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Extracting BGP info with regular expressions
By stretch | Saturday, May 10, 2008 at 11:54 a.m. UTC
A reader recently asked for some handy regular expressions for extracting useful information from BGP tables and outputs. Following are a few that I came up with. If you have any more please send them in or leave a comment!
To find all subnets originating from AS 100 (AS path ends with 100):
Router# show ip bgp regexp _100$ ... Network Next Hop Metric LocPrf Weight Path * 10.1.0.0/30 172.16.0.6 0 300 100 ? *> 172.16.0.1 0 0 100 ? * 172.16.0.0/30 172.16.0.6 0 300 100 ? * 172.16.0.1 0 0 100 ? ...
To find all subnets reachable via AS 100 (AS path begins with 100):
Router# show ip bgp regexp ^100_ ... Network Next Hop Metric LocPrf Weight Path *> 10.1.0.0/30 172.16.0.1 0 0 100 ? * 10.3.0.0/30 172.16.0.1 0 100 300 ? * 172.16.0.0/30 172.16.0.1 0 0 100 ? *> 172.16.0.8/30 172.16.0.1 0 0 100 ? ...
To find all routes traversing AS 100:
Router# show ip bgp regexp _100_ ... Network Next Hop Metric LocPrf Weight Path * 10.1.0.0/30 172.16.0.6 0 300 100 ? *> 172.16.0.1 0 0 100 ? * 10.3.0.0/30 172.16.0.1 0 100 300 ? * 172.16.0.0/30 172.16.0.6 0 300 100 ? ...
If you need to further filter the output, use quote-regexp instead. For example, to find all 172.x.x.x routes originating from AS 100:
Router# show ip bgp quote-regexp "_100$" | include ^. 172\. * 172.16.0.0/30 172.16.0.6 0 300 100 ? * 172.31.0.1/32 172.16.0.6 0 300 100 ?
Or, to find all subnets currently being reached via AS 100:
Router# show ip bgp quote-regexp "^100_" | i ^.> *> 10.1.0.0/30 172.16.0.1 0 0 100 ? *> 172.16.0.8/30 172.16.0.1 0 0 100 ? *> 172.31.0.1/32 172.16.0.1 0 0 100 ?
Unfortunately, Cisco's implementation of regular expressions is rather crippled. For (much) more advanced functionality, consider using Tcl scripting.
Posted in Tips and Tricks
Comments
May 10, 2011 at 5:33 p.m. UTC
جرمی، این ها دیگه چیه مینویسی؟ قبلا ها چیزای باحال تری می نوشتی. دمت گرم
May 6, 2012 at 12:38 p.m. UTC
excellent cheers
August 31, 2012 at 11:51 a.m. UTC
thank you
September 12, 2012 at 5:03 a.m. UTC
Hi Jeremy,
Please explain me how to find AS number two AS away from my AS.
ex: my AS is 17443, my next AS 47125, how to find next AS after that. Please explain me in regular expression.
Thank you.
July 6, 2015 at 3:09 a.m. UTC
This article is greate! I was confused about the regexp and quote-regexp. Now its much more clear to me. Thank you!
April 19, 2016 at 6:06 p.m. UTC
great article
May 31, 2016 at 7:49 p.m. UTC
quote-regexp? You just blew my mind.