Basic Cisco BGP Configuration

If you are setting up BGP for the first time, or just want a quick reminder of the rudimentary configuration, you might find this sample config of some help.

This example is based on a fictional network with:

BGP block:

router bgp 12345 This starts my BGP config block.
 no synchronization Do not tie my BGP announcements to OSPF, RIP,
or other routing protocol.
 redistribute static Announce my static routes
 network 223.100.32.0 mask 255.255.224.0 Announce my /19 network block
 network 223.200.8.0 mask 255.255.248.0 Announce my /21 network block
 aggregate-address 223.100.32.0 255.255.224.0 Announce my /19 block as a single entity
 aggregate-address 223.200.8.0 255.255.224.0 Announce my /21 block as a single entity
 neighbor 160.123.123.1 remote-as 1234 My first BGP peer is AS 1234
 neighbor 160.123.123.1 distribute-list 1 in See access-list 1 for description.
 neighbor 160.123.123.1 filter-list 10 out Only announce my own routes
 neighbor 206.150.180.5 remote-as 5678 My second BGP peer is AS 5678
 neighbor 206.150.180.5 distribute-list 1 in See access-list 1 for description.
 neighbor 206.150.180.5 filter-list 10 out Only announce my own routes
 no auto-summary Do not combine small routes into larger ones.

Filter rules:

ip as-path access-list 10 permit ^$ Only announce routes that I originate.
access-list 1 deny 223.100.32.0 0.0.31.255
access-list 1 deny 223.200.8.0 0.0.7.255
access-list 1 permit any		 If my BGP peer sends me one of my own routes, discard it.

Static routes:

ip route 223.100.32.0 255.255.224.0 null0 Even if one (or more) blocks in my /19 do not have a route,
continue routing the whole /19
ip route 223.200.8.0 255.255.248.0 null0 Always advertise the full /21
Are you looking into using a Linux or BSD box as a router? Quagga is routing protocol software that looks and acts like Cisco IOS, but runs on your favorite operating system and is free.
More info here: Quagga project (formerly "Zebra")

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