Network Working Group                                         J. Solomon
Request for Comments: 2005                                      Motorola
Category: Standards Track                                   October 1996

            Applicability Statement for IP Mobility Support

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   As required by [RFC 1264], this report discusses the applicability of
   Mobile IP to provide host mobility in the Internet.  In particular,
   this document describes the key features of Mobile IP and shows how
   the requirements for advancement to Proposed Standard RFC have been

1. Protocol Overview

   Mobile IP provides an efficient, scalable mechanism for node mobility
   within the Internet.  Using Mobile IP, nodes may change their point-
   of-attachment to the Internet without changing their IP address.
   This allows them to maintain transport and higher-layer connections
   while moving.  Node mobility is realized without the need to
   propagate host-specific routes throughout the Internet routing
   fabric.  The protocol is documented in [MIP-PROTO].

   In brief, Mobile IP routing works as follows.  Packets destined to a
   mobile node are routed first to its home network -- a network
   identified by the network prefix of the mobile node's (permanent)
   home address.  At the home network, the mobile node's home agent
   intercepts such packets and tunnels them to the mobile node's most
   recently reported care-of address.  At the endpoint of the tunnel,
   the inner packets are decapsulated and delivered to the mobile node.
   In the reverse direction, packets sourced by mobile nodes are routed
   to their destination using standard IP routing mechanisms.

   Thus, Mobile IP relies on protocol tunneling to deliver packets to
   mobile nodes that are away from their home network.  The mobile
   node's home address is hidden from routers along the path from the
   home agent to the mobile node due to the presence of the tunnel.  The
   encapsulating packet is destined to the mobile node's care-of address

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RFC 2005           Mobile IP Applicability Statement        October 1996

   -- a topologically significant address -- to which standard IP
   routing mechanisms can deliver packets.

   The Mobile IP protocol defines the following:

   - an authenticated registration procedure by which a mobile node
     informs its home agent(s) of its care-of address(es);

   - an extension to ICMP Router Discovery [RFC1256] which allows mobile
     nodes to discover prospective home agents and foreign agents; and

   - the rules for routing packets to and from mobile nodes, including
     the specification of one mandatory tunneling mechanism ([MIP-IPinIP])
     and several optional tunneling mechanisms ([MIP-MINENC] and

2. Applicability

   Mobile IP is intended to solve node mobility across changes in IP
   subnet.  It is just as suitable for mobility across homogeneous media
   as it is for mobility across heterogeneous media.  That is, Mobile IP
   facilitates node movement from one Ethernet segment to another as
   well as it accommodates node movement from an Ethernet segment to a
   wireless LAN.

   One can think of Mobile IP as solving the "macro" mobility management
   problem.  It is less well suited for more "micro" mobility management
   applications -- for example, handoff amongst wireless transceivers,
   each of which covers only a very small geographic area.  In this
   later situation, link-layer mechanisms for link maintenance (i.e.
   link-layer handoff) might offer faster convergence and less overhead
   than Mobile IP.

   Mobile IP scales to handle a large number of mobile nodes in the
   Internet.  Without route optimization as described in [MIP-OPTIM],
   however, the home agent is a potential load point when serving many
   mobile nodes.  When home agents become overburdened, additional home
   agents can be added -- and even dynamically discovered by mobile
   nodes -- using mechanisms defined in the Mobile IP documents.

   Finally, it is noted that mobile nodes are assigned (home) IP
   addresses largely the same way in which stationary hosts are assigned
   long-term IP addresses; namely, by the authority who owns them.
   Properly applied, Mobile IP allows mobile nodes to communicate using
   only their home address regardless of their current location.  Mobile
   IP, therefore, makes no attempt to solve the problems related to
   local or global, IP address, renumbering.

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RFC 2005           Mobile IP Applicability Statement        October 1996

3. Security

   Mobile IP mandates the use of cryptographically strong authentication
   for all registration messages exchanged between a mobile node and its
   home agent.  Optionally, strong authentication can be used between
   foreign agents and mobile nodes or home agents.  Replay protection is
   realized via one of two possible mechanisms -- timestamps or nonces.

   Due to the unavailability of an Internet key management protocol,
   agent discovery messages are not required to be authenticated.

   All Mobile IP implementations are required to support, at a minimum,
   keyed MD5 authentication with manual key distribution.  Other
   authentication and key distribution algorithms may be supported.

   Mobile IP defines security mechanisms only for the registration
   protocol.  Implementations requiring privacy and/or authentication of
   data packets sent to and from a mobile node should use the IP
   security protocols described in RFCs 1827 and 1826 for this purpose.

4. MIB

   At the time of publication of this Applicability Statement, a
   Management Information Base (MIB) for Mobile IP has been written and
   documented in RFC 2006.

5. Implementations

   Several implementations of Mobile IP are known to exist.  The
   following list gives the origin and a contact for several such

      Organization:   Contact:

      CMU             Dave Johnson <>
      FTP Software    Frank Kastenholz <>
      IBM             Charlie Perkins <>
      Motorola        Jim Solomon <>
      Nokia           Gunyho Gabor <>
      SUN             Gabriel Montenegro <gab@cali.Eng.Sun.COM>
      Telxon          Frank Ciotti <>

6. Implementation Experience

   FTP Software hosted an interim meeting, October 23-27, 1995 in which
   interoperability of several implementations was demonstrated.  The
   following major features of the Mobile IP protocol were tested:

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RFC 2005           Mobile IP Applicability Statement        October 1996

   1)  Mobile Nodes receiving and processing Agent Advertisements.
   2)  Agents receiving Agent Solicitations and responding with Agent
   3)  Mobile Nodes registering with foreign agents on foreign networks.
   4)  Packets being received by the mobile node after having been
       tunneled by the home agent and de-tunneled by the foreign agent.
   5)  Packets from the mobile node being routed directly to their
   6)  Mobile nodes discovering that their connectivity/subnet had
       changed and re-registering at their new location.
   7)  Mobile nodes discovering that their current foreign agent had
       rebooted and therefore re-registering with that foreign agent.
   8)  The required form of tunneling (IP-in-IP encapsulation
       [MIP-IPinIP]) as well as the one of the optional forms of tunneling;
       namely, Minimal Encapsulation [MIP-MINENC].
   9)  Mobile nodes de-registering upon returning to their home network.
   10) Registrations being rejected for authentication failures,
       including invalid authenticators as well as mismatched
       identification values (replay protection).
   11) TCP connections remaining open (with data flowing) while a mobile
       node moved from its home network to a foreign network and then
       back again to the home network.

   Interoperability of at least two independent implementations was
   demonstrated for all of the features listed above.

7. Summary

   The co-chairs, on behalf of the working group participants, believe
   that the Mobile IP working group has satisfied the requirements set
   forth in [RFC1264] for the advancement of Mobile IP to Proposed
   Standard RFC.  Specifically, the technical specification document is
   stable, a MIB has been written, the security architecture has been
   set forth in accordance with IAB principles, and several independent
   implementations have been demonstrated to be interoperable.

8. References

   [RFC1256] Deering, S., Editor, "ICMP Router Discovery Messages", RFC
      1256, September 1991.

   [RFC1701] Hanks, S. et. al., "Generic Routing Encapsulation (GRE)",
      RFC 1701, October 1994.

   [RFC1264] Hinden, R., "Internet Routing Protocol Standardization
      Criteria", RFC 1264, October 1991.

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RFC 2005           Mobile IP Applicability Statement        October 1996

   [MIP-IPinIP] Perkins, C., Editor, "IP Encapsulation within IP",
      RFC 2003, October 1996.

   [MIP-OPTIM] Johnson, D., and C. Perkins, "Route Optimization in
      Mobile IP", Work in Progress.

   [MIP-PROTO] Perkins, C., Editor, "IP Mobility Support", RFC 2002,
      October 1996.

   [MIP-MINENC] Perkins, C., Editor, "Minimal Encapsulation within IP",
      RFC 2004, October 1994.

9. Author's Address

   Questions about this memo can be directed to:

   Jim Solomon
   Motorola Inc.
   1301 E. Algonquin Rd. - Rm 2240
   Schaumburg, IL  60196

   Voice:  +1-847-576-2753
   Fax:    +1-847-576-3240

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