Mobile IP ( Mobile IP )

• 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 which allows mobile nodes to discover prospective home agents and foreign agents.


• The rules for routing packets to and from mobile nodes, including the specification of one mandatory tunneling mechanism and several optional tunneling mechanisms.

• Agent Discovery
  Home agents and foreign agents may advertise their availability on each link for which they provide service. A newly arrived mobile node can send a solicitation on the link to learn if any prospective agents are present.



• Registration
  When the mobile node is away from home, it registers its care-of address with its home agent. Depending on its method of attachment, the mobile node will register either directly with its home agent, or through a foreign agent which forwards the registration to the home agent.



• Silently discard
  The implementation discards the datagram without further processing, and without indicating an error to the sender. The implementation should provide the capability of logging the error, including the contents of the discarded datagram, and should record the event in a statistics counter.

Mobility agents (i.e., foreign agents and home agents) advertise their presence via Agent Advertisement messages. A mobile node may optionally solicit an Agent Advertisement message from any locally attached mobility agents through an Agent Solicitation message.

A mobile node receives these Agent Advertisements and determines whether it is on its home network or a foreign network.

When the mobile node detects that it is located on its home network, it operates without mobility services. If returning to its home network from being registered elsewhere, the mobile node deregisters with its home agent, through exchange of a Registration Request and Registration Reply message with it.

When a mobile node detects that it has moved to a foreign network, it obtains a care -of address on the foreign network. The care -of address can either be determined from a foreign agent's advertisements (a foreign agent care-of address), or by some external assignment mechanism such as DHCP (a co- located care-of address).

The mobile node operating away from home then registers its new care-of address with its home agent through exchange of a Registration Request and Registration Reply message with it, possibly via a foreign agent.

Datagrams sent to the mobile node's home address are intercepted by its home agent, tunneled by the home agent to the mobile node's care-of address, received at the tunnel endpoint (either at a foreign agent or at the mobile node itself), and finally delivered to the mobile node.

In the reverse direction, datagrams sent by the mobile node are generally delivered to their destination using standard IP routing mechanisms, not necessarily passing through the home agent.

• A "foreign agent care-of address" is a care-of address provided by a foreign agent through its Agent Advertisement messages. In this case, the care-of address is an IP address of the foreign agent. In this mode, the foreign agent is the endpoint of the tunnel and, upon receiving tunneled datagrams, decapsulates them and delivers the inner datagram to the mobile node. This mode of acquisition is preferred because it allows many mobile nodes to share the same care-of address and therefore does not place unnecessary demands on the already limited IPv4 address space.



• A "co-located care-of address" is a care-of address acquired by the mobile node as a local IP address through some external means, which the mobile node then associates with one of its own network interfaces. The address may be dynamically acquired as a temporary address by the mobile node such as through DHCP, or may be owned by the mobile node as a long-term address for its use only while visiting some foreign network. Specific external methods of acquiring a local IP address for use as a co-located care-of address are beyond the scope of this document. When using a co-located care-of address, the mobile node serves as the endpoint of the tunnel and itself performs decapsulation of the datagrams tunneled to it.

              2) Datagram is intercepted   3) Datagram is

                 by home agent and            detunneled and

                 is tunneled to the           delivered to the

                 care-of address.             mobile node.



                   +-----+          +-------+         +------+

                   |home | =======> |foreign| ------> |mobile|

                   |agent|          | agent | <------ | node |

                   +-----+          +-------+         +------+

   1) Datagram to    /|         /

      mobile node     |        /   4) For datagrams sent by the

      arrives on      |      /        mobile node, standard IP

      home network    |    /          routing delivers each to its

      via standard    |  |_           destination.  In this figure,

      IP routing.   +----+            the foreign agent is the

                    |host|            mobile node's default router.

                    +----+

Type	Length	Description
0		One byte padding.
1		Registration request.
2
3		Registration reply.
4		MIP Tunnel Data Message.
56
7		Registration Revocation.
8-14
15		Revocation Acknowledgment.
16		Mobility Agent Advertisement.
1718
19		Prefix-Lengths.
20-23
24		Challenge Extension.
25-31
32		Mobile-Home authentication.
33		Mobile-Foreign authentication.
34		Foreign-Home authentication.
35
36		Generalized Mobile IP Authentication.
37
38		CVSE, Critical Vendor/Organization Specific Extension.
39
40		MN-FA-KeyGen Request.
41		MN-FA-KeyGen Reply.
42		MN-HA-KeyGen Request.
43		MN-HA-KeyGen Reply.
44	6	UDP Tunnel Reply Extension.
45-126
127		Non-skippable Extension for Experimental use.
128		Deprecated (2001 Aug 31).
129		SKIP Firewall Traversal Extension.
130		Encapsulating Delivery Style Extension.
131		Mobile Node NAI.
132		MN-FA Challenge Extension.
133
134		NVSE, Normal Vendor/Organization Specific Extension.
135
136		NAI Carrying Extension.
137	1+	Revocation Support.
138		CARD Request option.
139		CARD Reply option.
140-143
144	6	UDP Tunnel Request Extension.
145-254
255		Message for Experimental use.

• Mobility Header
  Mobile IPv6 defines a new IPv6 protocol, using the Mobility Header. This Header is used to carry the following messages:
  
  • Home Test Init
    A mobile node sends a Home Test Init message to the correspondent node (via the home agent) to acquire the home keygen token.
  
  
  
  • Home Test
    The Home Test message is sent in response to a Home Test Init message. It is sent via the home agent.
  
  
  
  • Care-of Test Init
    The mobile node sends a Care-of Test Init message to the correspondent node (directly, not via the home agent) to acquire the care-of keygen token.
  
  
  
  • Care-of Test
    These four messages are used to perform the return routability procedure from the mobile node to a correspondent node. This ensures authorization of subsequent Binding Updates.
  
  
  
  • Binding Update
    A Binding Update is used by a mobile node to notify a correspondent node or the mobile node's home agent of its current binding. The Binding Update sent to the mobile node's home agent to register its primary care-of address is marked as a "home registration".
  
  
  
  • Binding Acknowledgement
    A Binding Acknowledgement is used to acknowledge receipt of a Binding Update, if an acknowledgement was requested in the Binding Update, the binding update was sent to a home agent, or an error occurred.
  
  
  
  • Binding Refresh Request
    A Binding Refresh Request is used by a correspondent node to request a mobile node to re-establish its binding with the correspondent node. This message is typically used when the cached binding is in active use but the binding's lifetime is close to expiration. The correspondent node may use, for instance, recent traffic and open transport layer connections as an indication of active use.
  
  
  
  • Binding Error
    The Binding Error is used by the correspondent node to signal an error related to mobility, such as an inappropriate attempt to use the Home Address destination option without an existing binding.
  
  
  
• New IPv6 ICMP Messages
  Mobile IPv6 also introduces four new ICMP message types, two for use in the dynamic home agent address discovery mechanism, and two for renumbering and mobile configuration mechanisms. The following two new ICMP message types are used for home agent address discovery:


• Home Agent Address Discovery Request.



• Home Agent Address Discovery Reply.


The next two message types are used for network renumbering and address configuration on the mobile node:

• Mobile Prefix Solicitation.



• Mobile Prefix Advertisement.



• Site-Local Addressability
  This specification requires that home and care -of addresses must be unicast routable addresses. Site-local addresses may be usable on networks that are not connected to the Internet, but this specification does not define when such usage is safe and when it is not. Mobile nodes may not be aware of which site they are currently in, it is hard to prevent accidental attachment to other sites, and ambiguity of site-local addresses can cause problems if the home and visited networks use the same addresses. Therefore, site-local addresses should not be used as home or care-of addresses.

Example 1: Registering with a Foreign Agent Care-of Address



The mobile node receives an Agent Advertisement from a foreign agent and wishes to 

register with that agent using the advertised foreign agent care-of address. The mobile 

node wishes only IP-in-IP encapsulation, does not want broadcasts, and does not want 

simultaneous mobility bindings:



          IP fields:

            Source Address = mobile node's home address

            Destination Address = copied from the IP source address of the

              Agent Advertisement

            Time to Live = 1



          UDP fields:

            Source Port = 

            Destination Port = 434



          Registration Request fields:

            Type = 1

            S=0,B=0,D=0,M=0,G=0

            Lifetime = the Registration Lifetime copied from the

              Mobility Agent Advertisement Extension of the

              Router Advertisement message

            Home Address = the mobile node's home address

            Home Agent = IP address of mobile node's home agent

            Care-of Address = the Care-of Address copied from the

              Mobility Agent Advertisement Extension of the

              Router Advertisement message

            Identification = Network Time Protocol timestamp or Nonce



          Extensions:

            An authorization-enabling extension (e.g., the Mobile-Home Authentication 

          Extension)

Example 2: Registering with a Co-Located Care-of Address



The mobile node enters a foreign network that contains no foreign agents. The mobile 

node obtains an address from a DHCP server for use as a co-located care-of address. 

The mobile node supports all forms of encapsulation (IP-in-IP, minimal encapsulation, 

and GRE), desires a copy of broadcast datagrams on the home network, and does not 

want simultaneous mobility bindings:



          IP fields:

            Source Address = care-of address obtained from DHCP server

            Destination Address = IP address of home agent

            Time to Live = 64



          UDP fields:

            Source Port = 

            Destination Port = 434



          Registration Request fields:

            Type = 1

            S=0,B=1,D=1,M=1,G=1

            Lifetime = 1800 (seconds)

            Home Address = the mobile node's home address

            Home Agent = IP address of mobile node's home agent

            Care-of Address = care-of address obtained from DHCP server

            Identification = Network Time Protocol timestamp or Nonce



          Extensions:

            The Mobile-Home Authentication Extension

Example 3: Deregistration



The mobile node returns home and wishes to deregister all care-of addresses with its 

home agent.



          IP fields:

            Source Address = mobile node's home address

            Destination Address = IP address of home agent

            Time to Live = 1

          UDP fields:

            Source Port = 

            Destination Port = 434

          Registration Request fields:

            Type = 1

            S=0,B=0,D=0,M=0,G=0

            Lifetime = 0

            Home Address = the mobile node's home address

            Home Agent = IP address of mobile node's home agent

            Care-of Address = the mobile node's home address

            Identification = Network Time Protocol timestamp or Nonce



          Extensions:

            An authorization-enabling extension (e.g., the Mobile-Home Authentication 

          Extension)

■ Parent layer
■ Child layer

UDP

Mobile IP