Mobile IP Administration Guide

Routing Datagrams to and From Mobile Nodes

This section describes how mobile nodes, home agents, and foreign agents cooperate to route datagrams to and from mobile nodes that are connected to a foreign network.

Encapsulation Types

Home agents and foreign agents support tunneling datagrams using one of the available encapsulation methods (IP in IP Encapsulation, Minimal Encapsulation, or Generic Routing Encapsulation). Mobile nodes that use a co-located care-of address can receive tunneled datagrams using any encapsulation type.

Unicast Datagram Routing

When registered on a foreign network, the mobile node chooses a default router using the following rules:

Broadcast Datagrams

When a home agent receives a broadcast datagram, it does not forward the datagram to any mobile nodes in its mobility binding list. However, the home agent does forward the datagram if a mobile node has requested forwarding of broadcast datagrams. For each registered mobile node, the home agent forwards received broadcast datagrams to the mobile node; the method depends on how the configuration of the home agent specifies categories of broadcast datagrams forwarded to mobile nodes.

Multicast Datagram Routing

To receive multicasts, a mobile node joins the multicast group in one of the following ways:

A mobile node that sends datagrams to a multicast group also has the following options:

Multicast routing depends on the IP source address. Therefore, a mobile node that sends multicast datagrams directly on the visited network uses a co-located care-of address as the IP source address. Similarly, a mobile node that tunnels a multicast datagram to its home agent uses its home address as the IP source address of both the multicast datagram and the encapsulating datagram. This second option assumes that the home agent is a multicast router.