Understanding the network.pdf - Back to Home

Configuring Dynamic IGP and EGP IP Routing
Protocols
All dynamic IP routing protocols are configured as IOS subprocesses, much the
same way a router interface is configured. The
global configuration command enables the process:
asbr-a1#config t
asbr-a1(configure)#router ospf 89
asbr-a1(config-router)#network 172.16.0.0 0.0.255.255 area 0.0.0.0
asbr-a1(config-router)#
After a process is enabled, it does not become active until a statement that corresponds to a configured router interface is added to
the subprocess.
After the process is configured, you need to add each directly connected network
that you wish the protocol to announce. If the network is not addedto the process,
it will not be announced by the protocol. Occasionally, you might want to receive,
but not send, network announcements on an interface (and you still want the
network announced by the routing process). This is common when a routing
protocol is used to manage a "private" network that is attached to an Internet
gateway, which is also using a routing protocol. In situations like this, the interface
can be run in passive mode using the routing configuration subprocess command
:
asbr-a1#config t
asbr-a1(configure)#router ospf 89
asbr-a1(config-router)# passive-interface s1
After the interface is in passive mode, it will only receive routing announcements.
When a router interface has been configured to operate in passive mode, it will only
accept routing announcements. This option is useful when you only want the router
to obtain reachability information, but not announce. Initially, this might seem odd,
this is a common practice in situations where data services are being provided by an
outside network (for example, Internet Gateway or News Service feed). In these
situations, the provider will use a static route to reach your gateway, but otherwise,