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Versions: 00                                                            
MEXT Working Group                                           R. Wakikawa
Internet-Draft                                                Toyota ITC
Intended status: Informational                              July 8, 2008
Expires: January 9, 2009

            The Design Consideration of Correspondent Router

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   Copyright (C) The IETF Trust (2008).

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Internet-Draft         Design Consideration of CR              July 2008


   This document describes the protocol design consideration of the
   correspondent router for the NEMO Basic Support Protocol.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Design Consideration . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Triggering Route Optimization  . . . . . . . . . . . . . .  4
     2.2.  Discoverying Correspondent Router  . . . . . . . . . . . .  4
     2.3.  Registering Binding to Correspondent Router  . . . . . . .  5
     2.4.  Routing Packets via Correspondent Router . . . . . . . . .  6

   3.  IANA considerations  . . . . . . . . . . . . . . . . . . . . .  9

   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10

   Appendix A.  References  . . . . . . . . . . . . . . . . . . . . . 10
     A.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     A.2.  Informative References . . . . . . . . . . . . . . . . . . 10

   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12

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1.  Introduction

   The MEXT Working Group have discussed the possible route optimization
   solution for the NEMO Basic Support protocol.  The requirements
   documents are available in IETF [ID-AUTOREQ] [ID-AEROREQ].  One of
   solution candidate is the Correspondent Router that is defined as "A
   router that is capable of terminating a Route Optimization session on
   behalf of a Correspondent Node" in [RFC-4885].  Figure 1 shows the
   overview of the route optimization for the NEMO Basic Support
   protocol by Correspondent Router.  It is the same figure of RFC-4889
   [RFC-4889].  If the Correspondent Router locates on the path between
   end-nodes, the path can be optimized compared to the dog-leg route
   (via Home Agent).

                  ************************** HAofMR
                *                            #*#
              *                            #*#   +---------------------+
            CN                           #*#     |       LEGEND        |
              o                        #*#       +---------------------+
               o   ###############   #*#         | #: Tunnel           |
                CR ooooooooooooooo MR            | *: NEMO Basic route |
                   ###############  |            | o: Optimized route  |
                                   MNN           +---------------------+

                      Figure 1: Correspondent Router

   However, the protocol design of the correspondent router is not such
   easier and simpler.  We had published "Optimized Route Cache Protocol
   (ORC)" [PAPER-ORC] [ID-ORC] as a protocol of Correspondent Router,
   but we found there are both technical and operational issues.  In
   this document, we summarize the issues and required considerations of
   the Correspondent Router.

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC-2119].

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2.  Design Consideration

   There are several issues to design a protocol for Correspondent

2.1.  Triggering Route Optimization

   In the NEMO Basic Support protocol [RFC-3963], a mobile router takes
   care of all the mobility signaling.  The mobile router first needs to
   detect the flow in or out the mobile network to initiate the route
   optimization.  The detection can be done by receiving packets of
   mobile network nodes at either ingress or egress interfaces.  In
   Mobile IPv6, the mobile host can decide whether the route
   optimization is initiated or not.  However, It is hard for the mobile
   router to optimize only specific flows.  The mobile router is an
   intermediate node between end nodes and cannot judge the route
   optimization per flow without some policy.

   The information of the policy might be a flow classification (5
   tuples), a route optimization capability (BOOLEAN: ON/OFF), etc.  The
   packets snoofing does not help much to distinguish the flow
   characteristics such as short/long-term, delay-sensitive, etc.  It is
   also hard to distinguish a flow if there are the ESP protected flows.
   There are several ways to set such policy to the mobile router.  If a
   mobile network node dynamically installs such policy to a mobile
   router, we need a new policy exchange protocol between a mobile
   network node and the mobile router.  Alternatively, the operator of
   the mobile router can statically set the policy.

   The home agent distribution such as the global HAHA [ID-HAHAINTEROP]
   [ID-HAHA] is much simpler.  The mobile router or the mobile node are
   not involving the route optimization trigger.  The trigger is given
   by the home agent.

2.2.  Discoverying Correspondent Router

   Since a correspondent router is also intermediate node on the path
   between end-nodes, it is harder to discover the address of the
   correspondent router.  We have to consider two different scenarios
   for the discovery.

   1.  Correspondent Router is located on the path of end-nodes

   2.  Correspondent Router is NOT located on the path of end-nodes

   If a correspondent router is located on the path, the mobile router
   might send control packets (ICMP, etc) and discovers the
   Correspondent Router.  This is dynamic discovery based on routing

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   mechanism.  On the other hand, if a Correspondent Router is NOT
   located on the path of end nodes, it can be discovered by some lookup
   system such as DNS.  A mobile router lookup DNS server for the
   correspondent router address of the target flow.  The anycast address
   can be also used to find the best correspondent router [ID-ORC], but
   the anycast address must be defined at any networks where
   correspondent nodes locate.  How to look up the anycast address is
   another issue.

   The global HAHA [ID-HAHAINTEROP] [ID-HAHA] does not require the
   dynamic discovering any entity, because the home agents are operated
   by the same operator and are controlled in their network.

2.3.  Registering Binding to Correspondent Router

   The Correspondent Router and the mobile router are not belong to the
   same administrative domain, there are several security concerns.
   After detecting the correspondent Router, a mobile router needs to
   send a secured binding update to the correspondent router.  However,
   since both a mobile router and a Correspondent Router are
   intermediate nodes of the end-nodes, a mechanism to secure the
   signaling between two routers is required.  The establishment cost of
   the security association might be negligible.

   Next concern is whether a mobile router sends a binding update for
   either an address of the mobile network node or prefix(es) of the
   mobile router.  If the binding is for the mobile network prefix(es),
   careful operations must be taken.  Otherwise, all the flows initiated
   from the the mobile network prefix(es) are going to be optimized with
   the correspondent router.  This might be unexpected behavior in some
   scenarios.  After the mobile router registers the prefix binding to
   the correspondent router, it is uncontrollable to optimize only
   specific flow destined to correspondent nodes behind the
   correspondent router.

   Another security concern is the address/prefix ownership verification
   of the binding.  Since the mobile router does not configure with the
   address, how can the correspondent router believe the the address in
   the binding update which is not sent from the address owner (mobile
   network node).  The prefix ownership verification is more challenging
   issue.  An address/prefix ownership verification mechanism between a
   mobile router and a correspondent router is required.  Note that the
   reachability test like Return Routability cannot be used because the
   mobile router cannot respond to the correspondent router with the
   address of the mobile network node or the mobile network prefix(es).

   In the global HAHA, all the home agents are belong to the same
   administrative group.  Therefore, we might expect the secured link

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   between home agents or might utilize strong security mechanism for
   signaling between home agents.  The prefix or address verification is
   easily operated, since the home agent delegates that address and
   prefix(es) to the mobile router.

2.4.  Routing Packets via Correspondent Router

   Even after the successful binding registration to the Correspondent
   Router, the path between two nodes should be via both the mobile
   router and the Correspondent Router (HA-MR-CR-CN).  However, some
   considerations are required to keep the ideal path by the operators
   of the Mobile Router and the Correspondent Router.  The routing
   managements are another challenging issue of the Correspondent
   Router.  The issues are classified into two parts: MR-CR routing path
   management and CN-CR routing path management.

   MR-CR Route Management:

   In Figure 1, the path between a correspondent node and a mobile
   network node is drawn as the symmetric path.  However, in the current
   Internet, the path is often asymmetric.  Many autonomous systems has
   multiple peering points and injects the own routes from them.
   Therefore, even if one direction is optimized, there is no guarantee
   that the reverse path is also optimized (Figure 2).  Therefore, for
   the deployment of correspondent routers, the operator must be
   carefully managed their network in terms of routing, the location of
   correspondent routers, and the number of correspondent routers, etc.
   Note that this management is relatively difficult because the mobile
   router changes its attachment point.  The path between the mobile
   router and the correspondent router is changed by the mobile router's

                + +++++++++++++++++++++++++ HAofMR
               +        --------->          #+#
              +                            #+#   +---------------------+
            CN                           #+#     |       LEGEND        |
             o                          #+#      +---------------------+
               o   ###############   #+#         | #: Tunnel           |
                CR ooooooooooooooo MR            | +: CN -> MNN        |
                   ###############  |            | o: MNN -> CN        |
                    <----------    MNN           +---------------------+

            Figure 2: Asymmetric Path (MR-CN Route Management)

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   CN-CR Route Management:

   Another routing management issue is how the Correspondent Router
   handle the packets meant for the mobile router from correspondent
   nodes.  In Figure 3, there are two exit routers toward the Internet
   in the site of correspondent node and place one or more correspondent
   routers at the exit router as an example configuration.

         MNN                   MNN                    MNN
          |                     |                     |
          MR#######HAofMR       MR#                   MR
          #          o          #  #                  #
          #          o          #    #               #
          #          o          #      #            #
         CR1      Router       CR1       CR2       CR1###### CR2
            +      o              +      o            +      o
             +    o                +    o              +    o
               CN                    CN                  CN

               a)                    b)                  c)

         Figure 3: Multiple Exit Routers (CN-CR Route Management)

   In Figure 3-a), if the packets from the correspondent node is routed
   to the Router, the packet is routed through the home agent (i.e.
   unoptimized path).  In order to optimize the path, the operator MUST
   guarantee that the Correspondent Router (CR1) receives all packets
   meant for the mobile router from correspondent nodes.  To do so, the
   CR1 dynamically injects the mobile network prefix of the mobile
   router to the site of the correspondent node.  This injecting routes
   will be available while the CR1 manages the active binding of the
   mobile router.  However, from the administrative and operational
   point of view, the route injection of the different prefixes from its
   autonomous system are often restricted.

   Another approach is shown in Figure 3-b) and -c).  Correspondent
   Routers are placed at all the exit routers of the site.  We now
   investigate the multiple correspondent router managements.  This
   configuration might brings other routing management issues inside the
   site of the correspondent router.

   In Figure 3-b), the mobile router sends a binding update to both CR1
   and CR2 to establish bi-directional tunnels.  It causes additional
   overheads to the mobile router such as 1) discovering all the
   correspondent routers, 2) sending multiple binding updates, 3)
   managing multiple tunnels.

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   Alternatively, after receiving a binding update from the mobile
   router, the receiver of the binding update (let's say CR1 as an
   example) synchronizes the state with the other correspondent routers
   (CR2) in Figure 3-c).  The CR2 establishes a tunnel to the CR1 for
   the packets destined to the mobile network prefix.  Additional
   protocols such as inter-correspondent router protocol like the inter-
   HAHA protocol [ID-HAHA] might be required.

   In the global HAHA, the differences might be 1) the aggregated route
   injection per the home prefix (sets of the mobile network prefixes),
   2) the stable (controlled?!) route injection (no dynamic injection).
   Each home agent in the global HAHA injects its entire home prefix
   from different location and advertise that the aggregated home prefix
   route persistently.  The routing management of the HAHA must be more
   controllable for operators than the one of Correspondent routers.

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3.  IANA considerations

   This document does not require any IANA action.

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4.  Security Considerations

   Security vulnerability is not introduced in this specification.

Appendix A.  References

A.1.  Normative References

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

   [RFC-3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
   Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
   January 2005.

A.2.  Informative References

   [RFC-3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
   RFC 3753, June 2004.

   [RFC-4885] Ernst, T. and H. Lach, "Network Mobility Support
   Terminology", RFC 4885, July 2007.

   [RFC-4888] C. Ng, et. al, "Network Mobility Route Optimization
   Problem Statement", RFC 4888, July 2007.

   [RFC-4889] C. Ng, et. al, "Network Mobility Route Optimization
   Solution Space Analysis", RFC 4889, July 2007.

   [ID-HAHA] Thubert, P., Wakikawa, R., and V. Devarapalli, "Global HA
   to HA protocol", Work in Progress, September 2006.

   [ID-HAHAINTEROP] R. Wakikawa, K. Shima and N. Shigechika, "The Global
   HAHA Operation at the Interop Tokyo 2008",
   draft-wakikawa-mext-haha-interop2008-00.txt (work in progress), July

   [ID-AEROREQ] W. Eddy, et. al,"NEMO Route Optimization Requirements
   for Operational Use in Aeronautics and Space Exploration Mobile
   Networks", draft-ietf-mext-aero-reqs-02.txt, May 2008.

   [ID-AUTOREQ] R. Baldessari, et. al, "Automotive Industry Requirements
   for NEMO Route Optimization",
   draft-ietf-mext-nemo-ro-automotive-req-00.txt, February 2008.

   [PAPER-ORC] Wakikawa, R., Koshiba, S., Uehara, K., and J. Murai,

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   "ORC: Optimized Route Cache Management Protocol for Network
   Mobility", 10th International Conference on Telecommunications, vol
   2, pp 1194-1200, February 2003.

   [ID-ORC] Wakikawa, R. and M. Watari, "Optimized Route Cache Protocol
   (ORC)", Work in Progress, November 2004.

Author's Address

   Ryuji Wakikawa
   Toyota ITC / Keio University
   6-6-20 Akasaka, Minato-ku
   Tokyo  107-0052

   Phone: +81-3-5561-8276
   Fax:   +81-3-5561-8292
   Email: ryuji@jp.toyota-itc.com

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