 Information option. 9.1.2.5. ND protocol modifications The changes to the ICMPv6 ND (Neighbor Discovery) protocol are as follows: - the RA (Router Advertisement) message is modified; - the Prefix Information option is modified; - the Advertisement Interval option is created; - the Home Agent Information option is created. The H (Home Agent) flag is introduced in the Router Advertisement message to allow a home agent to discover other home agents on the home network. The RA message uses the LINK-LOCAL address as the source address. The Prefix Information option includes the prefix used to set up the GLOBAL UNICAST address. The home agent listening for Router Advertisement messages from other home agents cannot get their GLOBAL UNICAST address. The Prefix Information option introduces an R (Router Address) flag to signify that the announced prefix is actually a GLOBAL UNICAST address. S2c Tunnel Establishment The Advertisement Interval option is passed in the Router Advertisement message to set the frequency of sending messages. The Home Agent Information option is associated with the Router Advertisement message sent by the home agent. It specifies the level of preference of the home agent and its lifetime. The preference level is used by the home agent to order the home agent list transmitted in the message Home Agent Address Discovery Reply. 9.1.3. Procedures 9.1.3.1. Attachment of the mobile node to the home agent When the mobile node detects a network change, it performs the DAD (Duplicate Address Detection) procedure with its LINK-LOCAL address. It then discovers the network prefix by ICMPv6 messages, Router Solicitation and Router Advertisement; builds its CoA and verifies its uniqueness (Figure 9.3). Foreign network network 1 Router Solicitation 2 Router Advertisement Agent 3 Home Agent Address Discovery Request 4 - Home Agent Address Discovery Reply 5 Binding Update 6 Neighbor Advertisement Mobile 7 - Binding Acknowledgment Figure 9.3. Attachment of the mobile node to the home agent Sometimes, when the mo