user manual

6-3
Cisco Aironet 1200 Series Access Point Software Configuration Guide
OL-2159-05
Chapter 6 Configuring Proxy Mobile IP
Introduction to Mobility in IP
The Nomadic Approach
A nomadic node is a device that moves, or roams from one network to another. In order to use that
network, the device must renew its IP address and re-establish connectivity to any applications that were
in progress. There are advantages and disadvantages to the nomadic approach.
ISPs treat all devices as nomads. This means that any device requiring connectivity must request an IP
address through DHCP and be assigned a routable address that falls within the range assigned to that
service provider. After an address is assigned, the user can connect to the Internet and perhaps run a
Virtual Private Network (VPN) on top of the connection to obtain secured access to private networks.
Although this scheme provides mobility in the sense that a user can move from place to place and
connect to a public network, it does not maintain any sessions that are in progress. Also, the user is aware
that a change in network service has occurred.
The advantage to being a nomad is that service is available at a number of locations from a number of
providers. A disadvantage is that the process of connecting to that network is manual and sometimes
cumbersome. In addition, many applications do not run well when an IP address changes or a lengthy
connectivity timeout occurs.
The Mobile Approach
In contrast, a mobile node is a device that moves from one network to another while keeping its original
IP address. This arrangement has an additional advantage of having many applications continue
uninterrupted as long as the brief delay involved in roaming does not prompt a disconnect.
The major advantage of being a mobile node is that the device can now cross Layer 3 boundaries and,
through a tunnel back to the a router on its home network, have its traffic forwarded to it. This tunnel
back allows the device to keep its original IP address even though that address is no longer valid for the
subnet to which it has roamed.
Mobile IP Explained
A clear understanding of proxy Mobile IP requires a foundation knowledge of Mobile IP. Figure 6-2
identifies the components and explains the terminology used in Mobile IP.