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| 8.1 |  | Controlling Routing Update Traffic |
| 8.1.1 |  | Controlling routing updates |

Router RTA as shown in Figure , is running a simple distance vector routing protocol called RIP.

The RIP configuration command network 10.0.0.0 serves two functions. First, the command tells RIP where to send and receive advertisements, and on which interfaces to send and receive updates. 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, such as Bri0, S1, S2, and E1. 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 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. 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 therefore glean key network information.

For these reasons, it is necessary to configure passive interfaces or route filters to control routing updates. Both strategies are discussed in the following sections.