1 Can DHCP support mobility across LANs (on different subnets?)  On its own, the answer is NO; for reasons cited in DHCP talk on slide 9.  However, DHCP can be used in conjunction with mobile IP as explained on next few slides

2 Mobile IP care-of addresses  A foreign agent care-of address is acquired by a mobile when it hears an agent advertisement from a FA. In this mode, the FA is the end of the tunnel and does decapsulation.  Collocated care-of address is a local IP address acquired directly by the mobile through some means, such as DHCP or owned by mobile as a long-term address for its use only when visiting some foreign network. In this mode, mobile sends registration directly to HA and it is the end of the tunnel, perfoming decapsulation

3 Use of DHCP when a mobile changes subnets while communicating  If a mobile moves from an AP on one subnet to an AP on another subnet, it can use DHCP to acquire a second IP address, and then register this as a “collocated care-of address” with the router (DHCP server) that gave it its first IP address (which now becomes its “home”).  The old IP address should not be lost; so the new address can be stored as an “alias” for the wireless interface  Thus, the mobile will have two IP addresses  Since the communication session (say TCP) was started with the old address, packets will continue to arrive with the old address as the destination. The HA will perform encapsulation and tunnel packets to new address. The mobile will perform decapsulation and receive the packets.

4 Example MAX: finish this example; show Host A with a.46 address first. show a CN and data flow in a TCP connection; Change Host C to Host A (A moves); and so on; show tunneling + decapsulation). Access Point (AP) I R Access Point (AP) II Host AHost C DHCP SERVER Host B DHCP SERVER DHCP Discover Message DHCP RELAY

5 Example contd. Access Point (AP) I R Access Point (AP) II Host AHost C DHCP SERVER Host B DHCP SERVER DHCP OFFER DHCP RELAY

6 Example contd. Access Point (AP) I R Access Point (AP) II Host AHost C DHCP SERVER Host B DHCP SERVER DHCP REQUEST

7 Example contd. Access Point (AP) I R Access Point (AP) II Host AHost C DHCP SERVER Host B DHCP SERVER DHCP ACK