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Route Summarization for BGP
that the more specific routes have passed through. The command and the
syntaxes are as follows:
ip-address mask [summary-only]
Let's take a look at a sample configuration using this command:
RouterA(config)#router bgp 65000
RouterA(config-router)#network mask
RouterA(config-router)#neighbor remote-as 64500
RouterA(config-router)#neighbor remote-as
RouterA(config-router)#network mask
RouterA(config-router)#network mask
RouterA(config-router)#no synchronization
RouterA(config-router)#neighbor next-hop-self
RouterA(config-router)#aggregate-address summary-only
Advertising Networks into BGP
Redistribution of routing information occurs in a number of ways. The pri-
mary way is the network command, which was discussed in Chapters 8, "Con-
figuring Basic BGP" and 9, "BGP Scalability and Advanced Features." The
command allows BGP to advertise a network that is already in the
IP table. When using the network command, you must identify all the net-
works in the AS that you want to advertise.
You can also use the ip route command to create a static route. The
static route is then redistributed into BGP. Redistribution occurs when a
router uses different protocols to advertise routing information received
between the protocols. BGP considers a static route to be a protocol. Static
route information is advertised to BGP.
The third way to create a static route is to redistribute dynamically learned
routes (routes learned through an IGP) into BGP. In Chapter 8 we learned the
commands to enable this; however, Cisco does not recommend this
approach because of convergence issues and the possibility of introducing
routing loops into the network. Convergence is the time it takes for the net-
work to recover from a change in the network's topology.
Copyright ©2001 SYBEX , Inc., Alameda, CA