11

Can DHCP support mobility across 802.11 Can DHCP support mobility across 802.11 LANs (on different subnets?)LANs (on different subnets?)

On its own, the answer is NO; for reasons On its own, the answer is NO; for reasons cited in DHCP talk on slide 9.cited in DHCP talk on slide 9.

However, DHCP can be used in However, DHCP can be used in conjunction with mobile IP as explained on conjunction with mobile IP as explained on next few slidesnext few slides

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Mobile IP care-of addressesMobile IP care-of addresses

A foreign agent care-of address is acquired by a A foreign agent care-of address is acquired by a mobile when it hears an agent advertisement mobile when it hears an agent advertisement from a FA. In this mode, the FA is the end of the from a FA. In this mode, the FA is the end of the tunnel and does decapsulation.tunnel and does decapsulation.

Collocated care-of address is a local IP address Collocated care-of address is a local IP address acquired directly by the mobile through some acquired directly by the mobile through some means, such as DHCP or owned by mobile as a means, such as DHCP or owned by mobile as a long-term address for its use only when visiting long-term address for its use only when visiting some foreign network. In this mode, mobile some foreign network. In this mode, mobile sends registration directly to HA and it is the end sends registration directly to HA and it is the end of the tunnel, perfoming decapsulationof the tunnel, perfoming decapsulation

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Use of DHCP when a mobile changes Use of DHCP when a mobile changes subnets while communicatingsubnets while communicating

If a mobile moves from an AP on one subnet to an AP on 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 another subnet, it can use DHCP to acquire a second IP address, and then register this as a “collocated care-of address, and then register this as a “collocated care-of address” with the router (DHCP server) that gave it its address” with the router (DHCP server) that gave it its first IP address (which now becomes its “home”).first IP address (which now becomes its “home”). The old IP address should not be lost; so the new address can The old IP address should not be lost; so the new address can

be stored as an “alias” for the wireless interfacebe stored as an “alias” for the wireless interface Thus, the mobile will have two IP addressesThus, the mobile will have two IP addresses Since the communication session (say TCP) was started with Since the communication session (say TCP) was started with

the old address, packets will continue to arrive with the old the old address, packets will continue to arrive with the old address as the destination. The HA will perform encapsulation address as the destination. The HA will perform encapsulation and tunnel packets to new address. The mobile will perform and tunnel packets to new address. The mobile will perform decapsulation and receive the packets.decapsulation and receive the packets.

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Example MAX: finish this example; show Example MAX: finish this example; show Host A with a .46 address first. show a CN Host A with a .46 address first. show a CN and data flow in a TCP connection; Change and data flow in a TCP connection; Change

Host C to Host A (A moves); and so on; Host C to Host A (A moves); and so on; show tunneling + decapsulation). show tunneling + decapsulation).

Access Point (AP) I R Access Point (AP) II128.238.46 128.238.43

Host A Host C

DHCP SERVER

Host B

128.238.45DHCP SERVER

DHCP Discover Message

128.238.54

DHCP RELAY

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Example contd.Example contd.

Access Point (AP) I R Access Point (AP) II128.238.46 128.238.43

Host A Host C

DHCP SERVER

Host B

128.238.45DHCP SERVER

DHCP OFFER

DHCP OFFER

DHCP RELAY

128.238.54

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Example contd.Example contd.

Access Point (AP) I R Access Point (AP) II128.238.46 128.238.43

Host A Host C

DHCP SERVER

Host B

128.238.45DHCP SERVER DHCP

REQUEST

128.238.54

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Example contd.Example contd.

Access Point (AP) I R Access Point (AP) II128.238.46 128.238.43

Host A Host C

DHCP SERVER

Host B

128.238.45DHCP SERVER

128.238.54 DHCP ACK