3.7.d Implement optimize and troubleshoot routing policies

3.7.d [iv] Communities, extended communities

file this under stupid-bgp-tricks…

from cisco.com

The link bandwidth extended community attribute is a 4-byte value that is configured for a link on the demilitarized zone (DMZ) interface that connects two single hop eBGP peers. The link bandwidth extended community attribute is used as a traffic sharing value relative to other paths while traffic is being forwarded. Two paths are designated as equal for load balancing if the weight, local-pref, as-path length, Multi Exit Discriminator (MED), and Interior Gateway Protocol (IGP) costs are the same.

r1#sh ip bgp 192.168.45.5
BGP routing table entry for 192.168.45.0/24, version 9
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Multipath: iBGP
Not advertised to any peer
2
192.168.35.5 (metric 11) from 3.3.3.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, valid, internal
DMZ-Link Bw 1250 kbytes
2
192.168.24.4 (metric 2) from 2.2.2.2 (2.2.2.2)
Origin IGP, metric 0, localpref 100, valid, internal, best
DMZ-Link Bw 12500 kbytes

rene has a great lab on this here:

http://gns3vault.com/BGP/bgp-dmz-link-bandwidth.html

ine has shit on this here:

http://blog.ine.com/2010/04/06/move-over-variance-bgp-proportional-load-balancing-is-here/