Configuring IP Routing
Configuring the MultiVoice Gateway for dynamic route updates
MultiVoice Gateway for the MAX— User’s Guide
Preliminary November 23, 1998
8-21
Ignoring the default route
You can configure the MultiVoice Gateway to ignore default routes advertised by routing
protocols. This configuration is recommended, because you typically do not want the default
route changed by a RIP update. The default route specifies a static route to another IP router,
which is often a local router such as a Cisco router or another kind of LAN router. When the
MultiVoice Gateway is configured to ignore the default route, RIP updates will not modify the
default route in the MultiVoice Gateway routing table.
RIP Policy and RIP Summary
The RIP Policy and RIP Summary parameters have no affect on RIP-v2.
If the MultiVoice Gateway is running RIP-v1, the RIP Policy parameter specifies a split
horizon or poison reverse policy to handle update packets that include routes that were
received on the same interface on which the update is sent. Split-horizon means that the
MultiVoice Gateway does not propagate routes back to the subnet from which they were
received. Poison-reverse means that it propagates routes back to the subnet from which they
were received, but with a metric of 16.
The RIP Summary parameter specifies whether to summarize subnet information when
advertising routes. If the MultiVoice Gateway summarizes RIP routes, it advertises a route to
all the subnets in a network of the same class. For example, the route to 200.5.8.13/28 (a class
C address subnetted to 28 bits) would be advertised as a route to 200.5.8.0. When the
MultiVoice Gateway does not summarize information, it advertises each route in its routing
table as-is. In the example just given, the MultiVoice Gateway would advertise a route only to
200.5.8.13.
Ignoring ICMP Redirects
ICMP was designed to dynamically find the most efficient IP route to a destination. ICMP
Redirect packets are one of the oldest route discovery methods on the Internet. They are also
ne of the least secure methods, because it is possible to counterfeit ICMP Redirects and change
the way a device routes packets.
Examples of RIP and ICMP configurations
The following sample configuration instructs the router to ignore ICMP redirect packets, and
to receive (but not send) RIP updates on the Ethernet interface.
1
Open Ethernet > Mod Config > Ether Options.
2
Configure the router to receive (but not send) RIP updates on Ethernet:
Ethernet
Mod Config
Ether options…
RIP=Recv-v2
Receiving RIP updates on Ethernet means that the router will learn about networks that
are reachable through other local routers. However, it will not propagate information
about all of its remote connections to the local routers.
3
Close the Ether Options subprofile, and set ICMP Redirects to Ignore.
ICMP Redirects=Ignore