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Network Working Group                                            S. Brim
Internet-Draft                                                N. Chiappa
Intended status: Experimental                               D. Farinacci
Expires: May 17, 2008                                          V. Fuller
                                                                D. Lewis
                                                                D. Meyer
                                                       November 14, 2007

   LISP-CONS: A Content distribution Overlay Network Service for LISP

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   The Content distribution Overlay Network Service for LISP (LISP-CONS)
   is a protocol for distributing identifier-to-locator mappings for the
   Locator/ID Separation Protocol (LISP).  LISP-CONS is not a routing
   protocol.  LISP-CONS is designed to scale by using a hierarchical
   content distribution system comprised of Tunnel Routers, Content

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   Access Resources, and Content Distribution Resources.

Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  LISP-CONS Name Spaces  . . . . . . . . . . . . . . . . . .  5
     3.2.  LISP-CONS Network Elements . . . . . . . . . . . . . . . .  5
     3.3.  Relationship Between LISP-CONS Network Elements  . . . . .  7
   4.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .  7
   5.  The LISP-CONS Protocol . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Building the LISP-CONS Database  . . . . . . . . . . . . . 10
     5.2.  Querying the LISP-CONS Database  . . . . . . . . . . . . . 11
     5.3.  Maintaining the LISP-CONS Database . . . . . . . . . . . . 13
       5.3.1.  An EID-Prefix Is Administratively Removed From The
               Infrastructure . . . . . . . . . . . . . . . . . . . . 13
       5.3.2.  A CAR's Connectivity Changes . . . . . . . . . . . . . 14
       5.3.3.  A CAR Becomes Unreachable  . . . . . . . . . . . . . . 15
       5.3.4.  A CDR Becomes Unreachable  . . . . . . . . . . . . . . 15
   6.  LISP-CONS Message Types  . . . . . . . . . . . . . . . . . . . 16
   7.  Operational Considerations . . . . . . . . . . . . . . . . . . 17
   8.  LISP-CONS and Locator Reachability . . . . . . . . . . . . . . 17
   9.  LISP-CONS and Mobility . . . . . . . . . . . . . . . . . . . . 17
   10. Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 17
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 18
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
     12.1. Apparent LISP-CONS Vunerabilities  . . . . . . . . . . . . 19
     12.2. Survey of LISP-CONS Security Mechanisms  . . . . . . . . . 19
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 20
     14.2. Informative References . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
   Intellectual Property and Copyright Statements . . . . . . . . . . 23

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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].

2.  Introduction

   The Content distribution Overlay Network Service for LISP, or LISP-
   CONS, is a control-plane protocol for distributing identifier-to-
   locator mappings for the Locator/ID Separation Protocol (LISP)
   [LISP].  The properties of such a "locator/id split" have been
   discussed in depth in various venues dating back to [CHIAPPA] and
   [RFC1498], and as such will not be reviewed here.  Rather, the reader
   is referred to the above references for an outline of the various
   benefits that may be realized by separating the functionality of IP
   addresses into separate Endpoint Identifier and Routing Locator name

   LISP-CONS operates on a distributed Endpoint Identifier-to-Routing
   Locator (EID-to-RLOC) database.  This database is distributed among
   the authoritative Answering Content Access Resources (Answering-CAR).
   An Answering-CAR (aCAR) advertises "reachability" for its EID-to-RLOC
   mappings through a hierarchical network of Content Distribution
   Resources (CDRs) (but importantly, not the mapping itself), and
   responds to mapping requests from the system.  A CAR may also request
   mappings from the system (this a Querying-CAR, or qCAR).  Ingress
   Tunnel Routers (ITRs) connect to one or more qCARs to query the
   system for EID-to-RLOC bindings; the qCAR then queries the system on
   behalf of the ITR.  These queries follow the overlay network to the
   authoritative aCAR, which responds with the mapping.  This response
   may then be cached by the 'local' CAR.  Finally, note that neither a
   qCAR or aCAR need to hold the entire EID-to-RLOC database.  Rather,
   the EID-to-RLOC translations are explicitly pulled by the ITRs by
   querying one or more of its connected qCARs.

   Note that LISP-CONS is not designed for the "fast-mobility" case.
   That is, it is envisioned that the mappings distributed by LISP-CONS
   are reasonably static.  LISP-CONS is also not designed to carry
   Locator Reachability status information; see [LISP] for details on
   how LISP determines locator reachability.

   LISP-CONS seeks to control the "state * rate" scaling properties of
   the mapping service by first observing that the host mapping state is
   likely to be quite large (some estimates put the size of this
   database to be on the order of 10^10 hosts).  As a result, even with
   aggressive aggregation, the "rate" of change of the mapping database

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   must be kept small.  LISP-CONS manages the rate problem by
   distributing highly aggregated information about the location of the
   EID-to-RLOC mappings (which are assumed to change at low frequency)
   over a peering network.  The peering network is comprised of ITRs,
   CARs and CDRs.

   In summary, LISP-CONS is a hybrid "push/pull" protocol in which
   information about the existence of a particular mapping is "pushed"
   at the higher levels of the aggregation hierarchy, while the actual
   EID-to-RLOC mappings are "pulled" from the network elements at the
   lowest level of the hierarchy.  In particular, LISP-CONS carries
   mapping requests and replies to and from the lowest level of the
   hierarchy where the EID-to-RLOC mappings reside.

   While this draft focuses on a router-based solution, there is no
   architectural reason that LISP-CONS functionality could not be
   implemented in other devices (i.e., hosts).  However, in keeping with
   the architectural direction taken by the LISP data-plane proposal
   [LISP], LISP-CONS is based on the the theory that building the
   solution into the network should facilitate incremental deployment of
   the technology on the Internet.  In order to minimize the required
   investment in deployment of new hardware, it is assumed that much, if
   not all, the initial implementation will be in routers.  Finally,
   while the detailed protocol specification and examples in this
   document assume IP version 4 (IPv4), there is nothing in the design
   that precludes the use of the same techniques and mechanisms for

   The remainder of this document is organized as follows: Section 3
   provides the set of definitions that are used in this document, and
   Section 4 provides an overview of LISP-CONS operation.  Section 5
   describes the LISP-CONS protocol, and Section 6 provides details of
   the LISP-CONS message types.  Section 7 outlines operational
   considerations, Section 8 discusses locator reachability, and
   Section 9 considers the interaction of LISP-CONS with mobile nodes.
   Section 12 outlines security considerations for LISP-CONS.

   Finally, this proposal (as well as the LISP data-plane proposal) was
   stimulated by the problem statement effort at the IAB Routing and
   Addressing Workshop (RAWS) [I-D.iab-raws-report], which took place in
   Amsterdam in October 2006.

3.  Definition of Terms

   The LISP-CONS protocol operates on two name spaces and is comprised
   of four network elements.  This section provides high-level
   definitions of the LISP-CONS name spaces, network elements, and

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   message types.

3.1.  LISP-CONS Name Spaces

    Endpoint ID (EID):  A 32- or 128-bit value used in the source and
      destination fields of the first (most inner) LISP header of a
      packet.  A packet that is emitted by a system contains EIDs in its
      headers and and LISP headers are prepended only when the packet
      hits an Ingress Tunnel Router (ITR) on the data path to the
      destination EID.

      In LISP-CONS, EID-prefixes MUST BE assigned in a hierarchical
      manner (in power-of-two or larger chunks) such that they can be
      aggregated either by Content Access Resources or Content
      Distribution Resources (see below).  In addition, a site may have
      site-local structure in how EIDs are topologically organized
      (subnetting) for routing within the site; this structure is not
      visible to the global routing system.

   EID-Prefix Aggregate:  A set of EID-prefixes said to be aggregatable
      in the [RFC4632] sense.  That is, an EID-Prefix aggregate is
      defined to be a single contiguous power-of-two EID-prefix block.
      Such a block is characterized by a prefix and a mask.

   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 Provider Aggregatable (PA) addresses.

    EID-to-RLOC Mapping:  A binding between and EID and the RLOC-set
      that can be used to reach the EID.  We use the term "mapping" in
      this document to refer to a EID-to-RLOC mapping.

3.2.  LISP-CONS Network Elements

   LISP-CONS consists of the four network element types described below.
   Peering connections between these element types use RLOCs so that the
   underlying routing system can keep the LISP-CONS peering connections
   up (i.e., to avoid circular dependencies on the mapping system).
   Each peering connection is required to be configured with a keyed-
   hash message authentication code (HMAC) key.  A connection MUST NOT
   be established without the TCP HMAC option included.

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   Content Distribution Resource (CDR):  A CDR provides aggregation of
      EID prefix lists, propagation of EID-prefix lists to parent CDRs,
      and routing of mapping requests to and from CARs.

      There may be several levels of aggregation of CDRs.  CDRs do not
      themselves carry EID prefix to RLOC mappings.  CDRs are arranged
      in a hierarchical manner in order to enable aggressive aggregation
      of EID-prefixes.

   Content Access Resource (CAR):  A CAR fills one or both of the
      following roles:

      Answering-CAR (aCAR):  A CAR is the source of authority for one or
         more EID prefix to RLOC mappings which which it has been
         administratively configured, and responds to Map Requests for
         these EID-to-RLOC mappings.  Each aCAR provides to parent CDRs
         a list of prefixes that it is responsible for, but not the
         mappings themselves.

         In particular, aCARs peer with CDRs to propagate aggregated
         information about how to find a particular EID-to-RLOC mapping
         upward (but importantly, not the mapping itself).  However,
         aCARs do not peer with other CARs.  The primary difference
         between the aCAR and CDR is that a CAR maintains two databases:
         A EID-to-RLOC mapping database, and a EID-prefix database.  A
         CDR maintains only an EID-prefix database.

      Querying-CAR (qCAR):  A CAR that generates Map-Request messages on
         behalf of one or more of its ITR peers (see below).  Note that
         qCAR has peering connections with ITRs whereas an aCAR does not
         have to.  Finally, both functionalities (qCAR and aCAR) MAY be
         co-located in the same device.  In particular, qCAR MUST also
         be an aCAR, while an aCAR need not be a qCAR.

   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.

   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

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      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.
      ITRs may also have TCP connections to qCARs in order to send
      mapping requests and receive replies (noting that a qCAR, an aCAR,
      and an ITR may be co-located).

3.3.  Relationship Between LISP-CONS Network Elements

   Each LISP-CONS device is known by a single identifier, which is used
   for peering from all peers, and in path-vector (PV) lists.  This
   identifier MAY be an IP address.  An implementation SHOULD use a
   loopback address for this purpose.  Note that this address MUST be
   routable by the core routing system.

   LISP-CONS network elements peer with each other in one of three
   peering relationships: parent, child, or sibling.  The relationship
   is carried in the LISP-CONS OPEN message (see [LISP]).  The permitted
   peering relationships are as follows:

   o  ITRs exist at lowest (unnumbered) level in the peering hierarchy,
      and peer only with one or more CARs.  An ITR MUST NOT peer with
      another ITR or with a CDR.

   o  CARs exist at level 0 in the peering hierarchy, and peer only with
      parent CDRs or with a child ITR.  A CAR MUST NOT peer with another
      CAR; this rule allows the aCARs to aggregate EID prefixes as low
      in the hierarchy as possible.  Note that this rule also means that
      mapping requests and replies are routed over the peering topology,
      not directly between the CARs.

   o  CDRs exist at level 1 (and above) and aggregate EID-prefixes learn
      from its aCAR peerings.  When a two CDRs start their peering
      connection, if one is a parent, the other MUST BE a child.
      Otherwise, they both MUST BE siblings.

   o  If any of these checks fail, the peering connection MUST NOT be

4.  Overview of Operation

   LISP-CONS constructs a multi-level content distribution overlay which
   achieves scalability by imposing a strict aggregation hierarchy on
   the participating elements.  The LISP-CONS hierarchy consists of ITRs

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   the bottom of the hierarchy, CARs at level 0, and CDRs at levels 1
   and above; this is depicted in Figure 1.  Each level of the hierarchy
   is a strict tree.  That is, there are no transit loops in the
   hierarchy; redundancy is achieved by meshing CDR connectivity within
   in a single level of the hierarchy, and the LISP-CONS protocol
   assures that message flow is loop-free.

   In LISP-CONS, the EID-to-RLOC mappings are held in the aCARs, while
   the CDRs maintain information about how to find the aCAR holding a
   particular EID-to-RLOC mapping.  That is, the Push-Add and Push-
   Delete messages (see [LISP]) only contain EID-prefixes (i.e.,
   Locator-sets are not included in these messages and are not stored in
   the CDRs).

   In general, LISP-CONS uses network element redundancy to avoid
   mapping database inconsistencies that may arise in those cases in
   which a CAR or CDR crashes.  Similarly, connectivity outages are
   avoided by configuring a redundant underlying topology.

                 | CDR ------ CDR |
                   /            \
                  /              \
    +----------------+         +----------------+
    | CDR ------ CDR |         | CDR ------ CDR |   (CDR-mesh at level 2)
    +--|----------|--+         +--|----------|--+
       |          |               |          |
       |          |               |          |
   +---|----------|----+      +---|----------|---+
   |  CDR ------ CDR   |      |  CDR ------ CDR  |
   |   |          |    |      |   |          |   |  (CDR-Mesh at level 1)
   |   |          |    |      |   |          |   |
   |  CDR ------ CDR   |      |  CDR ------ CDR  |
   +---|----------|----+      +---|----------|---+
       |          |               |          |
       |          |               |          |
       |          |               |          |
     qCAR       aCAR            aCAR        aCAR
      / \        / \
     /   \      /   \

                       Figure 1: LISP-CONS Hierarchy

   Figure 2 depicts the details of the first three levels of hierarchy.

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   Note that there are no horizontal TCP connections between the ITRs or
   between the CARs.  Note that qCARs (abbreviated "Req-CAR") peer with
   the ITRs, while the aCARs may not.  The CDRs at level 1 are meshed so
   that the two aCARs can aggregate to the same mesh level.

   Note that to avoid request and reply black-holes, all CDRs that are
   responsible for a segment of the address space must be siblings
   (i.e., at the same level).

                             CDR --- CDR (level-1)
                              |\     /|
                              | \   / |
                              |  \ /  |
                              |   X   |
                              |  / \  |
                              | /   \ |
                              |/     \|
                             CAR     CAR (level-0)
                              |\     /|
                              | \   / |
                              |  \ /  |
                              |   X   |
                              |  / \  |
                              | /   \ |
                              |/     \|
                             ITR     ITR

                   Figure 2: LISP-CONS Hierarchy Detail

   LISP-CONS operates as follows: An aCAR receives EID-to-RLOC mappings
   by administrative configuration.  The aCARs aggregate these EID-
   prefixes into power-of-two less specific EID-prefixes, and "push" the
   aggregated EID-prefixes to their (parent) CDRs in Push-Add messages
   (see [LISP]).  CDRs then flood the Push-Add messages to their sibling
   CDRs.  Note that the Push messages contain EID-prefix reachability
   information, not locator sets.

   If a CDR is a child, it then pushes the aggregate for the EID-prefix
   (i.e., the aggregate that "covers" the EID-prefix) to its parent
   CDRs.  This CDR MUST also originate the default EID-prefix
   or 0::0/0 (this allows Requests and Replies to flow up and down the
   aggregation hierarchy).  This default is contained within the level
   of the sibling mesh.  Note that aggregates MUST only be generated
   when the components of the aggregate are all longer prefixes than the
   aggregate (and importantly, NOT equal in length).  For example, a CDR
   MUST NOT generate an aggregate such as A.B.0.0/16 if it has not heard
   a A.B.*.0/24 from either a child or sibling peer.

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   When an ITR needs a mapping, it sends a Map-Request message to its
   directly connected qCARs.  If any of those CARs have cached the
   requested mapping, the result is immediately returned to the ITR.
   Otherwise, the Map-Request message is routed through the CDR
   hierarchy to the aCAR which holds the mapping.  That CAR then returns
   the mapping in a Map-Reply message (which is routed over the peering
   topology) to the qCAR, which then forwards it on to the requesting

   Finally, note that this type of advertisement hierarchy allows EID
   lookups to have lower Round Trip Times (RTTs) when the EID-prefix is
   "close" (in the EID allocation hierarchy) to the site's attached CAR.
   However, for scalability reasons, a request may have to travel extra
   hops to get an EID-prefix that can only be obtained by going up the
   tree (and in the worse case, by going to the top of the hierarchy and
   down to the aCAR that hold the mapping).

5.  The LISP-CONS Protocol

   This section describes the LISP-CONS protocol in detail, starting
   with how LISP-CONS builds a distributed mapping database, how an ITR
   queries the database, and how the database is maintained.

   LISP-CONS operates on three different data structures:

   EID-to-RLOC Database:  The EID-to-RLOC mapping database, which is
      administratively configured and held in the aCARs.

   Mapping Cache:  The Mapping Cache (hereafter cache) is the result of
      a Map-Request and is stored in the ITRs and qCARs.

   EID-Prefix Table:  The EID-Prefix table is used to route Map-Requests
      and Map-Replies in the overlay network.  It is stored only by
      CDRs, and associates an EID-prefix with a 64-bit sequence number,
      a path-vector, and a priority and weight (to facilitate later
      aggregation, if possible).

5.1.  Building the LISP-CONS Database

   When an aCAR is configured with an EID-to-RLOC mapping, it checks to
   see if it can aggregate the just learned EID-prefix with any of the
   other EID-prefixes it has been configured with.  The CAR then sends
   ("pushes") the EID-prefix (or an aggregate, if possible) to its
   parent CDR in a Push-Add message.

   An aCAR generates an aggregate when it has at least one more specific
   prefix that matches the aggregate.  A more specific prefix of an

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   aggregate is when the high-order bits of the more-specific prefix and
   the high-order bits of the aggregate are the same.  The number of
   bits tested is the mask-length of the aggregate.

   When a more-specific prefix is added to the EID-prefix table, the
   corresponding aggregate is sent in a Push-Add message from a child
   peer to a parent peer in a different level.

   Push-Add messages contain an EID-prefix, and Originator Address, a
   64-bit sequence number, and a PV that records the path the message
   took in the CDR level (see [LISP]).  Note that the Originator Address
   is an EID used to route a Reply back to the requesting ITR The PV
   list will always contain Locators.

   When a CDR receives a Push-Add message, it first checks to see if the
   sequence number for the EID-prefix is numerically larger than what it
   has stored for the EID-prefix.  If it is not, the message is dropped.
   Otherwise, the CDR next checks for its own address in the PV.  If it
   exists, the message is discarded.  Otherwise, the CDR stores EID-
   prefix and the associated PV.  Note that the CDR can store all
   different combination of PVs or just the shortest path ones.  If the
   CDR has one or more parent peerings configured (i.e., the CDR is a
   child), it will aggregate this EID-prefix with other EID-prefixes
   into a more coarse EID-prefix.  The CDR does not need to advertise
   anything to lower-level CDRs because child peers will auto-generate a
   default EID-prefix into their level simply due to having a child-
   parent peering relationship.

   When a CDR sends a Push-Add message to a parent, the stored PV is not
   propagated to the parent in the aggregated EID-prefix; rather, it
   includes a one element PV which contains the address of the CDR
   originating the "aggregated push".  It also includes a new sequence
   number, indicating that this is a different EID-prefix than the ones
   it has stored.

   Finally, if a CDR is a child, it pushes a "EID-default" to its
   siblings.  This Push message has EID-prefix or 0::0/0 and a
   PV containing the address of the CDR that is sourcing the default.

5.2.  Querying the LISP-CONS Database

   Map Requests are routed along the LISP-CONS multi-level topology from
   requesting ITR to aCAR holding the requested mapping.  The Map-
   Request message includes a PV which records the route traversed by
   the Map-Request message.  This PV is used to control request routing
   and for debugging purposes.

   When an ITR wants to query the LISP-CONS database for a mapping, it

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   prepares a Map-Request message, which is sent to one of its directly
   connected qCAR(s).  The Map-Request message is routed over the
   peering topology to the aCAR that holds the mapping.  If the qCAR has
   cached the mapping (perhaps from a previous request), in which case
   it returns the mapping immediately.

   When a qCAR receives a Map-Request from from an ITR, it MAY respond
   immediately if it has the cached requested mapping.  Otherwise, it
   MUST forward the Map-Request message to its parent CDRs.  This CAR is
   identified by the Originator address in the Map-Request message (see
   [LISP]).  The Originator address allows a replying CDR to forward a
   No-Map message (see [LISP]) back to the qCAR.  This case arises when
   source-site is LISP-enabled (i.e., there is an ITR deployed), but the
   destination-site has not deployed LISP yet so there is no ETR.

   When a Map-Request arrives at a CDR, the CDR first scans its PV for
   its address.  If its address is present, it drops the packet.  If its
   address is not present, it consults its EID-prefix table for the
   longest match "next-hop" towards the aCAR holding the mapping for the
   prefix.  If a next-hop is found, the CDR appends its address to the
   PV, and forwards the Request to the next-hop.

   When a Map-Request arrives at a CDR which cannot route it, a LISP-
   CONS No-Map message (see [LISP]) MUST BE sent back to the qCAR.  This
   No-Map message is a signal that indicates that there is no mapping
   for the requested EID in the system, and is immediately communicated
   to the ITR.

   When a Map-Request message arrives at an aCAR, it first queries its
   mapping database for the EID contained in the Map-Request message.
   If the mapping is found, it constructs a Map-Reply message (see
   [LISP]) containing the EID, the corresponding RLOC-set, and an PV
   containing its address appended to the reverse of the received PV.
   The CAR then sends the Map-Reply message over the peering topology to
   the qCAR (i.e., to the Originating CAR EID-Prefix in the Map-Request

   If no mapping is found, the aCAR sends a Map-Reply with the requested
   EID and a Locator count of 0 back to qCAR.  This creates a negative
   cache entry in the requesting ITR.

   In LISP-CONS, the PV for Map-Request and Map-Reply messages are
   preserved across the hierarchy, while the PV lists carried in Push-
   Add and Push-Delete messages are not.  As a result, LISP-CONS also
   has cross-level loop suppression.

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5.3.  Maintaining the LISP-CONS Database

   While LISP-CONS is not a routing protocol (and as such when peering
   connections go down EID-prefix entries are not immediately withdrawn
   from the local EID-prefix table), it does uses a link-state-like
   sequence number scheme to detect changes in topology.  Similarly,
   LISP-CONS uses a path vector scheme to detect and suppress message
   looping.  There are four database maintenance cases to consider:

   o  An EID-Prefix Is Administratively Removed From The Infrastructure
      (Section 5.3.1)

   o  A CAR's Connectivity Changes (Section 5.3.2)

   o  A CAR Becomes Unreachable (Section 5.3.3)

   o  A CDR Becomes Unreachable (Section 5.3.4)

   Each case is considered below.

5.3.1.  An EID-Prefix Is Administratively Removed From The

   EID-prefix mappings are removed from the LISP-CONS infrastructure by
   administrative configuration at the aCAR that was configured with the
   mapping.  The CAR queries its EID-prefix database for the mapping.
   If no match for the EID-prefix exists, no further action is taken.

   When all the more-specific prefixes that matches the aggregate are
   removed from the EID-prefix table, the aggregate is sent in a Push-
   Delete message from a child peer to a parent peer in a different
   level.  The Push-Delete message behaves exactly like the Push-Add
   message, except that it removes the corresponding state along its

   When a Push-Delete message arrives at a CDR, the CDR checks for its
   own address in the PV.  If it exists, the message is discarded.
   Otherwise, the CDR queries its EID-prefix database for the EID-prefix
   in the received Push-Delete message.  If it finds a matching entry,
   it removes the entry from its database, appends its address to the
   PV, and forwards the message to its siblings.

   If the CDR is a child, it checks to see if the EID-prefix in the
   Push-Delete message is the last in an aggregate it had previously
   pushed to its parent CDR.  If not, no further action is taken.
   Otherwise, the CDR computes a new aggregate (minus the prefix from
   the Push-Delete), sends a Push-Delete for the old aggregate to its
   parent, and sends a Push-Add with the new aggregate to its parent

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5.3.2.  A CAR's Connectivity Changes

   Changes in CAR connectivity are signaled by changes in the sequence
   numbers in a Push-Add messages.  For example, in Figure 3, consider
   the case in which the D<->B TCP connection breaks.  In this case, D
   sends a Push-Add with EID-Prefix EID/(n-1), sequence number, S+1, and
   path vector [D] (denoted push(EID/(n-1), S+1, [D])) to C. C
   aggregates the pieces of EID and forwards push(EID/n,S+1,[C,D]) to B.
   Now, before the failure, B had an entry in its EID-prefix table for
   EID/n with sequence number S and PV [D].  Since B sees a new push
   message originated by D with sequence number S+1, it knows the
   previous entry (EID/n,S,[D]) is no longer valid.

   Similarly, A will see push messages with both [C,D] and [B,C,D] and
   with sequence number S+1, so it knows the existing entries ([B,D] and
   [C,B,D], with sequence number S) are both obsolete.

                                   /     \
                          ^       /       \       ^
                          |      /         \      |
    push(EID/n,S,[B,C,D]) |     /           \     | push(EID/n,S,[C,D])
                               /    CDR      \
    push(EID/n,S,[A,C,D]) |   /     mesh      \   | push(EID/n,S,[A,B,C,D])
                         \|/ /                 \ \|/ (will be discarded)
                            /                   \
                           /                     \
                           \ push(EID/n,S,[C,D]) /
                         ^  \    <---------     / ^
                         |   \                 /  |
      push(EID/n,S,[D])  |    \               /   | push(EID/n,S,[D])
                         |     \             /    |
                                \           /
                                 \         /
                                   D (CAR)   Configure EID/(n-1), RLOC-set
                                    F (ETR)

                   Figure 3: Sequence Number Processing

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5.3.3.  A CAR Becomes Unreachable

   If the TCP connection between a CAR its peer CDR drops, a timer
   associated with the EID-prefix received from the CAR in the Push-Add
   message is started.  The timer, called the CAR-CDR-TCP-TIMER, is set
   to a default value of 60 minutes.

   If the TCP connection comes back up before the timer expires, the
   timer is stopped and no further action is taken.

   If the timer expires, the CDR builds a Push-Delete message for each
   EID-prefix it received from the aCAR, and sends the Push-Delete to
   its siblings.  The Push-Delete message contains the EID-prefix to be
   removed, a sequence number, and PV containing only the CDR's address.

   If the CDR also has a parent peering, it checks to see if any of the
   EID-prefixes it received from a child peering were the last more
   specific prefix in an aggregate it previously pushed to a parent CDR.
   If not, no further action is taken.  If so, it sends a Push-Delete
   for the aggregate to its parent(s).  In either case, the CDR deletes
   the entries received from the failed CAR from its EID-prefix table.

5.3.4.  A CDR Becomes Unreachable

   There are three cases to consider here: A sibling CDR peering goes
   down, a parent peering goes down, and an child peering goes down.
   Each is considered below.  A Sibling CDR Becomes Unreachable

   When the TCP connection drops between a CDR and a sibling CDR, a
   timer associated with the EID-prefixes received from the sibling CDR
   in the Push-Add message is started.  This timer, called CDR-SIBLING-
   TCP-TIMER, defaults to TBD.

   If the TCP connection comes back up before the timer expires, the
   timer is stopped and no further action is taken.

   If the timer expires, the CDR builds a Push-Delete message for each
   EID-prefix it received from the CDR, and sends the Push-Delete to its
   siblings.  The Push-Delete message contains the EID-prefix to be
   removed, a sequence number, and PV containing only the CDR's address.

   If the CDR also has a parent peering, it checks to see if any of the
   EID-prefixes it received from the failed CDR were the last more
   specific prefix in an aggregate it previously pushed to a parent CDR.
   If not, no further action is taken.  If so, it sends a Push-Delete
   for the aggregate to its parent(s).  In either case, the CDR deletes

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   the entries from its EID-prefix table.  A Parent CDR Becomes Unreachable

   When the TCP connection drops between a CDR and a parent CDR, the
   child starts a timer (the CDR-CDR-TCP-TIMER) associated with the
   parent CDR.

   If the TCP connection comes back up before the timer expires, the
   timer is stopped and no further action is taken.

   If the timer expires, the CDR deletes the EID-prefix entry, and
   builds a Push-Delete message for the default EID prefix and sends it
   to its siblings.  The Push-Delete message contains the EID-prefix or 0::0/0, a sequence number, and PV containing only the
   CDR's address.  A Child CDR Becomes Unreachable

   Since nothing is ever "pushed down", no action needs to be taken when
   a child CDR becomes unreachable.  See Section for the actions
   a child CDR takes when a parent becomes unreachable.

6.  LISP-CONS Message Types

   LISP messages are sent over either UDP or TCP sockets using well-
   known IANA-assigned port number 4342.

   In all message formats, IPv4 or IPv6 addresses can be mixed or match.
   So a payload of IPv6 addresses can be sent over a TCP connection (or
   be UDP encapsulated) that runs over IPv4 and vice-versa.  You can
   also mix EID-to-RLOC mappings.  That is, an IPv6 EID-prefix can have
   a set of IPv4 or IPv6 Locator addresses associated with it and vice-
   versa.  Originator addresses and Path Vector lists can also be mixed
   as well.

   A TCP connection is established by two LISP-CONS peers by having the
   higher IP address side of the connection do a passive-open and the
   lower IP address side to an active open.  This is done to avoid 2
   connections from call colliding.  This is similar to the procedures
   in [RFC3618].

   See [LISP] for packet type value definitions and formats.

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7.  Operational Considerations

   TBD: However, mention that there will be less policy than in BGP.
   That is, information cannot be altered, like a CAR cannot add or
   remove locators, path-vectors can't be made to look longer, etc....

   Future revisions of this document will have a more through
   description of deployment scenarios, once we get some implementation
   and pilot deployment experience.

8.  LISP-CONS and Locator Reachability

   It is important to note that LISP-CONS is designed to as a mapping
   database that defines EID-to-RLOC mappings, where the RLOCs are IP
   addresses of ETRs and does not indicate if the ETRs, or the path to
   the ETRs are up.

   In general, LISP determine reachability through either ICMP No-Map
   messages or LISP data-plane Locator Reach bits that are transmitted
   in LISP Data messages [LISP].

   The design principle underlying LISP-CONS is to keep the mapping
   database service scalable.  As such, the design discourages high
   frequency changes in mappings.

9.  LISP-CONS and Mobility

   The mapping database does not convey Foreign Agent locator addresses.
   This can be achieved in the data plane but will be documented in
   another Internet Draft.

10.  Open Issues

   o  Do we need a Close Message? (dual of open).  Otherwise EID-
      prefixes may not get removed until a timeout.

   o  No mapping exists in the ITR: You have a configuration option to
      either 1) drop the packet, or 2) do LISP 1.5 where the packet is
      routed on another topology.  The other option is to allow the ITR
      get a push of or 0::0/0 from its peering CARs (or have
      it configured in the ITR).

   o  Security Section: We need to finish the evaluation of
      vulnerabilities.  Map vulnerabilities against security mechanisms.
      At first blush, the real outstanding question remaining (as you

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      note in your notes above) is transitive message security (ala dns-

   o  Security Model: Is the implied transitive trust sufficient?

   o  From http://ana-3.lcs.mit.edu/~jnc/tech/lisp/optimizations.txt:

      Caching of bindings in the CDR hierarchy:  This is such a win, it
         gives you a system which is almost as fast as a 'push' system,
         but without the overhead of giving updates to people who don't
         need them

      'Piggybacking' of client bindings when a request is made:  This
         will greatly increase the speed of responses for everyone, big
         and small; it is a considerably more complex optimization than
         any other, but the payoff is so significant I think it's
         probably worth it

      Direct reply to queries via UDP:  This optimizes response time to
         cache misses on qCARs; not a big gain in performance, but it's
         very simple to do, so worth it overall

      Push of 'delegation' info (actually, advertisments):  This will
         minimize the path length for requests traversing the server
         pseudo-hierarchy; it needs a good heuristic algorithm to limit
         the distance upwards, which I haven't seen yet (but feel
         confident we can come up with)

      Direct notification of outdated bindings:  This is needed to make
         caching of bindings work

11.  Acknowledgments

   Many of the ideas described in this document developed during
   detailed discussions with Eliot Lear, Mark Handley, and Dave Oran.
   Robin Whittle also made several insightful comments on earlier
   versions of this document.

12.  Security Considerations

   LISP-CONS is a straightforward protocol to secure.  Its combination
   of simplicity, explicit peering, and explicit configuration provides
   for a well understood set of relationships between elements.  Its
   security mechanisms are comprised of existing technologies in wide
   operational use today.

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   As a hybrid push-pull protocol, LISP-CONS shares some of security
   characteristics of pull (DNS) and push (BGP) protocols.  Securing
   LISP-CONS is much simpler than either of those examples however.
   Compared to DNS, the fact that messages traverse a explicit hierarchy
   of TCP connections, and the message make-up itself makes LISP-CONS
   less susceptible to denial of service and amplification attacks.
   Compared to BGP, LISP-CONS CDRs are not topologically bound, allowing
   them to be put in locations away from the vulnerable AS border
   (unlike eBGP speakers).

12.1.  Apparent LISP-CONS Vunerabilities

   This section briefly lists of the apparent vulnerabilities of LISP-

   Mapping Integrity:  Can you insert bogus mappings to black-hole
      (create a DoS) or intercept LISP data-plane packets?

   CAR Availability:  Can you DoS the aCAR(s) holding the mappings for a
      particular ETR?  Without access to its 1-2 available CAR(s) an ITR
      has no ability to connect to the rest of the Internet.

   ITR Mapping/Resources:  Can you force an ITR to drop legitimate
      mapping requests by flooding it with random destinations that it
      will have to query for?  Seems like a problem with any pull based
      system (DNS has this problem).  Is this an ITR implementation
      issue, or is there a way we can assist ITR implementers here in
      the LISP-CONS spec?

   Path Vector Exploits for Reconnaissance:  Can you learn about the
      LISP topology by sending legitimate mapping requests messages and
      then observing the path-vector information.  Is this information
      useful in attacking or subverting peer relationships?  Not data
      plane but control plane service - this vulnerability seems unique
      to LISP-CONS.  ITRs cannot do this, since they don't have access
      to the PVs (the PVs aren't sent along to the ITRs).  Note that
      LISP has a similar data-plane reconnaissance issue.

   Scaling of CAR/CDR Resources:  Can you flood the system with requests
      or replies due to the limited capacity of the control plane?  TCP
      prevents anycasting to add capacity, and one of the issues has to
      be how do we scale if we need to?

12.2.  Survey of LISP-CONS Security Mechanisms

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   Use of Device Loopbacks:  From levels 0 to 1 (or n) in the topology,
      these loopbacks should come from known infrastructure subnets (as
      do say BGP peers) that should allow for some isolation via Access
      Control Lists (ACLs) and anti-spoofing mechanisms.

   Explicit Peering:  The devices themselves can both prioritize
      incoming packets as well as potentially do key checks in hardware
      to protect the control plane.

   Use of TCP to Connect Loopbacks:  This makes it difficult for third
      parties to inject packets.

   Use of HMAC Protected TCP Connections:  HMAC is used to verify
      message integrity and authenticity, making it nearly impossible
      for third party devices to either insert or modify messages.

   Message Sequence Numbers and Nonce Values in Messages:  This allows
      for devices to verify that the mapping-reply packet was in
      response to the mapping-request that they sent.

   Path Vectors:  Path Vectors prevent arbitrary messages from
      traversing the topology, and raise the bar for spoofing/invalid
      Path-Delete messages.

13.  IANA Considerations

   This document creates no new requirements on IANA namespaces

14.  References

14.1.  Normative References

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

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

   [RFC3618]  Fenner, B. and D. Meyer, "Multicast Source Discovery
              Protocol (MSDP)", RFC 3618, October 2003.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.

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   [LISP]     Farinacci, D., Fuller, V., Oran, D., and D. Meyer,
              "Locator/ID Separation Protocol (LISP)",
              draft-farinacci-lisp-05 (work in progress), November 2007.

14.2.  Informative References

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

              Meyer, D., "Report from the IAB Workshop on Routing and
              Addressing", draft-iab-raws-report-02 (work in progress),
              April 2007.

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

Authors' Addresses

   Scott Brim

   Email: sbrim@cisco.com

   Noel Chiappa

   Email: jnc@mercury.lcs.mit.edu

   Dino Farinacci

   Email: dino@cisco.com

   Vince Fuller

   Email: vaf@cisco.com

   Darrel Lewis

   Email: darlewis@cisco.com

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   David Meyer

   Email: dmm@cisco.com

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