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Versions: 00 01 02 draft-ietf-lisp-interworking

Network Working Group                                           D. Lewis
Internet-Draft                                                  D. Meyer
Intended status: Experimental                               D. Farinacci
Expires: June 7, 2008                                Cisco Systems, Inc.
                                                        December 5, 2007


                  Interworking LISP with IPv4 and IPv6
                    draft-lewis-lisp-interworking-00

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   This Internet-Draft will expire on June 7, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes various methods for interworking between the
   Internet and an Internet in which Endpoint Identifiers are separated
   from to Routing Locators using the Locator/ID Separation Protocol
   (LISP).  Existing Internet hosts that do not participate in the LISP
   system must still be able to reach sites numbered from this EID
   prefixes.  This new draft describes mechanisms which might be used to
   provide reachability between these types of sites.  A new network



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   element, the Proxy Tunnel Router may also be deployed to act as a
   transitional LISP Ingress Tunnel Router for a subnetwork which does
   not implement LISP but which requires communication to devices that
   are addressed from LISP prefixes.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  LISP Interworking Models . . . . . . . . . . . . . . . . . . .  3
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  4
   4.  Routable EIDs  . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Impact on Routing Table  . . . . . . . . . . . . . . . . .  6
     4.2.  Requirement for using BGP  . . . . . . . . . . . . . . . .  6
     4.3.  Limiting the Impact of Routable EIDs . . . . . . . . . . .  6
     4.4.  Use of Routable EIDs for Testing LISP  . . . . . . . . . .  6
   5.  Proxy Tunnel Routers . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  PTR EID announcements  . . . . . . . . . . . . . . . . . .  7
     5.2.  Packet Flow with PTRs  . . . . . . . . . . . . . . . . . .  7
     5.3.  Scaling PTRs . . . . . . . . . . . . . . . . . . . . . . .  8
     5.4.  Impact of the PTRs placement in the network  . . . . . . .  9
     5.5.  Benefit to Networks Deploying PTRs . . . . . . . . . . . .  9
   6.  LISP-NAT . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  LISP-NAT for LISP-NR addressed hosts . . . . . . . . . . . 10
     6.2.  LISP Sites with Hosts using RFC 1918 Addresses Sending
           to non-LISP Sites  . . . . . . . . . . . . . . . . . . . . 11
     6.3.  LISP Sites with Hosts using RFC 1918 Addresses
           Communicating to Other LISP Sites  . . . . . . . . . . . . 11
     6.4.  LISP-NAT and multiple EIDs . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  IANA Considersations . . . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 15














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1.  Introduction

   This document describes methods for transitioning from today's
   Internet to a future Internet in which Endpoint Identifiers (EIDs)
   are separated from to Routing Locators (RLOCs) using the Locator/ID
   Separation Protocol (LISP) [LISP].

   A key behavior of this separation that EID prefixes are not
   advertised to the Internet's Default Free Zone (DFZ).  In particular,
   only RLOCs are carried in the DFZ.  Existing Internet hosts who do
   not participate in the LISP system must still be able to reach sites
   numbered from this non routed EID space.  This draft describes a set
   of mechanisms which can be used to provide reachability between sites
   that are LISP-capable and those which are not.  A new LISP network
   element, the Proxy Tunnel Router (PTR) (Section 5) may also be
   deployed to act as a LISP Ingress Tunnel Router (ITR) for a site
   which does not implement LISP but which requires communication to
   devices that are using LISP prefixes advertised into the DFZ.

   Note that any successful interworking model should be agnostic to any
   particular EID-to-RLOC mapping algorithm.  This document does not
   comment on the value of any of the particular mapping system.

   The remainder of this document is organized as follows: Section 2
   describes the internetworking models considered in this document.
   Section 3 defines terms used throughout this draft.  Section 4
   describes the relationship of the EID space and the current Internet.
   Finally, Section 5 and Section 6 introduce mechanisms which provide
   successful interworking between the two systems.


2.  LISP Interworking Models

   There are 4 unicast connectivity cases which describe how sites can
   communicate with each other:

   1.  Non-LISP site to Non-LISP site

   2.  LISP site to LISP site

   3.  LISP site to Non-LISP site

   4.  Non-LISP site to LISP site

   The first case is the Internet as we know it today and as such will
   not be discussed further here.  The second case is documented in
   [LISP] and hence there are no new interworking requirements (since
   there are no new protocol requirements placed on intermediate non-



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   LISP routers).

   Cases 3 and 4, while seemingly similar, are subtly different and are
   explained below.

   In case 3 (LISP site to Non-LISP site), a LISP site can send packets
   to a non-LISP site because the non-LISP site prefixes are routable.
   The non-LISP site need not do anything new to receive packets.  The
   only action the LISP site needs to take is to know when not to LISP-
   encapsulate packets.  This can be achieved via two mechanisms:

   1.  First, at the ITR in the source site, if the destination of an IP
       packet is found to match a prefix from the BGP routing table,
       then the site is directly reachable by the BGP core that exists
       and operates today.

   2.  Second, if (from the perspective of the ITR at the source site)
       the destination address of an IP address is not found in the EID-
       to-RLOC mapping database, the ITR could infer that it is not a
       LISP-capable site, and decide to not LISP-encapsulate the packet.

   The most challenging case, case 4, occurs when a host at a non-LISP
   source site sends a packet to a host in a LISP site.  If the source
   host chooses a non-routable EID address, the packet continue to be
   forwarded (inside the domain) until it reaches a router which cannot
   forward it, at which point the packet is dropped.  So either the EID
   that the destination site is making available for other sites is
   routed outside of LISP or an alternate mechanisms need to be in place
   to solve this.

   This specification describes two alternate interworking mechanisms,
   Proxy Tunnel Router (PTR) (Section 5) and LISP-NAT (Section 6).


3.  Definition of Terms

   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 LISP headers are prepended only when the packet
      reaches an Ingress Tunnel Router (ITR) on the data path to the
      destination EID.

   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 length.




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   Routing Locator (RLOC):  An IP address of a LISP tunnel router.  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 and 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 an 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.

   EID Prefix Reachability:  An EID prefix is said to be "reachable" if
      one or more of its locators are reachable.  That is, an EID prefix
      is reachable if the ETR (or its proxy) is reachable.

   Default Mapping:  A Default Mapping is a mapping entry for EID-prefix
      0.0.0.0/0.  It maps to a locator-set used for all EIDs in the
      Internet.  If there is a more specific EID-prefix in the mapping
      cache it overrides the Default Mapping entry.  The Default Mapping
      route can be learned by configuration or from a Map-Reply message
      [LISP].

   LISP Routable (LISP-R) Site:  A LISP site who's addresses are used as
      both globally routable IP addresses and LISP EIDs.

   LISP Non-Routable (LISP-NR) Site:  A LISP site who's addresses are
      EIDs only, these EIDs are not found in the legacy Internet routing
      table.

   LISP Proxy Tunnel Router (PTR):  PTRs are used to provide
      interconnectivity between sites which use LISP EIDs and those
      which do not.  They act a gateway between the Legacy Internet and
      the LISP enabled Network.  A given PTR advertises one or more
      highly aggregated EID prefixes into the public Internet and acts
      as the ITR for traffic received from the public Internet.  LISP
      Proxy Tunnel Routers are described in Section 5.

   LISP Network Address Translation (LISP-NAT):  Network Address
      Translation between EID space assigned to a site and RLOC space
      also assigned to that site.  LISP Network Address Translation is
      described in Section 6.

    EID Sub Namespace:  A power-of-two block of aggregatable locators
      set aside for LISP interworking.






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4.  Routable EIDs

   An obvious way to achieve interworking between LISP and non-LISP
   hosts is to simply announce EID prefixes into the DFZ (much like
   today's Provider Independent (PI) addresses are).  Of course, making
   EIDs routable in this way is not desirable as it has the potential to
   increase the size of the DFZ table rather than reduce it size (a
   primary goal of LISP).

4.1.  Impact on Routing Table

   If EID prefixes are announced into the DFZ, the impact is similar to
   the case in which LISP has not been deployed, since these EID
   prefixes will not be any more aggregatable than existing PI
   addressing.  This behavior is not desirable, and such a mechanism is
   not viewed as a viable long term solution.

4.2.  Requirement for using BGP

   Non-LISP sites today use BGP to (among other things) enable ingress
   traffic engineering.  Relaxing this requirement is another primary
   design goal of LISP.

4.3.  Limiting the Impact of Routable EIDs

   Two schemes are proposed to limit the impact of having EIDs announced
   in the current global Internet routing table:

      Section 5 discusses the LISP Proxy Tunnel Router, an approach that
      provides ITR functionality to bridge LISP-capable and non-LISP-
      capable sites.

      Section 6 discusses another approach, LISP-NAT, in which NAT
      [RFC2993] is combined with ITR functionality to limit the the
      impact of routable EIDs on the Internet routing infrastructure.

4.4.  Use of Routable EIDs for Testing LISP

   Given one of the primary design goals for LISP (and other Locator/ID
   separation schemes) is to be able to take advantage of topological
   aggregation of addresses.  Note that since a primary design goal of
   LISP is to see benefits of aggregation as soon as possible, it is
   highly desirable to remove EID-prefixes from the global routing
   system.

   That being said, sites that are using PA address blocks that are
   aggregated by their service provider, can use these addresses as EIDs
   without disadvantage to the the routing system (i.e., no additional



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   prefixes need to be advertised into the DFZ).  In this case,
   interworking from a LISP site with PA addresses to a non-LISP site
   can easily be achieved, since such addresses are already routable.
   However, as mentioned above, it is a design goal of LISP to reduce
   the size of the DFZ routing table, and as such if follows that
   removal of EID prefixes (of any kind) from the DFZ follows is also a
   goal.


5.  Proxy Tunnel Routers

   Proxy Tunnel Routers (PTRs) allow for non-LISP sites to communicate
   with LISP-NR sites.  PTRs have two primary functions:

   Originating EID Advertisements:  PTRs advertise highly aggregated
      EID-prefix space on behalf LISP sites to non-LISP sites can reach
      such LISP sites.

   Encapsulating Legacy Internet Traffic:  PTRs also encapsulate non-
      LISP Internet traffic into LISP packets and route them towards
      their destination RLOCs.

5.1.  PTR EID announcements

   A critical characteristic of PTR functionality is to advertise
   aggressively aggregated EID-prefixes.  Not only can the number of
   advertised routes be minimized, but in addition the number of places
   where the EID-prefix routes are stored can also be reduced by careful
   PTR placement.  Rather than deploying PTRs close the LISP sites, they
   get deployed close to the non-LISP sites.  In this way, load can be
   spread among many PTRs while at the same time as scoping the EID-
   prefix advertisements.

5.2.  Packet Flow with PTRs

   Packets from non-LISP sites can reach LISP-NR sites by the aid of
   PTRs.  Packets from non-LISP sites traverse the Internet until
   reaching a PTR, where they are encapsulated.  Once encapsulated, the
   packets use the LISP (outer) header's destination address in order to
   reach the destination's ETR.

   Following is an example of the path a packet would take when using a
   PTR.  In this example, the LISP-NR site is given the EID prefix of
   140.0.0.0/24.  Lets us also say, for the purposes of this example,
   that this prefix, or a larger aggregate is not found in today's
   Internet routing system.  In other words, if a packet with this
   destination reached a router in the Default Free Zone, it would be
   dropped.  In this example PTR is configured to announce this route



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   (very likely a much larger aggregate), and so sink the traffic to the
   PTR.

   1.  Host makes a DNS lookup EID for destination, and gets 140.1.1.1
       in return.

   2.  Host has a default route to customer Edge (CE) router and
       forwards the packet to the CE

   3.  The Site's CE has a default route to its Provider Edge (PE)
       router, and forwards the packet to the PE.

   4.  The PE has route to 140.0.0.0/24 and the next hop is the PTR.

   5.  The PTR has a mapping for 140.0.0.0/24 and LISP encapsulates, the
       packet now has a destination address of the RLOC.

   6.  PTR looks up the RLOC, and forwards LISP packet to the next hop.

   7.  The ETR decapsulates the packet and delivers the packet to the
       140.1.1.1 host in the destination LISP site.

   8.  Packets from host 140.1.1.1 will flow back through the LISP
       site's ITR.  In this case, the packet is not encapsulated because
       the ITR knows the destination is a non-LISP site so the packet is
       delivered natively and directly to the destination site (i.e. the
       PTR does not get return traffic)

   Note that in this example the return path is asymmetrical, so return
   traffic will not go back through the PTR.  This is because the
   LISP-NR site's ITR will discover that the originating site is not a
   LISP site, and not encapsulate the returning packet (see [LISP] for
   details of ITR behavior).

   Alternatively, return traffic could be symmetrical.  There are two
   cases in which traffic could be symmetrical:

   1.  The ETR in the LISP site gleans the PTR's RLOCs for the EID, and

   2.  The PTR could put the non-LISP site's prefix in the mapping
       database and use itself and a partner PTR as the RLOCs.

5.3.  Scaling PTRs

   PTRs sink traffic by announcing the LISP EID namespace.  There are
   several ways that an network could control the way traffic reaches a
   PTR in order to prevent a given PTR from receiving more traffic than
   it has the capacity to handle.



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      First, the PTR's aggregate routes might be selectively announced
      in order to have a course way to control the typical amount of
      traffic sent towards a particular PTR.

      Second, the same address might be announced by multiple PTRs in
      order to share the traffic by using the IP Anycast technique.  The
      asymmetric nature of traffic flows allows for the PTR to be
      relatively simple - it will only have to encapsulate LISP packets.

5.4.  Impact of the PTRs placement in the network

   There are several that a network using PTRs would place the PTR as
   close as possible to non-LISP sites.  First, placing the PTR near the
   ingress of traffic allows for the communication between the non-LISP
   site and the LISP site to have the last amount of stretch.

   Some proposals (see for example CRIO [CRIO]) have suggested grouping
   PTRs near an arbitrary subset of ETRs and announcing a 'local' subset
   of EID space.  This model cannot guarantee minimum stretch (the ratio
   of actual path length to optimal path length) if there are changes to
   where EIDs are injected into the system (for example, if a site
   changes ISPs).

5.5.  Benefit to Networks Deploying PTRs

   When traffic destined for LISP-NR site arrives and is encapsulated at
   a PTR, the new (appended) packet header is addressed to the
   destination's RLOC.  One benefit of this behavior is that this
   traffic will be routed towards

   RLOCs and be better able to follow the network's traffic engineering
   policies (such as closest exit routing).


6.  LISP-NAT

   LISP Network Address Translation (LISP-NAT) is a limited form of NAT
   [RFC2993].  LISP-NAT is designed to enable the interworking of non-
   LISP sites and LISP-NR sites by ensuring that the LISP-NR's sites
   addresses are always routable.  LISP-NAT accomplishes this by
   translating a host's source address from an 'inner' value to an
   'outer' value and keeping this translation in a table that it can
   reference for subsequent packets.

   In addition, existing RFC 1918 [RFC1918] sites can use LISP-NAT to
   talk to both LISP or non-LISP sites.

   The basic concept of LISP-NAT is that when transmitting a packet, the



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   ITR replaces a non-routable EID source address with a routable source
   address, which enables packets to return to the site.

   There are two main cases that involve LISP-NAT:

   1.  Hosts at LISP sites that use non-routable global EIDs speaking to
       non-LISP sites using global addresses.

   2.  Hosts at LISP sites that use RFC 1918 private EIDs speaking to
       other sites, who may be either LISP or non-LISP.

   Note that LISP-NAT is not needed in the case of LISP-R (routable
   global EIDs) sources.  This is because the LISP-R source's address is
   routable, and return packets will be able to natively reach the site.

6.1.  LISP-NAT for LISP-NR addressed hosts

   LISP-NAT allows a host with a LISP-NR EID to communicate with non-
   LISP hosts by translating the LISP-NR EID to a globally unique
   address.  This globally unique address may be a either a PI or PA
   address.

   An example of this translation follows.  For this example, a site has
   been assigned a LISP-NR EID of 220.1.1.0/24.  In order to utilize
   LISP-NAT, the site has also been provided the PA EID of
   128.200.1.0/24, and uses the first address (128.200.1.1) as the
   site's RLOC.  The rest of this PA space (128.200.1.2 to
   128.200.1.254) is used as a translation pool for this site's hosts
   who need to communicate with non-LISP hosts.

   The translation table might look like the following:

   Site NR-EID    Site R-EID      Site's RLOC    Translation Pool
   =========================================================================
   220.1.1.0/24   128.200.1.0/24  128.200.1.1    128.200.1.2 - 128.200.1.254

                    Figure 1: Example Translation Table

   The Host 220.1.1.2 sends a packet destined for a non-LISP site to its
   default route (the ITR).  The ITR receives the packet, and determines
   that the destination is not a LISP site.  How the ITR makes this
   determination is up to the ITRs implementation of the EID-to-RLOC
   mapping system used (see, for example [LISP-ALT]).

   The ITR then rewrites the source address of the packet from 220.1.1.2
   to 128.200.1.2, which is the first available address in the LISP-R
   EID space available to it.  The ITR keeps this translation in a table
   in order to reverse this process when receiving packets destined to



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   128.200.1.2.

   Finally, when the ITR forwards this packet without encapsulating it,
   it uses the entry in its LISP-NAT table to translate the returning
   packets' destination IPs to the proper host.

6.2.  LISP Sites with Hosts using RFC 1918 Addresses Sending to non-LISP
      Sites

   In the case where RFC 1918 addressed hosts desire to communicate with
   non-LISP hosts the LISP-NAT implementation acts much like an existing
   IPv4 NAT device.  The ITR providing the NAT service must use LISP-R
   EIDs for its global pool as well as providing all the standard NAT
   functions required today.

   The source of the packet must be translated to a LISP-R EID in a
   manner similar to Section 6, and this packet must be forwarded to the
   ITR's next hop for the destination, without LISP encapsulation.

6.3.  LISP Sites with Hosts using RFC 1918 Addresses   Communicating to
      Other LISP Sites

   LISP-NAT allows a host with a RFC 1918 address to communicate with
   LISP hosts by translating the RFC 1918 address to a LISP EID.  After
   translation, the communication between source and destination ITR and
   ETRs continues as described in [LISP].

   An example of this translation and encapsulation follows.  For this
   example, a host has been assigned a RFC 1918 address of 192.168.1.2.
   In order to utilize LISP-NAT, the site has also been provided the
   LISP-R EID of 128.200.1.0/24, and uses the first address
   (128.200.1.1) as the site's RLOC.  The rest of this PA space
   (128.200.1.2 to 128.200.1.254) is used as a translation pool for this
   site's hosts who need to communicate with both non-LISP and LISP
   hosts.

   The Host 192.168.1.2 sends a packet destined for a non-LISP site to
   its default route (the ITR).  The ITR receives the packet, and
   determines that the destination is a LISP site.  How the ITR makes
   this determination is up to the ITRs implementation of the EID/RLOC
   mapping system. (reference LISP-ALT for this behavior)

   The ITR then rewrites the source address of the packet from
   192.168.1.2 to 128.200.1.2, which is the first available address in
   the LISP EID space available to it.  The ITR keeps this translation
   in a table in order to reverse this process when receiving packets
   destined to 128.200.1.2.




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   The ITR then LISP encapsulates this packet (see [LISP] for details).
   The ITR uses the site's RLOC as the LISP outer header's source, and
   the translation address as the LISP inner header's source.  Once it
   decapsulates returning traffic, it uses the entry in its LISP-NAT
   table to translate the returning packet's destination IP address and
   then forward to the proper host.

6.4.  LISP-NAT and multiple EIDs

   When a site has two address that a host might use for global
   reachability, care must be chosen on which EID is found in DNS.  For
   example, whether applications such as DNS use the LISP-R EID or the
   LISP-NR EID.  This problem exists for NAT in general, but the
   specific issue described above is unique to LISP.  Using PTRs can
   mitigate this problem, since the LISP-NR EID can be reached in all
   cases.


7.  Security Considerations

   Like any LISP ITR, PTRs will have the ability to inspect traffic at
   the time that they encapsulate.  More work needs to be done to see if
   this ability can be exploited by the control plane along the lines of
   Remote Triggered BGP Black Holes.  XXX:Reference?

   As with traditional NAT, LISP-NAT will hide the actual host ID behind
   the RLOCs used as the NAT pool.


8.  Acknowledgments

   The authors would like to acknowledge Vince Fuller for his
   contributions and review of this draft.  In addition, thanks goes to
   Christian Vogt and Lixia Zhang who have made insightful comments with
   respect to interworking and transition mechanisms.

   A special thanks goes to Scott Brim for his initial brainstorming of
   these ideas and also for his careful review.


9.  IANA Considersations

   This document creates no new requirements on IANA namespaces
   [RFC2434].


10.  References




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10.1.  Normative References

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

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

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

10.2.  Informative References

   [CRIO]     Zhang, X., Francis, P., Wang, J., and K. Yoshida, "CRIO:
              Scaling IP Routing with the Core Router-Integrated
              Overlay".

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

   [RFC2993]  Hain, T., "Architectural Implications of NAT", RFC 2993,
              November 2000.


Authors' Addresses

   Darrel Lewis
   Cisco Systems, Inc.

   Email: darlewis@cisco.com


   David Meyer
   Cisco Systems, Inc.

   Email: dmm@cisco.com






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   Dino Farinacci
   Cisco Systems, Inc.

   Email: dino@cisco.com















































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