user manual

6-4
Cisco Aironet 1200 Series Access Point Software Configuration Guide
OL-2159-05
Chapter 6 Configuring Proxy Mobile IP
Introduction to Mobility in IP
Figure 6-2 The Mobile IP Environment
In order for a mobile node (MN) to successfully roam across subnets it must first be anchored to its home
network. The home agent (HA) is the router that serves as that anchor. The home agent contains a list of
all devices (by IP address) that are capable of roaming from its network. After the mobile node roams to
a new network, it must register with the home agent as being away from home. Its registration is sent by
way of the Foreign Agent (FA), the router providing service on the foreign network. The foreign agent
includes a care-of address in the registration it sends to the home agent. This address is used as the
termination address of the tunnel on the foreign router. A tunnel is then built between the home agent
and the foreign agent for all traffic destined for the mobile node.
When a mobile node sends traffic to another device (known as a correspondence node or correspondence
host), such as a web server, the outbound traffic is routed directly to the destination device. The
destination device replies to the source IP address, resulting in the the traffic being routed to the home
agent because it is the default router for the subnet from which the mobile node originated. The home
agent then forwards the traffic through the tunnel to the foreign agent, which forwards it to the mobile
node. Figure 6-3 provides an example of this process.
90541
CN
FA
HA
COA
MN
MN
Internet
HA, Home Agent
Maintains an association between
the MN's "home" IP address and its
care of address (loaned address) on
the foreign network
Redirects and tunnels packets to the
care of address on the foreign
network
MN, Mobile Node
An IP host that maintains network
connectivity using its "home" IP address,
regardless of which subnet (or network) it
is connected to
CN, Correspondent Node
Destination IP host in session with
a Mobile Node
FA, Foreign Agent
Provides an addressable point of
attachment to the MN Care Of
Address (COA)
Maintains an awareness for all
visiting MNs
Acts as a "relay" between the MN
and its Home Agent
Receives all packets for the MN
from the MN's Home Agent