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 ..

MPLS Traffic Engineering with Autoroute

This recipe uses Cisco's Autoroute feature for managing Traffic Engineering (TE) with OSPF in an MPLS network. For this method, we must explicitly define all of the traffic paths and associate them with Tunnels on the PE routers: Router-PE1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router-PE1(config)#mpls traffic-eng tunnels Router-PE1(config)#interface Loopback0 Router-PE1(config-if)#ip address 10.0.0.2 255.255.255.255 Router..

Removing Private ASNs from the AS Path

You have to be extremely careful that any unregistered ASNs that you may be using don't propagate into the public Internet. In this example, the router has a BGP connection to an ISP, which uses ASN 1. Our router uses ASN 2 and connects to another router with an unregistered ASN, 65500: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#interface Serial0 Router1(config-if)#description connection to ISP #1, ASN 1 Rou..