Network Working Group P. Thubert Internet-Draft M. Molteni Expires: December 2, 2003 Cisco Systems C. Ng Panasonic Singapore Labs June 3, 2003 Taxonomy of Route Optimization models in the Nemo Context draft-thubert-nemo-ro-taxonomy-01 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 2, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract Nemo enables Mobile Networks by extending Mobile IP to support Mobile Routers. This paper documents how the MIPv6 concept of Route Optimization can to be adapted for Nemo to optimize: 1. the nested tunnels of the nested Nemo configuration 2. router-to-router in the infrastructure as opposed to end-to-end. and much more ... :) Thubert, et al. Expires December 2, 2003 [Page 1] Internet-Draft RO-Taxonomy June 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3 2. Nested Mobile Network . . . . . . . . . . . . . . . . . . 3 2.1 Nested Tunnels Optimization . . . . . . . . . . . . . . . 3 2.1.1 Pitfalls and threats . . . . . . . . . . . . . . . . . . . 7 2.1.1.1 Securing the protocol . . . . . . . . . . . . . . . . . . 7 2.1.1.2 Recursive complexity . . . . . . . . . . . . . . . . . . . 7 2.2 Route Optimization inside the Nested Mobile Network . . . 8 3. MR-to-CN . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. MIPv6 Route Optimization over Nemo . . . . . . . . . . . . 9 5. Optimization within the infrastructure . . . . . . . . . . 9 5.1 Route Optimization within a ISP network . . . . . . . . . 10 5.2 Correspondent Router . . . . . . . . . . . . . . . . . . . 11 5.3 Distributed Anchor Routers . . . . . . . . . . . . . . . . 12 6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 13 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 13 References . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 15 Full Copyright Statement . . . . . . . . . . . . . . . . . 16 Thubert, et al. Expires December 2, 2003 [Page 2] Internet-Draft RO-Taxonomy June 2003 1. Introduction This document assumes the reader is familiar with Mobile IPv6 defined in [1], with the concept of Mobile Router (MR) and with the Nemo terminology defined in [2]. From the discussions on the mailing list, it appears that the common current understanding of the problem space of Route Optimization (RO), in the Nemo context, is still limited. This paper attempts to clarify the state of the discussion and propose a taxonomy of the various aspects of the problem. We will look at different possible types of route optimizations related to mobile network. Firstly, route optimizations involving nested mobile networks are explored. This involves minimizing the number of tunnels required when there is multiple levels of nesting. Secondly, the Mobile Router can initiate route optimization with corresponding nodes (CN) on behalf of the mobile network nodes (MNN). Thirdly, we consider the feasibility of having a visiting mobile node (VMN) performing MIPv6 RO over the NEMO base protocol. Lastly, we explore the prospect of performing RO over the routing infrastructure. This involve optimizing the route between two routers situated near to each end point. 2. Nested Mobile Network 2.1 Nested Tunnels Optimization Let us illustrate the problem by an example. In this example, the nested Mobile Network has a tree topology. In the tree each node is a basic Mobile Network, represented by its MR. Thubert, et al. Expires December 2, 2003 [Page 3] Internet-Draft RO-Taxonomy June 2003 +---------------------+ | Internet |---CN +---------------|-----+ / Access Router MR3_HA | ======?====== MR1 | ====?=============?==============?=== MR5 MR2 MR6 | | | =========== ===?========= ============= MR3 | ==|=========?== Net3 LFN1 MR4 | ========= An example nested Mobile Network This example focuses on a Local Fixed Node (LFN) at depth 3 (in Net3) inside the tree, represented by its mobile router MR3. The path to the Top Level Mobile Router (TLMR) MR1 and then the Internet is: MR3 -> MR2 -> MR1 -> Internet Consider the case where a LFN belonging to Net3 sends a packet to a Correspondent Node (CN) in the Internet, and the CN replies back. With no Nested Tunnels Optimization, we would have three bi- directional nested tunnels, as described in [3] and illustrated in the following drawings: -----------. --------/ /-----------. -------/ | | /----------- CN ------( - - | - - - | - - - | - - - | - - - (-------- LFN MR3_HA -------\ | | \----------- MR3 MR2_HA --------\ \----------- MR2 MR1_HA ----------- MR1 No Nested Tunnels Optimization Thubert, et al. Expires December 2, 2003 [Page 4] Internet-Draft RO-Taxonomy June 2003 Such a solution introduces the following problems: "Pinball" routing Both inbound and outbound packets will flow via the HAs of all the MRs on their path within the NEMO, with increased latency, less resilience and more bandwidth usage. To illustrate this effect, the figure below shows the route taken by a packet sent from LFN to CN: +--> HAofMR1 ---------------------+ | | +----------------- HAofMR2 <--+ | | | +---------------+ | | V HAofMR3 <------+ CN | | LFN --> MR1 --> MR2 --> MR3 'Pinball' Routing Packet size An extra IPv6 header is added per level of nesting to all the packets. The header compression suggested in [4] cannot be applied because both the source and destination (the intermediate MR and its HA), are different hop to hop. On the other hand, with a Nested Tunnel Optimization, we would have at most one bi-directional tunnel outside the Mobile Network, that may depend on the traffic flow: __- --_ Tunnel---------------------------- MR1 ( Mobile ) MR3 CN ----------( - - - - - - - - - - ( - - - - )--------- LFN Endpoint---------------------------- MR1 ( Network ) MR3 --___--- Nested Tunnels Optimization The end-point of such a Tunnel on the Mobile side may either be MR1 or MR3, depending on the solution. In the case of a Mobile Node visiting Net3, that Mobile Node may also be the end-point. Thubert, et al. Expires December 2, 2003 [Page 5] Internet-Draft RO-Taxonomy June 2003 The potential approaches for avoiding the nesting of tunnels include: Mobile Aggregation This model applies to a category of problems were the Mobile Networks share a same administration and consistently move together (e.g. a fleet at sea). In this model, there is a cascade of Home Agents. The main Home Agent is fixed in the infrastructure, and advertises an aggregated view of all the Mobile Networks. This aggregation is actually divided over a number of Mobile Routers, the TLMRs. The TLMRs subdivide some of their address space to the other Mobile Routers forming their fleet, for which they are Home Agent. As Home Agents, the TLMRs terminate MIP Tunnels from the inside of the Mobile Network. As Mobile Router, they also terminate their home Tunnels. As routers, they forward packets between the 2 tunnels. Surrogate The TLMR acts as a proxy in the MIP registration, in a fashion of MIPv4 Foreign Agent or HMIP MAP (see [8]). For instance, the TLMR maintains a Tunnel to each MR, a Tunnel to the HA of each MR, and switches packets between the two. Internal Routing and gateway This item can be approached from a MANET standpoint. This was already done for DSR (see [9]) and AODV (see [10] and [7]) From a Nemo standpoint, a full MANET is not necessary since the goal is to find a way to the infrastructure, as opposed to any-to-any connectivity. RRH The Reverse Routing Header (RRH) approach avoids the multiple encapsulation of the traffic but maintains the home tunnel of the first MR on the egress path. It is described in details in [5]. The first MR on the way out (egress direction) encapsulates the packet over its reverse tunnel, using a form of Record Route header, the RRH. The next MRs simply swap their CoA and the source of the packet, saving the original source in the RRH. The HA transforms the RRH in a Routing Header to perform a Source Routing across the nested Mobile Network, along the ingress path to the target MR. Thubert, et al. Expires December 2, 2003 [Page 6] Internet-Draft RO-Taxonomy June 2003 Access Router Option The Access Router Option (ARO) approach [6] is somewhat similar to the RRH in that only the home tunnel of the first MR in the egress path is maintained. This is done by having MR to send an ARO in Binding Update to inform its HA the address of its access router. Using this information, HA can build a Routing Header to source- route a packet to the target MR within in a nested mobile network. Details can be found in [6]. 2.1.1 Pitfalls and threats 2.1.1.1 Securing the protocol These approaches are generally difficult to secure unless all the Mobile Routers and Visiting Mobile Node belong to a same administrative domain and share predefined Security Associations. Even if an intermediate MR is 'trusted', this does not prove it is able to provide the necessary bandwidth, and may not provide a good service. Eventually, a MR that is capable of securing (IPSec) its traffic may select a Mobile Access Router based on quality of service heuristics as opposed as trust. The problem is global to the whole Mobile Network in the case of a MANET-based solution. For an RRH-based solution, the threat comes from on-axis MRs in the nested Mobile Network but is mostly limited to denial of service. This is detailed in [5]. The approach taken is to limit the threat to Black Hole and Grey Hole by using IPSec. 2.1.1.2 Recursive complexity A number of drafts and publications suggest -or can be extended to- a model where the Home Agent and any arbitrary Correspondent would actually get individual binding from the chain of nested Mobile Routers, and form a routing header appropriately. An intermediate MR would keep track of all the pending communications between hosts in its subtree of Mobile Networks and their CNs, and a binding message to each CN each time it changes its point of attachment. If this was done, then each CN, by receiving all the binding messages and processing them recursively, could infer a partial topology of the nested Mobile Network, sufficient to build a multi-hop routing header for packets sent to nodes inside the nested Mobile Network. Thubert, et al. Expires December 2, 2003 [Page 7] Internet-Draft RO-Taxonomy June 2003 However, this extension has a cost: 1. Binding Update storm when one MR changes its point of attachment, it needs to send a BU to all the CNs of each node behind him. When the Mobile Network is nested, the number of nodes and relative CNs can be huge, leading to congestions and drops. 2. Protocol Hacks Also, in order to send the BUs, the MR has to keep track of all the traffic it forwards to maintain his list of CNs. In case of IPSec tunneled traffic, that CN information may not be available. 3. CN operation The computation burden of the CN becomes heavy, because it has to analyze each BU in a recursive fashion in order to infer nested Mobile Network topology required to build a multi hop routing header. 4. Missing BU If a CN doesn't receive the full set of PSBU sent by the MR, it will not be able to infer the full path to a node inside the nested Mobile Network. The RH will be incomplete and the packet may or may not be delivered. 5. Obsolete BU If the Binding messages are sent asynchronously by each MR, then, when the relative position of MRs and/or the TLMR point of attachment change rapidly, the image of Mobile Network that the CN maintains is highly unstable. If only one BU in the chain is obsolete due to the movement of an intermediate MR, the connectivity may be lost. 2.2 Route Optimization inside the Nested Mobile Network This is not part of the Nemo Charter. The expectation is that the mobile routes installed by Nemo can cohabit with a MANET support that would perform the RO inside the Nested Mobile Network. In other words, MIP redistributes its prefixes locally to a MANET and the MR-HA tunnel is bypassed. Thubert, et al. Expires December 2, 2003 [Page 8] Internet-Draft RO-Taxonomy June 2003 3. MR-to-CN This section covers the case where the Route Optimization is performed between the MR and the Correspondent Node. A major issue is that the MIPv6 Reverse Routability test is broken, since it is meant to ensure that the CoA (the MR) an the Home Address (the Mobile Node) are collocated. With a Mobile Network, a LFN is reachable via the Care-Of Address, but not at the Care-Of Address. Some tricks may be performed on the fly by the MRs but it seems that a clean MR-to-CN optimization for Nemo will impact the CN function. Once we modify the CN behavior, we need to introduce a negotiation from the start of the RR test to determine the protocol. In particular, the Mobile Node and the CN must decide whether checking the collocation is possible, and if not, whether a CN is willing to accept the risk. If not, the optimization may be limited to triangular routing MR->CN->HA->MR. This is a major evolution from [1], since MIPv6 has no such negotiation capability at this time. 4. MIPv6 Route Optimization over Nemo When a Mobile Node visits a Mobile Network, the best Route Optimization is obtained if the path in the Infrastructure is the same as if the Mobile Network was attached at the attachment point of the Mobile Router (i.e., there is not additional Tunneling that is linked to Nemo). A possible approach to this is to extend the solution for nested mobile network optimization to include VMN as well. In this case, the VMN is treated as though it is an MR. This type of solution will most likely require some extensions for a MIPv6 VMN and CN. 5. Optimization within the infrastructure This section elaborates on cases where the Route Optimization is performed within the Routing Infrastructure. In this model, both the LFN behind the MR and the Correspondent can be MIP agnostic. The drawback is the introduction of Mobile Routes in specific Routers, causing additional signaling and load to the Routing Fabric. The general idea is that there is a correspondent-side Router in the infrastructure that is located "closer" to the Correspondent than the HA. That Router can terminate MIP on behalf of the CN. Thubert, et al. Expires December 2, 2003 [Page 9] Internet-Draft RO-Taxonomy June 2003 Correspondent nnnnnnnnnnnnnnnnnnnnnnnn Home Agent # n # o # n # # :== Tunnel o # n # o :== Optimized o # n # n :== Non-Optimized o # n # ################################## n # C-Side oooooooooooooooooooooooooooooooo Mobile Router ################################ Router | ====Mobile Network======= Optimization in the Infrastructure This optimization is only valid when the path via the correspondent- side Router is shorter than the path via the Home Agent. The Optimization can take place independently for the 2 directions of the traffic: Egress The MR locates the correspondent-side Router, establishes a Tunnel with that Router and sets a route to the Correspondent via the correspondent-side Router over the Tunnel. At this point, the traffic to the Correspondent does not flow via the Home Agent anymore. Ingress The correspondent-side Router is on the way of the traffic from the Correspondent to the Home Agent. Also, it is aware of the MR and the Mobile Networks behind the MR and establishes the appropriate Tunnel and Route. At that point, it is able to reroute the traffic to the Mobile Network over the Tunnel to the MR. 5.1 Route Optimization within a ISP network This form of Route Optimization provides local savings for a ISP. This idea was described in Ohnishi's Mobile Border Gateway draft. The goal is to locate the closest (BGP) gateway for a Correspondent that is located outside of the domain, and tunnel between the MR and that gateway as opposed to the Home Agent for that specific Correspondent. Thubert, et al. Expires December 2, 2003 [Page 10] Internet-Draft RO-Taxonomy June 2003 5.2 Correspondent Router A globally better optimization is obtained if the tunnel from the MR is terminated closer to the destination on the Correspondent side. This is the role of a Correspondent Router (CR). +-------------------+ # :== Tunnel | Autonomous System | o :== Optimized | ----------------- | n :== Non-Optimized | | | | | Correspondent nnnnnnnnnnnnnnnnnnnnnnnnnnnnn Home Agent | | # n # | o | # n # | o | # n # | o | # n # | o | # n # | o | # n # | #################################### ? | CR oooooooooooooooooooooooooooooooooooooo Mobile | #################################### Router | | | +-------------------+ ===========Mobile Network======== Correspondent Router The MR locates the CR for a given Correspondent and establishes a Tunnel to the CR for that destination and its prefix(es). Then, the CR establishes the Tunnel back to the MR and the Mobile Routes to the MR's Mobile Networks via that Tunnel. A key point is that the CR must be on the interception path of the traffic from the Correspondent to the Mobile Networks in order to reroute the traffic over the appropriate Tunnel. This can be achieved in several fashions: Redistribution There's a limited Number of CRs that cover an Autonomous System. They redistribute the Mobile Routes on the fly, or within rate and amount limits. Garbage Collection is done at appropriate time to limit the perturbation on the Routing. Default Router The CR is a Default Router for the Correspondent, or for the whole AS of the Correspondent (it's a border gateway). In this case, redistribution is not needed. Thubert, et al. Expires December 2, 2003 [Page 11] Internet-Draft RO-Taxonomy June 2003 Core Routers The Core Routers for the network of the Correspondent are all CRs. If the path from the correspondent to the Home Agent does not pass via a CR, then it's not worth optimizing. If it is, then the CRs are on the way. Again, redistribution is not needed. 5.3 Distributed Anchor Routers Taking the idea of a correspondent router a step further, it is possible to have a distributed set of anchor routers across the Internet. Outgoing packets sent from a mobile network will be tunneled to one of the nearest anchor router (instead of to the home agent of the mobile router). This M-Side (Mobile Network Side) anchor router will decapsulate the packet, inspect the destination, and tunnel the packet to another anchor router situated near the CN (C-Side Anchor Router). From there, the packet will be decapsulated and forwarded to the CN. Correspondent nnnnnnnnnnnnnnnnnnnnnnn Home Agent o # n # o # n # # :== Tunnel o # n # o :== Optimized o # n # n :== Non-Optimized o # n # C-Side ################## M-Side ###### n # Anchor oooooooooooooooooo Anchor oooo Mobile Router ################## Router #### Router | ====Mobile Network======= Optimization in the Infrastructure The C-Side Anchor Router will be subjected to the same condition as listed in the previous sub-section if packets sent from the CN to the mobile network are to be route-optimized too. Otherwise, the solution will only partially optimize routing to a triangular routing (i.e. packet sent by CN will still go through the home agent of the mobile network). The anchor router share many similarities with the concept of Mobility Anchor Point (MAP) proposed in Hierarchical MIPv6 (HMIPv6) [8]. In fact, it can be combined with HMIPv6 whereby each M-Side anchor router is also an MAP, and the MR obtains a regional care-of- address from the MAP. Thubert, et al. Expires December 2, 2003 [Page 12] Internet-Draft RO-Taxonomy June 2003 6. Conclusion The Problem space of Route Optimization in the Nemo context is multifold and can be split is several work areas. It will be critical, though, that the solution to a given piece of the puzzle be compatible and integrate smoothly with the others. Hopefully, the solutions will build on MIPv6 ([1]), as recommended by the Nemo Charter. On the other hand, MIPv6 seems to be evolving in a direction that makes it more and more difficult to provide a Nemo solution with backward compatibility, since: 1) The RR test prevents a MR-LFN dichotomy on the Mobile Side, 2) The RR test has no negotiable option and is not open for extension, and 3) The HaO and RH type 2 are designed for a collocated CareOf Address. More specifically, they are not designed to be multi-hop as RRH is, and not extensible, though RRH can be considered as an extension of HaO. The authors intent is to trigger fruitful discussions that in turn will enhance our common understanding of the problem space so that at some point, this paper turns into a problem statement for the Nemo Route Optimization. 7. Acknowledgements The authors wish to thank: Greg Daley, Thierry Ernst, Hiroyuki Ohnishi, T.J. Kniveton, Alexandru Petrescu, Hesham Soliman, Ryuji Wakikawa and Patrick Wetterwald for their various contributions. Thubert, et al. Expires December 2, 2003 [Page 13] Internet-Draft RO-Taxonomy June 2003 References [1] Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in IPv6", draft-ietf-mobileip-ipv6-21 (work in progress), March 2003. [2] Lach, H. and T. Ernst, "Network Mobility Support Terminology", draft-ietf-nemo-terminology-00 (work in progress), May 2003. [3] Kniveton, T., "Mobile Router Tunneling Protocol", draft- kniveton-mobrtr-03 (work in progress), November 2002. [4] Deering, S. and B. Zill, "Redundant Address Deletion when Encapsulating IPv6 in IPv6", draft-deering-ipv6-encap-addr- deletion-00 (work in progress), November 2001. [5] Thubert, P. and M. Molteni, "IPv6 Reverse Routing Header and its application to Mobile Networks", draft-thubert-nemo- reverse-routing-header-01 (work in progress), October 2002. [6] Tanaka, T. and C. Ng, "Securing Nested Tunnels Optimization with Access Router Option", draft-ng-nemo-access-router-option- 00 (work in progress), November 2002. [7] Wakikawa, R., "Global Connectivity for IPv6 Mobile Ad Hoc Networks", draft-wakikawa-manet-globalv6-02 (work in progress), November 2002. [8] Castelluccia, C., Malki, K., Soliman, H. and L. Bellier, "Hierarchical Mobile IPv6 mobility management (HMIPv6)", draft- ietf-mobileip-hmipv6-07 (work in progress), October 2002. [9] Johnson, D., Maltz, D., Broch, J. and J. Jetcheva, "The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks", draft- ietf-manet-dsr-07 (work in progress), February 2002. [10] Das, S., Perkins, C. and E. Royer, "Ad Hoc On Demand Distance Vector (AODV) Routing", draft-ietf-manet-aodv-13 (work in progress), February 2003. [11] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [12] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. Thubert, et al. Expires December 2, 2003 [Page 14] Internet-Draft RO-Taxonomy June 2003 Authors' Addresses Pascal Thubert Cisco Systems Technology Center Village d'Entreprises Green Side 400, Avenue Roumanille Biot - Sophia Antipolis 06410 FRANCE EMail: pthubert@cisco.com Marco Molteni Cisco Systems Technology Center Village d'Entreprises Green Side 400, Avenue Roumanille Biot - Sophia Antipolis 06410 FRANCE EMail: mmolteni@cisco.com Chan-Wah Ng Panasonic Singapore Laboratories Pte Ltd Blk 1022 Tai Seng Ave #06-3530 Tai Seng Industrial Estate Singapore 534415 SG EMail: cwng@psl.com.sg Thubert, et al. Expires December 2, 2003 [Page 15] Internet-Draft RO-Taxonomy June 2003 Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Thubert, et al. Expires December 2, 2003 [Page 16]