150 Chapter 7: Metro Mobility: Cisco Mobile Networks
successful registration with its Home Agent, the mobile router does not need to include the
NVSE in reregistrations if the status of the mobile networks has not changed. However, if there
are any changes to the status of the dynamic mobile networks registered with the Home Agent,
the mobile router sends a RRQ with an NVSE, either deleting or adding the appropriate mobile
networks.
In response to a RRQ with the Mobile Router Dynamic Mobile Network NVSE appended, the
mobile router expects to receive a RRP from its Home Agent acknowledging all the mobile
networks associated with the mobile router. Specifically, it expects to see a RRP with the
Mobile Router Dynamic Mobile Network NVSE describing its dynamic mobile networks, and
a Mobile Router Static Mobile Network NVSE describing its static mobile networks, if any
exist. Such a RRP serves as an acknowledgment to the mobile router that the Home Agent has
indeed processed its mobile networks properly.
If the mobile network is a routed network, that is, other routers are attached to the mobile
network interface, it requires static network configuration. When examining the configuration,
it will be clear that this is the case because dynamic networks are learned from the interface
configuration. It might seem odd to have a routed network attached to a mobile router, but it is
not unheard of. For example, a large cruise ship might already have a routed network
infrastructure on board and might be retrofitted with a mobile router to take advantage of
multiple link types to provide passengers with optimal connectivity at a minimal cost.
Configuration of Mobile Router and Its Mobile Networks
The mobile router must first be configured as a Mobile Node. Its mobile networks are then
either statically configured, or the mobile router is configured to send its mobile networks
dynamically during the Mobile IP registration process.
Because the mobile router is a Mobile Node, it requires the same basic configuration as we have
previously seen with Mobile Nodes. The mobile router requires the use of a static Home
Address and does not support the use of a Network Access Identifier (NAI) or dynamic
addressing. This Home Address must be configured on an interface and then identified in the
mobile router configuration. Although you can configure the Home Address on a physical
interface and use a physical Home Network, numerous problems arise. For example, physical
interfaces do not allow a 32-bit subnet mask to be configured. Thus, when the mobile router is
not attached to its physical Home Network, it cannot reach other devices on its Home Network
because it identifies them as being directly connected. Also, if the Home Address is on a
physical interface and that interface is down, the mobile router cannot receive tunneled packets.
The Home Address should be configured on a loopback interface, and a 32-bit mask should be
applied to the address. The mask of the Home Network is identified in the mobile router
configuration section. The Home Network should be configured as a virtual network on the
Home Agent.

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