|
Consider RTA in the figure, which is running a simple
distance-vector routing protocol, RIP.
The
network 10.0.0.0
command does two things. First, it tells RIP where to send
and receive advertisements (which interfaces to send and receive
updates on). The
network 10.0.0.0 command
enables RIP updates on all interfaces that have an IP address
belonging to the 10.0.0.0 network (Bri0, S1, S2, and E0). Second,
this command tells the RIP process what to advertise. All
directly connected subnets belonging to the major network 10.0.0.0
are included in RIP updates, in addition to any dynamically learned
routes. That means that RTA advertises the following networks:
10.1.1.0, 10.2.2.0, 10.3.3.0, and 10.4.4.0.
Unfortunately, the default behavior of RIP, or any routing
protocol, may not be the best thing for an internetwork. Look again
at the figure. Is it useful for RTA to send updates on all four
interfaces?
Updating out E0 is a waste of resources. No other routers on the
10.4.4.0 subnetwork can receive the updates, so they serve no
purpose. Meanwhile, sending updates creates slight (and needless)
overhead and a potential security risk. (A malicious user could use
a packet sniffer to capture routing updates and thus glean key
network information.)
For these reasons, you can configure passive interfaces or route
filters to control routing updates. Both strategies are discussed in
the following sections.
|
|