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Versions: (draft-lewis-lisp-interworking) 00 01 02 03 04 05 06 RFC 6832

Network Working Group                                           D. Lewis
Internet-Draft                                                  D. Meyer
Intended status: Experimental                               D. Farinacci
Expires: November 27, 2009                                     V. Fuller
                                                     Cisco Systems, Inc.
                                                            May 26, 2009


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

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   This Internet-Draft will expire on November 27, 2009.

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   This document describes techniques for allowing sites running the



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   Locator/ID Separation Protocol (LISP [LISP]) to interoperate with
   Internet sites not running LISP.  A fundamental property of LISP-
   speaking sites is that they use Endpoint Identifiers (EIDs), rather
   than traditional IP addresses, in the source and destination fields
   of all traffic they emit or receive.  While EIDs are syntactically
   identical to IP addresses, routes for them are not carried in the
   global routing system so an interoperability mechanism is needed for
   non-LISP-speaking sites to exchange traffic with LISP-speaking sites.
   This document introduces two such mechanisms: the first uses a new
   network element, the LISP Proxy Tunnel Router (PTR) (Section 5) to
   act as a intermediate LISP Ingress Tunnel Router (ITR) for non-LISP-
   speaking hosts while the second adds Network Address Translation
   (NAT) functionality to LISP Ingress and LISP Egress Tunnel Routers
   (xTRs) to substitute routable IP addresses for non-routable EIDs.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  LISP Interworking Models . . . . . . . . . . . . . . . . . . .  3
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  5
   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  . . . . . . . . . .  7
   5.  Proxy Tunnel Routers . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  PTR EID announcements  . . . . . . . . . . . . . . . . . .  7
     5.2.  Packet Flow with PTRs  . . . . . . . . . . . . . . . . . .  8
     5.3.  Scaling PTRs . . . . . . . . . . . . . . . . . . . . . . .  9
     5.4.  Impact of the PTRs placement in the network  . . . . . . .  9
     5.5.  Benefit to Networks Deploying PTRs . . . . . . . . . . . .  9
   6.  LISP-NAT . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     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
     6.5.  LISP-NAT and PTRs Together . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     10.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14




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1.  Introduction

   This document describes two mechanisms for interoperation between
   LISP [LISP] sites, which use non-globally-routed EIDs, and non-LISP
   sites: use of PTRs, which create highly-aggregated routes to EID
   prefixes for non-LISP sites to follow; and the use of NAT by LISP
   ETRs when communicating with non-LISP hosts.

   A key behavior of the separation of Locators and End-Point-IDs is
   that EID prefixes are not advertised to the Internet's Default Free
   Zone (DFZ).  Specifically, only RLOCs are carried in the Internet's
   DFZ.  Existing Internet sites (and their 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 that can be used to provide reachability between sites
   that are LISP-capable and those that are not.  This document
   introduces two such mechanisms: the first uses a new network element,
   the LISP Proxy Tunnel Router (PTR) (Section 5) to act as a
   intermediate LISP Ingress Tunnel Router (ITR) for non-LISP-speaking
   hosts while the second adds a form of Network Address Translation
   (NAT) functionality to Tunnel Routers (xTRs) to substitute routable
   IP addresses for non-routable EIDs.

   More detailed descriptions of these mechanisms and the network
   elements involved may be found in the following sections:

   - Section 2 describes the different cases where interworking
   mechanisms are needed

   - Section 3 defines terms used throughout the document

   - Section 4 describes the relationship between the new EID prefix
   space and the IP address space used by the current Internet

   - Section 5 introduces and describes the operation of PTRs

   - Section 6 defines how NAT is used by ETRs to translate non-routable
   EIDs into routable IP addresses.

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


2.  LISP Interworking Models

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



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   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

   Note that while Cases 3 and 4 seem similar, there are subtle
   differences due to the way communications are originated.

   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 because
   there are no new protocol requirements placed on intermediate non-
   LISP routers.

   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.  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.

   Case 4, the most challenging, occurs when a host at a non-LISP site
   wishes to send traffic to a host at a LISP site.  If the source host
   uses a (non-globally-routable) EID as the destination IP address, the
   packet is forwarded inside the source site until it reaches a router
   which cannot forward it, at which point the traffic is dropped.  For
   traffic not to be dropped, either some route must be exist for the
   destination EID outside of LISP-speaking part of the network or an
   alternate mechanism must be in place.  Section 5 (PTRs) and Section 6
   (LISP-NAT) describe two such mechanisms.

   Note that case 4 includes packets returning to the LISP Site in case
   3.






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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.

   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 whose addresses are used as
      both globally routable IP addresses and LISP EIDs.

   LISP Non-Routable (LISP-NR) Site:  A LISP site whose 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 as a gateway between the Legacy Internet
      and the LISP enabled Network.  A given PTR advertises one or more



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      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.


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
   routing system, effectively treating them as "Provider Independent
   (PI)" prefixes.  Doing this is undesirable as it defeats one of the
   primary goals of LISP - to reduce global routing system state.

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, because these EID
   prefixes will be no 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.




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4.4.  Use of Routable EIDs for Testing LISP

   A primary design goal for LISP (and other Locator/ID separation
   proposals) is to facilitate topological aggregation of addresses and,
   thus, decrease global routing system state.  Another goal is to
   achieve the benefits of improved aggregation as soon as possible.
   Advertising routes for LISP EID prefixes into the global routing
   system is therefore not recommended.

   That being said, sites that are already using provider-aggregated
   prefixes can use these prefixes as LISP EIDs without adding state to
   the routing system; in other words, such sites do not cause
   additional prefixes to be advertised.  For such sites, connectivity
   to a non-LISP sites does not require interworking machinery because
   the "PA" EIDs are already routable.


5.  Proxy Tunnel Routers

   Proxy Tunnel Routers (PTRs) allow for non-LISP sites to communicate
   with LISP-NR sites.  A PTR is a new network element that shares many
   characteristics with the LISP ITR.  PTRs allow non-LISP sites to send
   packets to LISP-NR sites without any changes to protocols or
   equipment at the non-LISP site.  PTRs have two primary functions:

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

   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 key part of PTR functionality is to advertise routes for highly-
   aggregated EID prefixes into part of the global routing system.
   Aggressive aggregation is performed to minimize the number of new
   announced routes.  In addition, careful placement of PTRs can greatly
   reduce the scope of these new routes.  To this end, PTRs should be
   deployed close to non-LISP-speaking rather than close to LISP sites.
   Such deployment not only limits the scope of EID-prefix route
   advertisements, it also also allows traffic forwarding load to be
   spread among many PTRs.







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5.2.  Packet Flow with PTRs

   Packets from a non-LISP site can reach a LISP-NR site with the aid of
   a PTR.  By advertising a route for a particular EID prefix into the
   global routing system, traffic destined for that EID prefix is routed
   to the PTR, which then performs LISP encapsulation.  Once
   encapsulated, traffic packets use the LISP (outer) header's
   destination address to reach the destination ETR.

   What follows 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
   240.0.0.0/24.  For the purposes of this example, this prefix and no
   covering aggregate is present in the global routing system.  In other
   words, if a packet with this destination were to reach a router in
   the "Default Free Zone", it would be dropped.

   A full protocol exchange example follows:

   1.  Source host makes a DNS lookup EID for destination, and gets
       240.1.1.1 in return.

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

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

   4.  The PE has route to 240.0.0.0/24 and the next hop is the PTR.

   5.  The PTR has or acquires a mapping for 240.1.1.1 and LISP
       encapsulates, the packet now has a destination address of the
       RLOC.  The source address of this encapsulated packet is the
       PTR's RLOC.

   6.  The 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
       240.1.1.1 host in the destination LISP site.

   8.  Packets from host 240.1.1.1 will flow back through the LISP
       site's ITR.  Such packets are not encapsulated because the ITR
       knows that the destination (the original source) is a non-LISP
       site.  The ITR knows this because it can check the LISP mapping
       database for the destination EID, and on a failure determine that
       the destination site is not LISP enabled.





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   9.  Packets are then routed natively and directly to the destination
       (original source) site.

   Note that in this example the return path is asymmetric, 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).

   The asymmetric nature of traffic flows allows the PTR to be
   relatively simple - it will only have to encapsulate LISP packets.

5.3.  Scaling PTRs

   PTRs attract traffic by announcing the LISP EID namespace into parts
   of the non-LISP-speaking global routing system.  There are several
   ways that a network could control how traffic reaches a particular
   PTR to prevent it from receiving more traffic than it can handle:

      First, the PTR's aggregate routes might be selectively announced,
      giving a coarse way to control the quantity of traffic attracted
      by that PTR.

      Second, the same address might be announced by multiple PTRs in
      order to share the traffic using IP Anycast.  The asymmetric
      nature of traffic flows allows 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 approaches that a network could take in placing
   PTRs.  Placing the PTR near the ingress of traffic allows for the
   communication between the non-LISP site and the LISP site to have the
   least "stretch" (i.e. the least number of forwarding hops when
   compared to an optimal path between the sites).

   Some proposals, 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 if the EID
   prefix route advertisement points are changed (such a change might
   occur if a site adds, removes, or replaces one or more ISPs
   connections).

5.5.  Benefit to Networks Deploying PTRs

   When traffic destined for LISP-NR site arrives and is encapsulated at
   a PTR, a new LISP packet header is pre-pended.  This causes the
   packet's destination to be set to the destination site RLOC.  Because



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   traffic is thus routed towards RLOCs, it can potentially better
   follow the network's traffic engineering policies (such as closest
   exit routing).  This also means that providers who are not default-
   free and do not deploy PTRs end up sending more traffic to expensive
   transit links rather than to RLOC addresses, to which they may have
   settlement-free peering.  For large transit providers, deploying PTRs
   may attract more traffic, and therefore more revenue, from their
   customers.


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 site
   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
   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



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   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
   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



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   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 also has been provided the
   LISP-R EID of 192.0.2.0/24, and uses the first address (192.0.2.1) as
   the site's RLOC.  The rest of this PA space (192.0.2.2 to
   192.0.2.254) 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.

   The ITR then rewrites the source address of the packet from
   192.168.1.2 to 192.0.2.2, 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 192.0.2.2.

   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 addresses 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.

6.5.  LISP-NAT and PTRs Together

   With LISP-NAT, there are two EIDs possible for a given host, the
   LISP-R EID and the LISP-NR EID.  When a site has two addresses that a
   host might use for global reachability, name-to-address directories
   may need to be modified.

   This problem, global addressability, exists for NAT in general, but



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   the specific issue described above is unique to LOC/ID split schemes.
   Some schemes [ref: 6-1 proxy] have suggested running a separate DNS
   instance for legacy types of EIDs.  This solves the problem but
   introduces complexity for the site.  Alternatively, using PTRs can
   mitigate this problem, because the LISP-NR EID can hbe reached in all
   cases.

   In summary, there are two options for interworking LISP with IPv4 and
   V6.  In the NAT case the LISP site can use NAT and manage the
   transition on its own.  In the PTR case, we add a new network element
   called a PTR that can relieve that burden on the site, with the
   downside of potentially adding stretch to sites trying to reach the
   LISP site.


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.

   When LISP Sites reply to non-LISP sites and rely on PTRs to enable
   Interworking, packets will be sourced from addresses not recognized
   by their Internet Service Provider's Unicast Reverse Path Forwarding
   (uRPF) enabled on the Provider Edge Router.  Several options are
   available to the service provider.  For example they could enable a
   less strict version of uRPF, where they only look for the existence
   of the the EID prefix in the routing table.  Another, more secure,
   option is to add a static route for the customer on the PE router,
   but not redistribute this route into the provider's routing table.


8.  Acknowledgments

   Thanks goes to Christian Vogt, Lixia Zhang and Robin Whittle 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.







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9.  IANA Considerations

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


10.  References

10.1.  Normative References

   [LISP]     Farinacci, D., Fuller, V., Oran, D., and D. Meyer,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-00 (work in progress), May 2009.

   [LISP-ALT]
              Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative
              Topology (LISP-ALT)", draft-ietf-lisp-alt-00 (work in
              progress), May 2009.

   [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




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   David Meyer
   Cisco Systems, Inc.

   Email: dmm@cisco.com


   Dino Farinacci
   Cisco Systems, Inc.

   Email: dino@cisco.com


   Vince Fuller
   Cisco Systems, Inc.

   Email: vaf@cisco.com



































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