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Thaler 3 February 25, 2006 Microsoft 4 Expires August 2006 6 Multi-Subnet MANETs 7 9 Status of this Memo 11 By submitting this Internet-Draft, each author represents that any 12 applicable patent or other IPR claims of which he or she is aware 13 have been or will be disclosed, and any of which he or she becomes 14 aware will be disclosed, in accordance with Section 6 of BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six 22 months and may be updated, replaced, or obsoleted by other documents 23 at any time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/1id-abstracts.html 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 Copyright Notice 34 Copyright (C) The Internet Society (2006). All Rights Reserved. 36 Abstract 38 This document describes an approach to addressing nodes in Mobile 39 Ad-hoc Networks (MANETs) which involves assigning a separate subnet 40 to each MANET router. This approach avoids many of the problems 41 that arise in other approaches, and is intended to allow existing 42 protocols and applications to work unmodified. 44 1. Introduction 46 A Mobile Ad-hoc Network (MANET) is one in which the topology may be 47 very dynamic, such as highly mobile nodes communicating over a 48 wireless medium. In this document we assume that there are 49 forwarding nodes which participate in a MANET routing protocol. 50 Furthermore, we assume that there may also be non-MANET nodes 51 attached behind MANET forwarding nodes (e.g., via wired Ethernet). 52 We will use the term "MANET router" to refer to the first type of 53 nodes, and "client" to refer to the latter type of nodes. 55 Draft Multi-Subnet MANETs February 2006 57 There are three general approaches to architecting the data 58 (forwarding) plane: 60 (A) Treat the entire MANET as a single link, and do all forwarding 61 at the datalink-layer, exposing (say) normal Ethernet to IP. 62 The control plane thus consists of a layer-2 routing protocol. 63 In this approach, existing protocols and applications work 64 normally. 66 (B) Treat the MANET as a single subnet composed of multiple links, 67 such that MANET routers must do layer-3 forwarding (decrement 68 TTL, etc.) between nodes in the same subnet. The control plane 69 consists of a layer-3 MANET routing protocol. This approach 70 has a number of problems as discussed in [MLSI], and may break 71 existing protocols and applications. Clients are either not 72 supported at all, or some additional proxying method is 73 required. 75 (C) Treat the MANET as a site containing many subnets, such that 76 MANET routers act as normal routers when forwarding data 77 between subnets. The control plane consists of a layer-3 MANET 78 routing protocol, as with approach (B). This approach avoids 79 most of the problems of (B), easily supports clients, and is 80 what the remainder of this document outlines. 82 2. Overview 84 The MANET is treated as a site composed of many subnets. Each MANET 85 router is assigned its own subnet prefix(es). Each client is 86 assigned its own IP address(es) on a subnet assigned to a MANET 87 router to which it is attached. 89 The MANET site may or may not have external connectivity. If there 90 is, then any site gateways are configured with the site prefix(es) 91 and advertise them into the external routing system, as normal site 92 gateways do. If there is no external connectivity, then one or more 93 MANET routers are configured with the site prefix(es), e.g., a 94 Unique Local IPv6 Prefix [RFC4193], and 10/8 for IPv4 [RFC1918]. It 95 may be possible to automatically generate a site prefix for the site 96 in a zero-configuration MANET (e.g., by electing one node to do so), 97 but such a mechanism is outside the scope of this document. Note 98 that a /48 IPv6 site prefix results in the ability to support up to 99 2^16 MANET routers, plus any clients behind them. 101 Each router then uses a subnet allocation protocol to acquire one or 102 more subnet prefixes within the site prefix. It then uses this 103 subnet prefix to number itself and any clients. 105 As a result, this approach needs only two MANET-specific protocols: 107 1) A routing protocol capable of exchanging subnet routes, and 109 2) A subnet allocation protocol capable of allocating prefixes. 111 Draft Multi-Subnet MANETs February 2006 113 All other protocols and applications operate normally. 115 3. Client Behavior 117 Clients operate with no changes, using normal IPv4 and IPv6 118 mechanisms. 120 4. MANET Router Behavior 122 4.1. Obtaining a subnet prefix 124 The requirements for a subnet allocation protocol are: 126 1) Must be capable of allocating a subnet prefix (not just a single 127 address). 129 2) Must prevent duplicate subnet prefix assignments. 131 3) Must handle network partitions and heals, due to the highly 132 dynamic nature of a MANET. 134 4) Must complete rapidly, with low overhead. 136 5) Must support a bootstrap scenario where all MANET routers without 137 a manually configured prefix attempt to allocate a prefix at the 138 same time. 140 6) Should support the ability to detect duplicate layer-2 addresses. 142 7) Should support the ability to detect a duplicate IPv6 link-local 143 address within the MANET site (since the dynamic nature means 144 that any other router may eventually be on the same link, this 145 helps avoid future conflicts). 147 Details of the actual subnet allocation protocol are outside the 148 scope of this draft. At a high level, an address allocation 149 protocol proposed for a multilink-subnet approach (approach B) can 150 be modified to be suitable, by inclusion of a prefix length. 152 4.2. Using a subnet prefix 154 One common practice in BGP is to assign a routable address to the 155 router's loopback interface, and use that for communication which 156 may be routed over different physical interfaces over time (e.g., to 157 survive failures). 159 In the same vein, a MANET router takes its allocated prefix, assigns 160 it to its loopback interface, and advertises it in the MANET routing 161 protocol. If the MANET router also has a client interface (e.g., an 162 Ethernet link with wired clients attached), then the implementation 163 can either allocate a second subnet prefix for that link, or may 164 simply assign its sole subnet prefix to a client interface rather 165 than its loopback interface. The MANET router then assigns its own 166 Draft Multi-Subnet MANETs February 2006 168 IPv4 and/or IPv6 addresses on its loopback interface by using a 169 fixed address suffix (e.g., .1 in IPv4 and ::1 in IPv6). 171 The MANET router's other interfaces (e.g., a wireless interface used 172 to communicate with other MANET routers) is not given an IPv4 173 address (i.e., left unnumbered). An IPv6 link-local address is 174 assigned per normal IPv6 stateless address autoconfiguration 175 [RFC2462]. Note that normal IPv6 Duplicate Address Detection may 176 occur as usual, but the MANET routers seen on that link will change 177 over time. DAD need not be redone as long as the subnet allocation 178 protocol is responsible for detecting duplicate IPv6 link-local 179 addresses. 181 Applications running on the MANET router will use the loopback 182 interface, since that is the one with the global address on it. All 183 other MANET nodes will appear to the application as being off- 184 subnet. 186 5. Security Considerations 188 Often the hardest attacks to defend against are on-link attacks 189 (e.g., ARP attacks in IPv4). Unlike the other two approaches, this 190 approach narrows the set of nodes which are on-link to only those 191 nodes which are nearby, as opposed to being anywhere in the MANET. 192 In addition to mitigations in various protocols, this may make 193 social mitigations easier as well. 195 In addition, since this approach does not change the standard 196 address allocation and forwarding mechanisms in IPv4 and IPv6, it 197 avoids the security issues mentioned in [MLSI], resulting in a 198 potentially more secure environment than with a multilink subnet 199 approach. 201 The routing protocol in use must be secured to avoid attackers 202 misrouting packets. The issues here are discussed in [RFC2501]. 204 The subnet allocation protocol in use must also be secured to avoid 205 attackers consuming all available subnet space, or preventing 206 legitimate MANET routers from obtaining a subnet prefix. 208 6. IANA Considerations 210 This document has no actions for IANA. 212 7. Acknowledgements 214 Suresh Krishnan first suggested assigning a subnet prefix to each 215 MANET node. 217 Draft Multi-Subnet MANETs February 2006 219 8. Normative References 221 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 222 and E. Lear, "Address Allocation for Private Internets", 223 BCP 5, RFC 1918, February 1996. 225 [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address 226 Autoconfiguration", RFC 2462, December 1998. 228 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 229 Addresses", RFC 4193, October 2005. 231 9. Informative References 233 [MLSI] Thaler, D., "Issues With Protocols Proposing Multilink 234 Subnets", draft-thaler-intarea-multilink-subnet-issues- 235 00.txt, February 2006. 237 [RFC2501] Corson, S. and J. Macker, "Mobile Ad hoc Networking 238 (MANET): Routing Protocol Performance Issues and 239 Evaluation Considerations", RFC 2501, January 1999. 241 Authors' Addresses 243 Dave Thaler 244 Microsoft 245 One Microsoft Way 246 Redmond, WA 98052 247 Phone: +1 425 703 8835 248 Email: dthaler@microsoft.com 249 Draft Multi-Subnet MANETs February 2006 251 Full Copyright Statement 253 Copyright (C) The Internet Society (2006). 255 This document is subject to the rights, licenses and restrictions 256 contained in BCP 78, and except as set forth therein, the authors 257 retain all their rights. 259 This document and the information contained herein are provided on 260 an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 261 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE 262 INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR 263 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 264 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 265 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 267 Intellectual Property 269 The IETF takes no position regarding the validity or scope of any 270 Intellectual Property Rights or other rights that might be claimed 271 to pertain to the implementation or use of the technology described 272 in this document or the extent to which any license under such 273 rights might or might not be available; nor does it represent that 274 it has made any independent effort to identify any such rights. 275 Information on the procedures with respect to rights in RFC 276 documents can be found in BCP 78 and BCP 79. 278 Copies of IPR disclosures made to the IETF Secretariat and any 279 assurances of licenses to be made available, or the result of an 280 attempt made to obtain a general license or permission for the use 281 of such proprietary rights by implementers or users of this 282 specification can be obtained from the IETF on-line IPR repository 283 at http://www.ietf.org/ipr. 285 The IETF invites any interested party to bring to its attention any 286 copyrights, patents or patent applications, or other proprietary 287 rights that may cover technology that may be required to implement 288 this standard. Please address the information to the IETF at ietf- 289 ipr@ietf.org. 291 Thaler Expires August 2006 6