about BGP and cost community

[ariela]

Hi guys,

when is used the cost community? When is better than local preference in the best path selection process?

Thanks for your support

Regards

Andrea

[Harold Ritter]

The BGP cost community is used among other things when you have multiple sites using EIGRP between the PE and CE and you want to force traffic to go through the MPLS VPN core despite the fact that you have a backdoor link between these sites. In this scenario, it serves a similar purpose as sham-links do for OSPF.

For more information on the above technique, please refer to the following URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a008053b5b6.html#wp1067175

By default, the cost community is evaluated after the IGP metric. The default can be changed so that the cost community is evaluated before the local-preference.

Hope this helps,

[ariela]

Thanks Harold!

Any other good practice?

Regards

Andrea

[Harold Ritter]

Andrea,

The URL I sent in my previous posting discusses a couple of situations where the cost community would be useful.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a008053b5b6.html#wp1064140

Additionally, any scenario you might think of, where the local preference needs to be overridden, would be a good place to use the cost community.

Hope this helps,