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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

Solomon Standards Track [Page 1] RFC 2005 Mobile IP Applicability Statement October 1996

  1. - a topologically significant address – to which standard IP

routing mechanisms can deliver packets.

 The Mobile IP protocol defines the following:
  1. an authenticated registration procedure by which a mobile node

informs its home agent(s) of its care-of address(es);

  1. an extension to ICMP Router Discovery [RFC1256] which allows mobile

nodes to discover prospective home agents and foreign agents; and

  1. 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.

Solomon Standards Track [Page 2] 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:

Solomon Standards Track [Page 3] 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.

Solomon Standards Track [Page 4] 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

Solomon Standards Track [Page 5]

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