Tip

Who determines policies?

People determine routing policies. You make certain choices about how you would like to route traffic between your network and other networks that you interconnect with. BGP [Border Gateway Protocol] enables you to program your routers to select paths to other networks based upon criteria that you establish before you begin BGP peering with other autonomous systems.

Suppose that you connect to the same autonomous system at two separate locations in your network. One connection is a DS3 whereas the other is a DS1. You would naturally prefer to send the majority of your traffic to your peer via the DS3 connection rather than the DS1 connection. Because BGP has no knowledge of the bandwidth of the connections in your network, you must tell the routers that you would prefer to route traffic to the networks that you learn from that peer over the DS3 rather than the DS1.

This preference, or policy, can be applied to the routes you learn from the peer on the router that the BGP peering session is configured on. Using a route-map to set the local preference, you implement your policy in your autonomous system. By setting the local preference higher on the routes that are learned from the peer on the router that the DS3 terminates on, rather than the routes learned from the peer on the router that the DS1 terminates on, you make the DS3 the preferred path to the peer.

From Cisco Router Configuration and Troubleshooting, Second Edition,

    Requires Free Membership to View

    Login

by Mark Tripod, published by New Riders, Indianapolis, Ind. For more information on Cisco Router Configuration and Troubleshooting, go to http://www.newriders.com/books/title.cfm?id=644 and http://www.informit.com/product/0735700249/.

This was first published in August 2000

Join the conversationComment

Share
Comments

    Results

    Contribute to the conversation

    All fields are required. Comments will appear at the bottom of the article.

    Disclaimer: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.

    Back to top