BGP Regular Expressions Cheat Sheet

BGP Regular Expressions Cheat Sheet

Regular expressions are strings of special characters that can be used to search and find character patterns. Within the scope of BGP in Cisco IOS regular expressions can be used in show commands and AS-Path access-lists to match BGP prefixes based on the information contained in their AS-Path. [boxads]

In order to understand how to build regular expressions we first need to know what the character definitions are for the regex function of IOS. The below table illustrates the regex characters and their usage. This information is contained in the Cisco IOS documentation under the Appendix of Cisco IOS Terminal Services Configuration Guide, Release 12.2.

BGP Regular Expressions Cheat Sheet:

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 ?
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BGP Regular Expressions Cheat Sheet Examples:

3-1-1, Filtering bgp output with route only origin from AS7018

Cisco Router#sh ip bgp regexp ^7018$
BGP table version is 199154652, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                 Next Hop            Metric LocPrf Weight Path
*>i3.51.92.0/23     12.122.126.39           10    100             0 7018 ?
* i                             12.122.126.39           10    100              0 7018 ?
*>i12.0.0.0/9         12.122.126.39           10    100             0 7018 i
* i                             12.122.126.39           10    100             0 7018 i
*>i12.0.0.0             12.122.126.39           10    100             0 7018 i
:

3-1-2, Filtering bgp output with route origin from AS46164

Cisco Router#sh ip bgp regexp _46164$
BGP table version is 199155849, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network            Next Hop             Metric LocPrf Weight Path
* i4.23.88.0/24  12.122.126.39           10    100        0     7018 46164 i
*>i                        12.122.126.39           10    100        0     7018 46164 i
*>i4.23.88.0/23 12.122.126.39           10    100        0    7018 46164 i
:
3-2, Filtering bgp output with route pass thru AS46164

Cisco Router#sh ip bgp regexp _6762_
BGP table version is 199165809, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network               Next Hop            Metric LocPrf Weight Path
*>i2.0.0.0/16   144.228.243.250         10    100            0 1239 6762 12654 i
* i                        144.228.243.250         10    100            0 1239 6762 12654 i
*>i2.1.0.0/21   144.228.243.250         10    100             0 1239 6762 12654 i
* i                       144.228.243.250         10    100             0 1239 6762 12654 i

3-4, Filtering bgp output with route only origin from AS1239 and directly attached with AS1239

Cisco Router#sh ip bgp regexp ^1239_[0-9]*$
BGP table version is 199175215, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                 Next Hop           Metric LocPrf Weight Path
*>i8.3.213.0/24     144.228.243.250    10       100        0 1239 4739 i
* i                             144.228.243.250    10       100        0 1239 4739 i
*>i8.10.245.0/24  144.228.243.250    10       100        0 1239 17151 i
* i                             144.228.243.250    10       100        0 1239 17151 i

 3-5, Filtering bgp output with route origin from AS46164

Cisco Router#sh ip bgp regexp ^1239$
BGP table version is 199175920, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                     Next Hop              Metric LocPrf Weight Path
*>i12.70.138.0/24   144.228.243.250         10       100          0 1239 i
* i                                144.228.243.250         10       100          0 1239 i
*>i12.195.4.0/24     144.228.243.250         10        100         0 1239 i

 3-6, Filtering bgp output with route learning from AS1239

Cisco Router#sh ip bgp regexp ^1239_
BGP table version is 199177194, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                 Next Hop            Metric LocPrf Weight Path
*>i2.0.0.0/16       144.228.243.250       10      100           0 1239 6762 12654 i
* i                          144.228.243.250        10      100           0 1239 6762 12654 i
*>i2.1.0.0/21       144.228.243.250       10      100           0 1239 6762 12654 i

 3-7, Filtering bgp output with route only direct connected ASs

Cisco Router#sh ip bgp regexp ^[0-9]+$
BGP table version is 199177786, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                  Next Hop            Metric  LocPrf Weight Path
*>i3.51.92.0/23     12.122.126.39           10    100              0  7018 ?
* i                              12.122.126.39           10    100              0  7018 ?
*>i4.0.0.0/9             4.68.185.60             10    100              0  3356 i

3-8, Filtering bgp output with route only direct connected ASN with letter 1, 7 and 4

Cisco Router#sh ip bgp regexp ^[174]+$
BGP table version is 199179097, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network          Next Hop                Metric LocPrf Weight Path
*>i24.238.0.0/24    154.54.13.137      10       100          0 174 i
* i                               154.54.13.137       10      100          0 174 i
*>i24.238.2.0/24    154.54.13.137       10      100          0 714 i
* i                               154.54.13.137       10      100          0 714 i
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3-9, Filtering bgp output with route origin from AS46164 and thru AS7018

Cisco Router#sh ip bgp reg ^7018_46164$
BGP table version is 199190289, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                Next Hop         Metric LocPrf Weight Path
* i4.23.88.0/24     12.122.126.39       10     100         0   7018 46164 i
*>i                           12.122.126.39       10    100          0   7018 46164 i
*>i4.23.88.0/23   12.122.126.39        10    100          0   7018 46164 i
* i                            12.122.126.39       10    100          0   7018 46164 i

 3-10, Filtering bgp output with route locally origin

Cisco Router#sh ip bgp reg ^$
BGP table version is 199192287, local router ID is x.x.x.x
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale
Origin codes: i – IGP, e – EGP, ? – incomplete

Network                 Next Hop                  Metric LocPrf Weight Path
*>i4.68.62.96/30    140.222.130.48                      100           0 i
* i                               140.222.130.48                      100           0 i
*>i4.68.63.140/30  140.222.130.48                      100           0 i
* i                               140.222.130.48                      100           0 i

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