Using Regular Expressions to Match AS_PATH

A Cisco IOS AS_PATH filter has one or more configured lines, with each line requiring a regex. The logic is then applied as follows: 1. The regex of the first line in the list is applied to the AS_PATH of each route. 2. For matched NLRI, the NLRI is passed or filtered based on that AS_PATH filter’s configured permit or deny action. 3. For unmatched NLRI, Steps 1 and 2 are repeated, using the next line in the AS_PATH filter, analyzing all NLRI yet to be matched by this ..

Differentiated Packet Servicing

Conventional IP packet forwarding uses only the IP destination address contained within the Layer 3 header within a packet to make a forwarding decision. The hop-by-hop destination-only paradigm used today prevents a number of innovative approaches to network design and traffic flow optimization. In Figure C-2, for example, the direct link between the San Francisco core router and the Washington core router forwards the traffic entering the network in any of the Bay Area Poin..

Using SNMP to Copy a New IOS Image

Before you can upload or download the router's IOS image to a TFTP server, you have to set up a valid read-write SNMP community string: Router#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router(config)#snmp-server community ORARW rw Router(config)#end Then you can download a copy of your router's current IOS file to your TFTP server with the following Unix commands: Freebsd% touch /tftpboot/c2600-jk9o3s-mz.122-7a.bin Freebsd% chmod ..

Creating Exception Dump Files

This is the one recipe in this book that we hope none of our readers ever need to use. The main reason for creating an exception dump of your router memory contents is to help Cisco's TAC in diagnosing catastrophic software problems with one of your routers. When you have these types of extreme problems, however, the TAC will often ask to do an exception dump on the router. So we have included this recipe so that you'll know what to do if it ever becomes necessary. An excepti..

Using Committed Access Rate

Committed Access Rate (CAR) provides a useful method for policing the traffic rate through an interface. The main features of CAR are functionally similar to traffic shaping, but it also allows several extremely useful extensions. This first example shows the simplest application. We have configured CAR here to do basic rate limiting. The interface will transmit packets at an average rate of 500,000 bps, allowing bursts of 4500 bytes. If there is a burst of longer than 9000 b..