Server platforms Toolkit

Use IP and BGP to troubleshoot Internet connectivity

David Davis Tech Republic

Published: 24 Jun 2003 15:35 BST

As you can see, this router has 52 paths to get to the BGP AS where my IP address is located. It says that path #26 is the best route (based on BGP metrics). You can also do a BGP regular expression, with AS numbers, like this one:
show ip bgp regexp 23215$

This regular expression asks for every IP network in BGP that terminates at AS 23215. I won't include the full output since it is hundreds of lines long, but Listing B is a truncated look at the output.

Basically, this router has hundreds of networks that terminate at the AS number given. This command may be useful for troubleshooting BGP paths, especially if your AS is advertising fewer routes. For explanations of what each command does, refer to Configuring BGP and the Command Reference for BGP on Cisco's Web site. For more information on how BGP works, configuring BGP, and doing BGP show commands, check out these links:

Lower the frustration level
Because the Internet is the most complex network in the world and is run by thousands of providers, getting problems resolved can be frustrating and time consuming. The next time you need some Internet troubleshooting tools, you may be able to use these examples and tips to pinpoint the problem and get it resolved faster. Or perhaps tell your ISP where the problem is so that it can be resolved faster.

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