d show how to configure them for the most typical scenarios. There is no right or wrong way to configure routing proto- cols, though some ways are certainly better than others. When designing any network, remember that simplicity is a worthy goal that will save you countless hours of trou- bleshooting misery. RIP is the simplest of the routing protocols in use today. While I like to tell my clients that simple is good, I don't consider RIP to be simple goodness. RIP broadcasts all the routes it knows about every 30 seconds, regardless of the statuses of any other routers in the network. Because RIP uses broadcasts, every host on the network listens to the updates, even though few can process them. On larger networks, the updates can be quite large and consume a lot of bandwidth on expensive WAN links. Another issue with RIP is the fact that it does not use triggered updates. A triggered update is one that is sent when the network changes; nontriggered (timed) updates are sent on a regular schedule. Coupled with the fact that updates are sent only every 30 seconds, this behavior causes RIP networks to converge very slowly. Slow convergence is not acceptable in most modern networks, which require failover and convergence in seconds. A RIP network with only five routers may take two minutes or more to converge. RIP is a classful protocol, which means subnet masks are not advertised. This is also an unacceptable limitation in most networks. Figure 10-9 illustrates one of the most common pitfalls of using classful protocols such as RIP. Router A is advertising its directly connected network 10.10.10.0/24, but because RIP is classful, it advertises network without the subnet mask. Without a subnet mask, the receiving router must assume the entire network is included in the advertisement. Consequently, upon Specific Routing Protocols Router B believes the last update it receives Router A Router C advertises advertises 10.0.0.0 10.0.0.0 192.168.1.0/24 192.168.2.0/24 10.10.10.0/24 10.20.20.0/24 Figure 10-9. RIP classful d