One document matched: draft-thaler-autoconf-multisubnet-manets-00.txt

Internet Draft                                                 D. Thaler 
February 25, 2006                                              Microsoft 
Expires August 2006                                                      
 
                          Multi-Subnet MANETs 
           <draft-thaler-autoconf-multisubnet-manets-00.txt> 

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Copyright Notice 

   Copyright (C) The Internet Society (2006).  All Rights Reserved. 

Abstract 

   This document describes an approach to addressing nodes in Mobile 
   Ad-hoc Networks (MANETs) which involves assigning a separate subnet 
   to each MANET router.  This approach avoids many of the problems 
   that arise in other approaches, and is intended to allow existing 
   protocols and applications to work unmodified. 

1. Introduction 

   A Mobile Ad-hoc Network (MANET) is one in which the topology may be 
   very dynamic, such as highly mobile nodes communicating over a 
   wireless medium.  In this document we assume that there are 
   forwarding nodes which participate in a MANET routing protocol.  
   Furthermore, we assume that there may also be non-MANET nodes 
   attached behind MANET forwarding nodes (e.g., via wired Ethernet).  
   We will use the term "MANET router" to refer to the first type of 
   nodes, and "client" to refer to the latter type of nodes. 

  
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   There are three general approaches to architecting the data 
   (forwarding) plane: 

   (A)  Treat the entire MANET as a single link, and do all forwarding 
        at the datalink-layer, exposing (say) normal Ethernet to IP.  
        The control plane thus consists of a layer-2 routing protocol.  
        In this approach, existing protocols and applications work 
        normally. 

   (B)  Treat the MANET as a single subnet composed of multiple links, 
        such that MANET routers must do layer-3 forwarding (decrement 
        TTL, etc.) between nodes in the same subnet.  The control plane 
        consists of a layer-3 MANET routing protocol.  This approach 
        has a number of problems as discussed in [MLSI], and may break 
        existing protocols and applications.  Clients are either not 
        supported at all, or some additional proxying method is 
        required. 

   (C)  Treat the MANET as a site containing many subnets, such that 
        MANET routers act as normal routers when forwarding data 
        between subnets.  The control plane consists of a layer-3 MANET 
        routing protocol, as with approach (B).  This approach avoids 
        most of the problems of (B), easily supports clients, and is 
        what the remainder of this document outlines. 

2. Overview 

   The MANET is treated as a site composed of many subnets.  Each MANET 
   router is assigned its own subnet prefix(es).  Each client is 
   assigned its own IP address(es) on a subnet assigned to a MANET 
   router to which it is attached. 

   The MANET site may or may not have external connectivity.  If there 
   is, then any site gateways are configured with the site prefix(es) 
   and advertise them into the external routing system, as normal site 
   gateways do.  If there is no external connectivity, then one or more 
   MANET routers are configured with the site prefix(es), e.g., a 
   Unique Local IPv6 Prefix [RFC4193], and 10/8 for IPv4 [RFC1918].  It 
   may be possible to automatically generate a site prefix for the site 
   in a zero-configuration MANET (e.g., by electing one node to do so), 
   but such a mechanism is outside the scope of this document. Note 
   that a /48 IPv6 site prefix results in the ability to support up to 
   2^16 MANET routers, plus any clients behind them. 

   Each router then uses a subnet allocation protocol to acquire one or 
   more subnet prefixes within the site prefix.  It then uses this 
   subnet prefix to number itself and any clients.   

   As a result, this approach needs only two MANET-specific protocols: 

        1) A routing protocol capable of exchanging subnet routes, and 

        2) A subnet allocation protocol capable of allocating prefixes. 
  
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   All other protocols and applications operate normally. 

3. Client Behavior 

   Clients operate with no changes, using normal IPv4 and IPv6 
   mechanisms. 

4. MANET Router Behavior 

4.1. Obtaining a subnet prefix 

   The requirements for a subnet allocation protocol are: 

   1) Must be capable of allocating a subnet prefix (not just a single 
      address). 

   2) Must prevent duplicate subnet prefix assignments. 

   3) Must handle network partitions and heals, due to the highly 
      dynamic nature of a MANET. 

   4) Must complete rapidly, with low overhead. 

   5) Must support a bootstrap scenario where all MANET routers without 
      a manually configured prefix attempt to allocate a prefix at the 
      same time. 

   6) Should support the ability to detect duplicate layer-2 addresses. 

   7) Should support the ability to detect a duplicate IPv6 link-local 
      address within the MANET site (since the dynamic nature means 
      that any other router may eventually be on the same link, this 
      helps avoid future conflicts). 

   Details of the actual subnet allocation protocol are outside the 
   scope of this draft.  At a high level, an address allocation 
   protocol proposed for a multilink-subnet approach (approach B) can 
   be modified to be suitable, by inclusion of a prefix length. 

4.2. Using a subnet prefix 

   One common practice in BGP is to assign a routable address to the 
   router's loopback interface, and use that for communication which 
   may be routed over different physical interfaces over time (e.g., to 
   survive failures). 

   In the same vein, a MANET router takes its allocated prefix, assigns 
   it to its loopback interface, and advertises it in the MANET routing 
   protocol.  If the MANET router also has a client interface (e.g., an 
   Ethernet link with wired clients attached), then the implementation 
   can either allocate a second subnet prefix for that link, or may 
   simply assign its sole subnet prefix to a client interface rather 
   than its loopback interface.  The MANET router then assigns its own 
  
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   IPv4 and/or IPv6 addresses on its loopback interface by using a 
   fixed address suffix (e.g., .1 in IPv4 and ::1 in IPv6).   

   The MANET router's other interfaces (e.g., a wireless interface used 
   to communicate with other MANET routers) is not given an IPv4 
   address (i.e., left unnumbered).  An IPv6 link-local address is 
   assigned per normal IPv6 stateless address autoconfiguration 
   [RFC2462].  Note that normal IPv6 Duplicate Address Detection may 
   occur as usual, but the MANET routers seen on that link will change 
   over time.  DAD need not be redone as long as the subnet allocation 
   protocol is responsible for detecting duplicate IPv6 link-local 
   addresses. 

   Applications running on the MANET router will use the loopback 
   interface, since that is the one with the global address on it.  All 
   other MANET nodes will appear to the application as being off-
   subnet. 

5. Security Considerations 

   Often the hardest attacks to defend against are on-link attacks 
   (e.g., ARP attacks in IPv4).  Unlike the other two approaches, this 
   approach narrows the set of nodes which are on-link to only those 
   nodes which are nearby, as opposed to being anywhere in the MANET.  
   In addition to mitigations in various protocols, this may make 
   social mitigations easier as well. 

   In addition, since this approach does not change the standard 
   address allocation and forwarding mechanisms in IPv4 and IPv6, it 
   avoids the security issues mentioned in [MLSI], resulting in a 
   potentially more secure environment than with a multilink subnet 
   approach. 

   The routing protocol in use must be secured to avoid attackers 
   misrouting packets.  The issues here are discussed in [RFC2501]. 

   The subnet allocation protocol in use must also be secured to avoid 
   attackers consuming all available subnet space, or preventing 
   legitimate MANET routers from obtaining a subnet prefix. 

6. IANA Considerations 

   This document has no actions for IANA. 

7. Acknowledgements 

   Suresh Krishnan first suggested assigning a subnet prefix to each 
   MANET node. 





  
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8. Normative References 

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

   [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address 
             Autoconfiguration", RFC 2462, December 1998. 

   [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 
             Addresses", RFC 4193, October 2005. 

9. Informative References 

   [MLSI]    Thaler, D., "Issues With Protocols Proposing Multilink 
             Subnets", draft-thaler-intarea-multilink-subnet-issues-
             00.txt, February 2006. 

   [RFC2501] Corson, S. and J. Macker, "Mobile Ad hoc Networking 
             (MANET): Routing Protocol Performance Issues and 
             Evaluation Considerations", RFC 2501, January 1999. 

Authors' Addresses 

   Dave Thaler 
   Microsoft 
   One Microsoft Way 
   Redmond, WA 98052 
   Phone: +1 425 703 8835 
   Email: dthaler@microsoft.com 























  
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