You want to summarize the incoming routing information to reduce the size of your routing table.
One of the easiest ways to reduce your routing table size is to filter out most of the external routes and replace them with a default. To do this, you first create a static default route pointing to some known remote network. If this remote network is up, then you can safely assume that your ISP is working properly. Then you simply filter out all of the remaining uninteresting routes:
configure terminalEnter configuration commands, one per line. End with CNTL/Z. Router1(config)#
0.0.0.0 0.0.0.0 192.168.101.0 1
0.0.0.0 0.0.0.0 192.168.102.0 2
For most typical Internet connections, you will need to drastically reduce the amount of routing information that you receive. A typical Internet backbone router needs to support BGP routes for well over 100,000 prefixes. So unless you are operating the ISP and need to support a large fraction of the public address space, it is a good idea to cut out as much as possible. ...