 is equal to 434 for the message Registration Request transmitted by the mobile node (respectively for the response Registration Reply of the home agent). 8.3.4. Procedure Foreign agents announce their presence using ICMPv4 message Agent Advertisement. A mobile node may optionally request an ICMPv4 message Agent Advertisement through a foreign agent solicitation message. A mobile node receives these Agent Advertisement messages and determines whether it is on its home network or on a foreign network. When the mobile node detects that it is located on its home network, it operates without the mobility services. When a mobile node detects that it has moved to a foreign network, it obtains a CoA, determined from the Agent Advertisement message, or through a DHCP server. The mobile node then registers its CoA with its home agent through the exchange of Registration Request and Registration Reply messages, possibly via a foreign agent. When the home agent receives and accepts the Registration Request message, it broadcasts a gratuitous ARP (Address Resolution Protocol) message to update the ARP table of the hosts on its network, matching the Ethernet address of the home agent with the HoA. Similarly, the home agent provides the ARP proxy function to respond to the ARP requests that it receives from hosts in the network regarding the HoA. S2a/S2b Tunnel Establishment Packets sent by the correspondent node to the HoA are intercepted by the home agent. The home agent establishes a tunnel and transfers the packets to the CoA. If the CoA is obtained by the Agent Advertisement message, the end of the tunnel is constituted by the foreign agent that delivers the packets to the mobile node (Table 8.2 and Figure 8.8). In the case where the CoA is obtained by a DHCP server, the mobile node constitutes the tunnel termination. The correspondent node sends packets to the mobile node Packet source address Packet destination address The home agent establishes the tunnel with the mobile node Tunnel source address Tunnel destination ad