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:
- TechRepublic: "How to use BGP to achieve Internet Redundancy"
- Internet Traffic Report
- Joe's BGP Page
- Cisco: BGP Technical Tips
- Cisco: Internetworking Technology Overview--Border Gateway Protocol (BGP)
- Cisco: Configuring BGP
- Cisco: Command Reference for BGP
- Cisco: BGP Frequently Asked Questions
- Cisco: Using Regular Expressions in BGP
- Cisco: BGP Case Studies
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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