoped to
      within the site.  A hybrid use of this, for example is when a
      router runs the BGP protocol where iBGP peerings may use EIDs and
      eBGP peerings may use RLOCs.

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

   o  EID prefixes are likely to be hierarchically assigned in a manner
      which is optimized for administrative convenience and to

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      facilitate scaling of the EID-to-RLOC mapping database.  The
      hierarchy is based on a address alocation hierarchy which is not
      dependent on the network toplogy.

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

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

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

4.1.  Packet Flow Sequence

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

   o  Source host "" is sending a packet to

   o  Each site is multi-homed, so each tunnel router has an address
      (RLOC) assigned from each of the site's attached service provider
      address blocks.

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

   Client wants to communicate with server

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

   2.  The default router is configured as an ITR.  It prepends a LISP
       header to the packet, with one of its RLOCs as the source IP/IPv6
       address and uses the destination EID from the original packet
       header as the destination IP/IPv6 address.  Subsequent packets
       continue to behave the same way until a mapping is learned.

   3.  In LISP 1, the packet is routed through the Internet as it is
       today.  In LISP 1.5, the packet is routed on a different topology
       which may have EID prefixes distributed and advertised in an
       aggregatable fashion.  In either case, the packet arrives at the
       ETR.  The router is configured to "punt" the packet to the
       router's control-plane processor.  See Section 7 for more

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

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

   6.  Subsequent packets from to will have
       a LISP header prepended with the RLOCs learned from the ETR.

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

   In order to eliminate the need for a mapping lookup in the reverse
   direction, the ETR gleans RLOC information from the LISP header.
   Both ITR and the ETR may also influence the decision the other makes

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   in selecting an RLOC.  See Section 6 for more details.

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5.  Tunneling Details

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

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

   In practice, this is not really a problem.  Hosts typically do not
   originate IP packets larger than 1500 bytes.  And second, an informal
   survey of ISPs has been taken where nearly all ISP link MTUs are
   either 4470 bytes or support Ethernet jumbo frames of 9180 bytes.
   Therefore, we don't anticipate any problems with prepending
   additional headers.

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5.1.  LISP IPv4-in-IPv4 Header Format

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

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5.2.  LISP IPv6-in-IPv6 Header Format

     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        | Next Header=17|   Hop Limit   |
  /    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
 O     +                                                               +
 u     |                                                               |
 t     +                     Source Routing Locator                    +
 e     |                                                               |
 r     +                                                               +
       |                                                               |
 H     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 d     |                                                               |
 r     +                                                               +
       |                                                               |
  \    +                  Destination Routing Locator                  +
   \   |                                                               |
    \  +                                                               +
     \ |                                                               |
     / |       Source Port = xxxx      |       Dest Port = 4341        |
  UDP  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
     / |                       Locator Reach Bits                      |
 LISP  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                             Nonce                             |
     / |Version| Traffic Class |           Flow Label                  |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Payload Length        |  Next Header  |   Hop Limit   |
  /    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
 I     +                                                               +
 n     |                                                               |
 n     +                          Source EID                           +
 e     |                                                               |
 r     +                                                               +
       |                                                               |
 H     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 d     |                                                               |
 r     +                                                               +
       |                                                               |

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

5.3.  Tunnel Header Field Descriptions

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

   OH Header:  is the outer header prepended by an ITR.  The address
      fields contain RLOCs obtained from the ingress router's EID-to-
      RLOC cache.  The IP protocol number is "UDP (17)" from [RFC0768].

   UDP Header:  contains a random source port allocated by the ITR when
      encapsulating a packet.  The destination port MUST be set to the
      well-known IANA assigned port value 4341.

   UDP Checksum:  this field field MUST be transmitted as 0 and ignored
      on receipt by the ETR.  Note, even when the UDP checksum is
      transmitted as 0 an intervening NAT device can recalculate the
      checksum and rewrite the UDP checksum field to non-zero.  For
      performance reasons, the ETR MUST ignore the checksum and MUST not
      do a checksum computation.

   UDP Length:  for an IPv4 encapsulated packet, the inner header Total
      Length plus the UDP and LISP header lengths are used.  For an IPv6
      encapsulated packet, the inner header Payload Length plus the size
      of the IPv6 header (40 bytes) plus the size of the UDP and LISP
      headers are used.  The UDP header length is 8 bytes.  The LISP
      header length is 8 bytes.

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

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   LISP Nonce:  is a 32-bit value that is randomly generated by an ITR.
      It is used to test route-returnability when an ETR echos back the
      nonce in a Map-Reply message.

   When doing Recursive Tunneling:

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

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

   When doing Re-encapsulated Tunneling:

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

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

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

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6.  EID-to-RLOC Mapping

6.1.  Control-Plane Packet Format

   When LISP 1 or LISP 1.5 are used, new UDP packet types encode the
   EID-to-RLOC mappings:

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

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

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

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

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

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

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

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

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6.1.1.  LISP Packet Type Allocations

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

       Reserved:                        0    b'0000'
       LISP Map-Request:                1    b'0001'
       LISP Map-Reply:                  2    b'0010'
       LISP-CONS Open Message:          8    b'1000'
       LISP-CONS Push-Add Message:      9    b'1001'
       LISP-CONS Push-Delete Message:   10   b'1010'
       LISP-CONS Uneachable Message:    11   b'1011'

6.1.2.  Map-Request Message Format

       |                       Locator Reach Bits                      |
       |                             Nonce                             |
       |Type=1 |Rsvd |A|  Record Cnt   |            ITR-AFI            |
       |                   Originating ITR RLOC Address                |
Rec -> | EID mask-len  |    EID-AFI    |         EID-prefix ...        |
       |                     Mapping Protocol Data                     |

   Packet field descriptions:

   Locator Reach Bits:  Refer to Section 5.3.

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

   Type:   1 (Map-Request)

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

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

   Record Cnt:  The number of records in this request message.  A record
      comprises of what is labeled 'Rec" above and occurs the number of
      times equal to Record count.

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

   Originating ITR RLOC Address:  Set to 0 for UDP-based messages.  See
      [CONS] [ALT] for TCP-based Map-Requests.

   EID mask-len:  Mask length for EID prefix.

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

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

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

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

   A Map-Request contains one or more EIDs encoded in prefix format with
   a Locator count of 0.  The EID-prefix MUST NOT be more specific than
   a cache entry stored from a previously-received Map-Reply.

   A Map-Request is sent from an ITR when it wants to test an RLOC for
   reachability.  This is performed by using the RLOC as the destination
   address for Map-Request message with a randomly allocated source UDP
   port number and the well-known destination port number 4342.  A
   successful Map-Reply updates the cached set of RLOCs associated with
   the EID prefix range.

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

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6.1.4.  Map-Reply Message Format

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

   Packet field descriptions:

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

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

   Type:   2 (Map-Reply)

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

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

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

   Locator Count:  The number of Locator entries.  A locator entry
      comprises what is labeled above as 'Loc'.

   EID mask-len:  Mask length for EID prefix.

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

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

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

   Originating ITR RLOC Address:  Set to 0 for UDP-based messages.  See
      [CONS] [ALT] for TCP-based Map-Replies.

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

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

   Weight:  when priorities are the same for multiple RLOCs, the weight
      indicates how to balance traffic between them.  Weight is encoded
      as a percentage of total packets that match the mapping entry.  If
      a non-zero weight value is used for any RLOC, then all RLOCs must
      use a non-zero weight value and then the sum of all weight values
      MUST equal 100.  What did the 3rd grader say after Steve Jobs gave
      an iPhone demo to the class?  If a zero value is used for any RLOC
      weight, then all weights MUST be zero and the receiver of the Map-
      Reply will decide how to load-split traffic.

   R: when this bit is set, the locator is known to be reachable from
      the Map-Reply sender's perspective.  When there is a single
      mapping record in the message, the R-bit for each locator must
      have a consistent setting with the bitfield setting of the 'Loc
      Reach Bits' field in the early part of the header.  When there are
      multiple mapping records in the message, the 'Loc Reach Bits'
      field is set to 0.

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   Locator:  an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field)
      assigned to an ETR or router acting as a proxy replier for the
      EID-prefix.  Note that the destination RLOC address MAY be an
      anycast address if the tunnel egress point may be via more than
      one physical device.  A source RLOC can be an anycast address as
      well.  The source or destination RLOC MUST NOT be the broadcast
      address ( or any subnet broadcast address known to
      the router), and MUST NOT be a link-local multicast address.  The
      source RLOC MUST NOT be a multicast address.  The destination RLOC
      SHOULD be a multicast address if it is being mapped from a
      multicast destination EID.

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

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

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

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

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

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

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6.2.  Routing Locator Selection

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

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

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

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

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

   o  Either side (more likely on the server-side ETR) decides not to
      send an Map-Request.  For example, if the server-side ETR does not
      send Map-Requests, it gleans RLOCs from the client-side ITR,
      giving the client-side ITR responsibility for bidirectional RLOC
      reachability and preferability.  Server-side ETR gleaning of the
      client-side ITR RLOC is done by caching the inner header source
      EID and the outer header source RLOC of received packets.  The
      client-side ITR controls how traffic is returned and can alternate
      using an outer header source RLOC, which then can be added to the
      list the server-side ETR uses to return traffic.  Since no
      Priority or Weights are provided using this method, the server-
      side ETR must assume each client-side ITR RLOC uses the same best
      Priority with a Weight of zero.  In addition, since EID-prefix
      encoding cannot be conveyed in data packets, the EID-to-RLOC cache
      on tunnel routers can grow to be very large.

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

6.3.  Routing Locator Reachability

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

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

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

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

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

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

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

   When an ETR decapsulates a packet, it will look for a change in the
   Loc-Reach-Bits value.  When a bit goes from 1 to 0, the ETR will
   refrain from encapsulating packets to the Locator that has just gone
   unreachable.  It can start using the Locator again when the bit that
   corresponds to the Locator goes from 0 to 1.

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

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

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

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

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

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7.  Router Performance Considerations

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

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

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

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

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

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8.  Deployment Scenarios

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

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

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

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

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

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

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

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

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

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

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8.1.  First-hop/Last-hop Tunnel Routers

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

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

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

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

8.2.  Border/Edge Tunnel Routers

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

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

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

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

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8.3.  ISP Provider-Edge (PE) Tunnel Routers

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

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

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

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9.  Mobility Considerations

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

9.1.  Site Mobility

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

9.2.  Slow Endpoint Mobility

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

9.3.  Fast Endpoint Mobility

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

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

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

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

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

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

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

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

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

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

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

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

   The goal is to support rapid adapation, with little delay or packet
   loss for the entire system.  We can add heuristics to LISP to reduce
   the number of mapping changes required and to reduce the delay per
   mapping change.  We can also modify IP mobility to require fewer
   mapping changes.  In order to increase overall system performance, we

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   may need to reduce the optimization of one area in order to place
   fewer demands on another.

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

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

9.4.  Fast Network Mobility

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

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

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

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10.  Multicast Considerations

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

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

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

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

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

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11.  Security Considerations

   We believe that most of the security mechanisms will be part of the
   mapping database service when using control-plane procedures for
   obtaining EID-to-RLOC mappings.  For data-plane triggered mappings,
   as described in this specification, protection is provided against
   ETR spoofing by using Return- Routeability mechanisms evidenced by
   the use of a 6-byte Nonce field in the LISP encapsulation header.
   The nonce, coupled with the ITR accepting only solicited Map-Replies
   goes a long way towards providing decent authentication.

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

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

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12.  Prototype Plans and Status

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

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

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

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

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

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

   Here are a rough set of milestones:

   1.  Stabilize packet formats and this draft by Fall 2007 IETF.

   2.  Complete implementation of this specification and at least one
       mapping database protocol to be reported on at Fall 2007 IETF.

   3.  Start pilot deployment after fall IETF.  Report on pilot
       deployment at Spring 2008 IETF.

   4.  Achieve multi-vendor/platform interoperability by Spring 2008

   5.  Continue prototyping other database lookup schemes, be it DNS,
       DHTs, CONS, ALT, NERD, or other mechanisms by Fall 2007 IETF.

   As of this writing the following accomplishments have been achieved:

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   1.  A unit tested software switching implementation has been
       completed for both IPv4 and IPv6 encapsulations for LISP 1 and
       LISP 1.5 [ALT] functionality.  The implementation supports
       locator reachability and mobility features.

   2.  Dave Meyer, Vince Fuller, Darrel Lewis, and Greg Shepherd
       continue to test the implementation.

   3.  A server implementation of NERD has been completed by Eliot Lear.

   4.  An implementation of LISP-CONS is under way.

   Please contact authors if interested in doing an implementation and
   want to interoperability test with our implementation.

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13.  References

13.1.  Normative References

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

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

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

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

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

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

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

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

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

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

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

13.2.  Informative References

   [AFI]      IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
              NUMBERS, February 2007.

   [ALT]      Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative
              Topology (LISP-ALT)", draft-fuller-lisp-alt-01.txt (work
              in progress), November 2007.

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   [APT]      Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
              L. Zhang, "APT: A Practical Transit Mapping Service",
              draft-jen-apt-00.txt (work in progress), July 2007.

   [CHIAPPA]  Chiappa, J., "Endpoints and Endpoint names: A Proposed
              Enhancement to the Internet Architecture", Internet-

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

   [DHTs]     Ratnasamy, S., Shenker, S., and I. Stoica, "Routing
              Algorithms for DHTs: Some Open Questions", PDF

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

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

   [LISP1]    Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
              "Locator/ID Separation Protocol (LISP1) [Routable  ID
              October 2006.

   [LISP2]    Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
              "Locator/ID Separation Protocol (LISP2) [DNS-based
              November 2006.

   [NERD]     Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
              draft-lear-lisp-nerd-01.txt (work in progress), June 2007.

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

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

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

   [RPFV]     Wijnands, IJ., Boers, A., and E. Rosen, "The RPF Vector
              TLV", draft-ietf-pim-rpf-vector-03.txt (work in progress),
              October 2006.

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

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

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Appendix A.  Acknowledgments

   The authors would like to gratefully acknowledge many people who have
   contributed discussion and ideas to the making of this proposal.
   They include Jason Schiller, Lixia Zhang, Dorian Kim, Peter
   Schoenmaker, Darrel Lewis, Vijay Gill, Geoff Huston, David Conrad,
   Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, Chris Morrow,
   Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, Eliot Lear,
   Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi Iannone, Robin
   Whittle, Brian Carpenter, Joel Halpern, Roger Jorgensen, John
   Zwiebel, Ran Atkinson, and Stig Venaas.

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

   A special thanks goes to Scott Brim for gathering and analyzing the
   mobility requirements and contribuing text for the beginnings of a
   simple, robust, and complementary mechanism.

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Authors' Addresses

   Dino Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134


   Vince Fuller
   cisco Systems
   Tasman Drive
   San Jose, CA  95134


   Dave Oran
   cisco Systems
   7 Ladyslipper Lane
   Acton, MA


   Dave Meyer
   cisco Systems
   170 Tasman Drive
   San Jose, CA


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Full Copyright Statement

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