Network Working Group                                       D. Farinacci
Internet-Draft                                                 V. Fuller
Intended status: Experimental                                    D. Oran
Expires: July 21, 2007                                     cisco Systems
                                                        January 17, 2007

                 Locator/ID Separation Protocol (LISP)

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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Copyright Notice

   Copyright (C) The Internet Society (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.

Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  6
   4.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 10
   5.  Tunneling Details  . . . . . . . . . . . . . . . . . . . . . . 12
   6.  EID-to-RLOC Mapping  . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Control-Plane Packet Format  . . . . . . . . . . . . . . . 14
       6.1.1.  EID-to-RLOC Mapping Request Message  . . . . . . . . . 16
       6.1.2.  EID-to-RLOC Mapping Reply Message  . . . . . . . . . . 16
     6.2.  Routing Locator Selection and Reachability . . . . . . . . 16
   7.  Router Performance Considerations  . . . . . . . . . . . . . . 19
   8.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  First-hop/Last-hop Tunnel Routers  . . . . . . . . . . . . 21
     8.2.  Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 21
     8.3.  ISP Provider-Edge (PE) Tunnel Routers  . . . . . . . . . . 21
   9.  Multicast Considerations . . . . . . . . . . . . . . . . . . . 23
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   11. Prototype Plans  . . . . . . . . . . . . . . . . . . . . . . . 25
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     12.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
   Intellectual Property and Copyright Statements . . . . . . . . . . 30

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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.  Mobility with session survivability.  Because session state is
       associated with a persistent host EID, it should be possible for
       a host (or a collection of hosts) to move to a different point in
       the network topology (whether by changing providers or by
       physically moving) without disruption of connectivity.

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

   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

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

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   Related work on host-based solutions may be found described as GSE
   [GSE], Shim6 [SHIM6], and HIP [RFC4423].  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.

   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 IP 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.

   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 address today, typically through a DNS lookup.  The
      source EID is obtained via existing mechanisms used to set a hosts
      "local" IP address.  LISP uses PI blocks for EIDs; such EIDs MUST
      NOT be used as a 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.

   End-system:   is an IP device that originates packets with a single
      IP 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

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      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).

   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.

   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 to RLOC mappings.  Each potential ETR
      typically contains a small piece of the database: the EID-to-RLOC
      mappings for the EIDs "behind" the router.  These map to one of
      the router's own, globally-visible, IP addresses.  This block of
      EIDs which map to a particular RLOC is described as an "EID
      prefix".  Pieces of the database may also be aggregated and may be
      contained in other routers that "proxy" reply for ETRs.

   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.

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   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 IP
      header an ITR prepends or an ETR strips.

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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

   o  EIDs are not expected to be usable for end-to-end communication in
      the absence of an EID-to-RLOC mapping operation.

   o  EID prefixes are likely to be hierarchically assigned in a manner
      which is optimized for administrative convenience and to
      facilitate scaling of the EID-to-RLOC mapping database.

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

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   An additional LISP header may be pre-pended to packets by a transit
   router 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 ETR within the
   ISP (along intra-ISP traffic engineered path) or in an 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 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

   1. wants to open a TCP connection to
       It does a DNS lookup on  An A 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 packet is built using the EIDs in the IP 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 it's RLOCs as the source IP

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       address and uses the destination EID from the original packet
       header as the destination IP address.

   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 ICMP EID-to-RLOC Mapping
       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 ICMP
       message is one of the ETR's RLOCs (one of the RLOCs that is
       embedded in the ICMP payload).

   5.  The ITR receives the ICMP 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
   in selecting an RLOC.  See section Section 6 for more details.

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5.  Tunneling Details

   This section describes the tunnel header details.  LISP uses the
   existing, IP-in-IP encapsulation as described below.

   LISP IP-in-IP 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 = 4 |         Header Checksum       |
  \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \   |                    Source Routing Locator                     |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                 Destination Routing Locator                   |
     / |Version|  IHL  |Type of Service|          Total Length         |
    /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /   |         Identification        |Flags|      Fragment Offset    |
  /    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IH     |  Time to Live |    Protocol   |         Header Checksum       |
  \    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \   |                           Source EID                          |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                         Destination EID                       |

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

   Header OH 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 "IP in IP encapsulation" from

   When doing Recursive Tunneling:

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

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

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   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.

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6.  EID-to-RLOC Mapping

6.1.  Control-Plane Packet Format

   When LISP 1 or LISP 1.5 are used, a new ICMP packet type encodes 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 = 1 |         Header Checksum       |
       |                    Source Routing Locator                     |
       |                 Destination Routing Locator                   |

       |  Type = 42    |     Code      |          Checksum             |
       |  Record Count |                 Unused                        |
       |  RLOC Count   | EID Mask Len  |      EID Prefix 1 ...         |
       |   Priority    |   Weight      |    Routing Locator 1 ...      |
       |                          .  .  .                              |
       |   Priority    |   Weight      |    Routing Locator n ...      |
       |                            .  .  .                            |
       |                                                               |
       | Locator Count | EID Mask Len  |      EID Prefix n ...         |
       |   Priority    |   Weight      |    Routing Locator 1 ...      |
       |                          .  .  .                              |
       |   Priority    |   Weight      |    Routing Locator n ...      |

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   Packet field descriptions:

   ICMP Type -   set to 42 for an "EID-to-RLOC Mapping" message.

   ICMP Code -   1 is a Request, 2 is a Reply.

   ICMP Checksum -   1's complement checksum of the entire ICMP packet.

   Unused -   transmitted as 0 and ignored on receipt.

   Record Count -   unassigned number of records contained in the
      message.  A record contains a mapping of an EID-prefix to a set of
      RLOCs.  A record count of 0 is illegal.

   RLOC Count -   The number of RLOCs associated with this EID prefix.

   EID Mask Len -   The mask length of the EID prefix.  By encoding an
      EID prefix, a set of RLOCs can be associated with a block of EIDs.
      Values are between 0 and 32 inclusive.

   EID Prefix -   the encoded EID, represented as an IP address.  This
      field is 4 bytes in length.

   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
      should 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.  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.  Going to buy an
      iPhone?  If a zero value is used for any RLOC weight, then all
      weights must be zero and the receiver of the Reply will decide how
      to load-split traffic.

   Routing Locator (RLOC) -   an IP address assigned to an ETR or router
      acting as a proxy replier for the EID-prefix.  Note that the RLOC
      address can be an anycast address if the tunnel egress point may
      be via more than one physical device.  The source or destination
      RLOC MUST NEVER be the broadcast address (  The
      source RLOC MUST NEVER be a multicast address.  The destination
      RLOC SHOULD be a multicast address if it is being mapped from a
      multicast destination EID.

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6.1.1.  EID-to-RLOC Mapping Request Message

   A Request contains one or more EIDs encoded in prefix format with a
   Locator count of 0.  The EID-prefix should be no more specific than a
   cache entry stored from a previously-received Reply.

   A request is sent from an ITR when it wants to test an RLOC for
   reachability.  This testing is performed by using the RLOC as the
   destination address for type of ICMP packet.  A successful reply
   updates the cached set of RLOCs associated with the EID prefix range.

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

6.1.2.  EID-to-RLOC Mapping Reply Message

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

   Note that a Reply may contain different EID-prefix granularity
   (prefix + length) than the Request which triggers it.  This might
   occur if a Request were for a prefix that had been returned by an
   earlier 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 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 blocks of EIDs into EID-prefixes will
   allow one Reply to suppress further Requests for multiple EIDs in the
   EID-prefix range.

6.2.  Routing Locator Selection and Reachability

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

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   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) decides not send an
      ICMP EID-to-RLOC Mapping Request.  For example, if the server-side
      does not send Requests, it gleans RLOCs from the client-side,
      giving the client-side responsibility for bidirectional RLOC
      reachability and preferability.  Server-side gleaning of the
      client-side RLOC is done by caching the inner header source EID
      and the outer header source RLOC of received packets.  The client-
      side 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 uses to return traffic.  Since no Priority or Weights
      are provided using this method, the server-side must assume each
      client-side 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.

   An RLOC in the list returned by a EID-to-RLOC Mapping Reply is only
   known to be reachable when an EID-to-RLOC Mapping Request sent using
   it as the destination IP address results in the a successful reply
   containing it as a source IP address.  Obviously, sending such probes
   increases the number of control messages originated by tunnel routers

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   for active flows, so RLOC as assumed to be reachable when they are

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

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

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7.  Router Performance Considerations

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

   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 or 6to4 tunneling 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 is was received) can be associated with a
      VRF, 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 ingress 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 tunneling.

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

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

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

   o  In general, using more ITRs doesn't increase management load,
      since caches are built and stored dynamically.  On the other hand,
      more ETRs does require more management since EID-prefix-to-Locator
      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-Locator 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
   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 be also deployed in edge switches.  These
   devices generally have layer-2 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.

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

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   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.  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 (the destination EID) 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.  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.

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10.  Security Considerations

   ICMP EID-to-RLOC Reply messages are authoritative to the same extent
   DNS Replies are.  LISP is no less secure than DNS and at this time we
   do not intend to add any additional security mechanisms to the

   However, in future versions of this draft, we will add cryptographic
   authenticity to ICMP EID-to-RLOC messages.

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11.  Prototype Plans

   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, ICMP-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 this draft by Spring 2007 Prague IETF.

   2.  Start implementation to report on by Spring 2007 Prague IETF.

   3.  Start pilot deployment between spring and summer IETFs.  Report
       on deployment at Summer 2007 Chicago IETF.

   4.  Achieve multi-vendor interoperability by Summer 2007 Chicago

   5.  Consider prototyping other database lookup schemes, be it DNS,
       DHTs, or other mechanisms by Fall 2007 IETF.

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12.  References

12.1.  Normative References

   [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.

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              October 1996.

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

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

12.2.  Informative References

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

   [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.

   [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.

   [RAWS]     Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
              Workshop on Routing and  Addressing",
              draft-iab-raws-report-00.txt (work in progress),

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              November 2006.

   [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 Dave Meyer, Jason Schiller, Lixia Zhang, Dorian Kim,
   Peter Schoenmaker, Darrel Lewis, Vijay Gill, Geoff Huston, David
   Conrad, Ron Bonica, Ted Seely, Mark Townsley, Chris Morrow, Brian
   Weis, and Dave McGrew.

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

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Authors' Addresses

   Dino Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134


   Vince Fuller
   cisco Systems
   Tasman Drive
   San Jose, CA  95134


   Dave Oran
   cisco Systems
   7 Ladyslipper Lane
   Acton, MA


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Full Copyright Statement

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