System Administration Guide: IP Services

Broadcast Datagrams

When a home agent receives a broadcast or multicast datagram, the home agent only forwards the datagram to mobile nodes that have specifically requested that they receive them. How the home agent forwards broadcast and multicast datagrams to mobile nodes depends primarily on two factors. Either that mobile node is using a foreign-agent provided care-of address, or the mobile node is using its own co-located care-of address. The former means that the datagram must be double encapsulated. The first IP header identifies the mobile node for which the datagram is to be delivered. Remember, this first IP header is not present in the broadcast or multicast datagram. The second IP header identifies the care-of address, and is the usual tunnel header. In the latter instance, the mobile node is de-capsulating its own datagrams, and the datagram needs only to be sent through the regular tunnel.