eng-mssk: June 2015

We are going to use the above topology to demonstrate some regular expressions examples using Cisco IOS software

Configurations

Each router will be configured with two loopback interfaces that will be advertised into BGP, all BGP relations are eBGP

interface Loopback1

ip address 192.168.1.1 255.255.255.0

interface Loopback2

ip address 172.16.1.1 255.255.255.0

interface FastEthernet0/0

ip address 192.168.12.1 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet0/1

ip address 192.168.13.1 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet1/0

ip address 192.168.14.1 255.255.255.0

speed 100

full-duplex

no shut

router bgp 9038

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 192.168.12.2 remote-as 3356

neighbor 192.168.13.3 remote-as 47887

neighbor 192.168.14.4 remote-as 44666

address-family ipv4

neighbor 192.168.12.2 activate

neighbor 192.168.13.3 activate

neighbor 192.168.14.4 activate

no auto-summary

no synchronization

network 172.16.1.0 mask 255.255.255.0

network 192.168.1.0

exit-address-family

interface Loopback1

ip address 192.168.2.2 255.255.255.0

interface Loopback2

ip address 172.16.2.2 255.255.255.0

interface FastEthernet0/0

ip address 192.168.12.2 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet0/1

ip address 192.168.25.2 255.255.255.0

speed 100

full-duplex

no shut

router bgp 3356

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 192.168.12.1 remote-as 9038

neighbor 192.168.25.5 remote-as 8966

address-family ipv4

neighbor 192.168.12.1 activate

neighbor 192.168.25.5 activate

no auto-summary

no synchronization

network 172.16.2.0 mask 255.255.255.0

network 192.168.2.0

exit-address-family

interface Loopback1

ip address 192.168.3.3 255.255.255.0

interface Loopback2

ip address 172.16.3.3 255.255.255.0

interface FastEthernet0/0

ip address 192.168.13.3 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet0/1

ip address 192.168.35.3 255.255.255.0

speed 100

full-duplex

no shut

router bgp 47887

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 192.168.13.1 remote-as 9038

neighbor 192.168.35.5 remote-as 8966

address-family ipv4

neighbor 192.168.13.1 activate

neighbor 192.168.35.5 activate

no auto-summary

no synchronization

network 172.16.3.0 mask 255.255.255.0

network 192.168.3.0

exit-address-family

interface Loopback1

ip address 192.168.4.4 255.255.255.0

interface Loopback2

ip address 172.16.4.4 255.255.255.0

interface FastEthernet0/0

ip address 192.168.14.4 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet0/1

ip address 192.168.46.4 255.255.255.0

speed 100

full-duplex

no shut

router bgp 44666

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 192.168.14.1 remote-as 9038

neighbor 192.168.46.6 remote-as 7922

address-family ipv4

neighbor 192.168.14.1 activate

neighbor 192.168.46.6 activate

no auto-summary

no synchronization

network 172.16.4.0 mask 255.255.255.0

network 192.168.4.0

exit-address-family

interface Loopback1

ip address 192.168.5.5 255.255.255.0

interface Loopback2

ip address 172.16.5.5 255.255.255.0

interface FastEthernet0/0

ip address 192.168.25.5 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet0/1

ip address 192.168.56.5 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet1/0

ip address 192.168.35.5 255.255.255.0

speed 100

full-duplex

no shut

router bgp 8966

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 192.168.25.2 remote-as 3356

neighbor 192.168.35.3 remote-as 47887

neighbor 192.168.56.6 remote-as 7922

address-family ipv4

neighbor 192.168.25.2 activate

neighbor 192.168.35.3 activate

neighbor 192.168.56.6 activate

no auto-summary

no synchronization

network 172.16.5.0 mask 255.255.255.0

network 192.168.5.0

exit-address-family

interface Loopback1

ip address 192.168.6.6 255.255.255.0

interface Loopback2

ip address 172.16.6.6 255.255.255.0

interface FastEthernet0/0

ip address 192.168.56.6 255.255.255.0

speed 100

full-duplex

no shut

interface FastEthernet0/1

ip address 192.168.46.6 255.255.255.0

speed 100

full-duplex

no shut

router bgp 7922

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 192.168.46.4 remote-as 44666

neighbor 192.168.56.5 remote-as 8966

address-family ipv4

neighbor 192.168.46.4 activate

neighbor 192.168.56.5 activate

no auto-summary

no synchronization

network 172.16.6.0 mask 255.255.255.0

network 192.168.6.0

exit-address-family

Characters

Below is the characters used in the BGP regular expressions configuration

?	repeats the previous character one or zero times.
*	repeats the previous character zero or many times.
+	repeats the previous character one or more times.
^	matches the beginning of a string.
$	matches the end of a string.
[]	is a range.
_	matches the space between AS numbers or the end of the AS PATH list.
\\	is an escape character. You’ll need this for BGP confederations.

Outputs

Before we start manipulating with regular expressions, let us check the BGP table on R1

R1#sh ip bgp

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.1.0/24 0.0.0.0 0 32768 i

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

*> 172.16.4.0/24 192.168.14.4 0 0 44666 i

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

*> 172.16.6.0/24 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

*> 192.168.1.0 0.0.0.0 0 32768 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

*> 192.168.4.0 192.168.14.4 0 0 44666 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

Network Next Hop Metric LocPrf Weight Path

*> 192.168.6.0 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

As well, let us dive deeply in the output above as a review for the BGP attributes and best path selection criteria

The prefixes 192.168.1.0 and 172.16.1.0/24 have a next-hop value of 0.0.0.0, which means that these prefixes were locally originated (either using network or redistribution), the 172.16.1.0 appears attached with its subnet mask because it’s a class B prefix and we configured the mask to be /24 in the network statement, 192.168.1.0 is already class C prefix and we did not change the classful boundary, as well, the as-path is empty because again these prefixes are locally originated

Let us check now the prefix 172.16.5.0/24 , it has been learned through three different paths , as we did not manipulate any attributes , the as-path will play a role according to the selection criteria , so the path 44666 7922 8966 will be discarded compared to the other two paths which are shorter , the tie will be between the 47887 8966 and 3356 8966 which are equal in the as-path and both are eBGP , so going down the list , the oldest one learned will be installed in the RIB (routing table)

Regular Expressions Examples

Locally Originated Routes

As mentioned above, the locally originated routes have a next-hop value of 0.0.0.0 and can be shown using the regular expression of ^$

R1#sh ip bgp regexp ^$

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.1.0/24 0.0.0.0 0 32768 i

*> 192.168.1.0 0.0.0.0 0 32768 i

R2#sh ip bgp regexp ^$

BGP table version is 13, local router ID is 192.168.2.2

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

*> 172.16.2.0/24 0.0.0.0 0 32768 i

*> 192.168.2.0 0.0.0.0 0 32768 i

R3#sh ip bgp regexp ^$

BGP table version is 13, local router ID is 192.168.3.3

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

*> 172.16.3.0/24 0.0.0.0 0 32768 i

*> 192.168.3.0 0.0.0.0 0 32768 i

R4#sh ip bgp regexp ^$

BGP table version is 15, local router ID is 192.168.4.4

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

*> 172.16.4.0/24 0.0.0.0 0 32768 i

*> 192.168.4.0 0.0.0.0 0 32768 i

R5#sh ip bgp regexp ^$

BGP table version is 15, local router ID is 192.168.5.5

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

*> 172.16.5.0/24 0.0.0.0 0 32768 i

*> 192.168.5.0 0.0.0.0 0 32768 i

R6#sh ip bgp regexp ^$

BGP table version is 13, local router ID is 192.168.6.6

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

*> 172.16.6.0/24 0.0.0.0 0 32768 i

*> 192.168.6.0 0.0.0.0 0 32768 i

Anything to Match

This will match any route, i.e. it will show the BGP table

R1#sh ip bgp regexp .*

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.1.0/24 0.0.0.0 0 32768 i

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

*> 172.16.4.0/24 192.168.14.4 0 0 44666 i

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

*> 172.16.6.0/24 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

*> 192.168.1.0 0.0.0.0 0 32768 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

*> 192.168.4.0 192.168.14.4 0 0 44666 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

Network Next Hop Metric LocPrf Weight Path

*> 192.168.6.0 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

Routes originated in a specific AS

To check routes originated in a specific AS #, we will be using the pattern _AS#$

R1#sh ip bgp regexp _3356$

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

R1#sh ip bgp regexp _47887$

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

R1#sh ip bgp regexp _44666$

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.4.0/24 192.168.14.4 0 0 44666 i

*> 192.168.4.0 192.168.14.4 0 0 44666 i

R1#sh ip bgp regexp _8966$

BGP table version is 15, local router ID is 192.168.14.1

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

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

R1#sh ip bgp regexp _7922$

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.6.0/24 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

*> 192.168.6.0 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

Routes learned from specific AS (the AS-PATH starts with that AS)

To match these kind of routes we will using the regular expression ^AS_

R1#sh ip bgp regexp .*

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.1.0/24 0.0.0.0 0 32768 i

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

*> 172.16.4.0/24 192.168.14.4 0 0 44666 i

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

*> 172.16.6.0/24 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

*> 192.168.1.0 0.0.0.0 0 32768 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

*> 192.168.4.0 192.168.14.4 0 0 44666 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

Network Next Hop Metric LocPrf Weight Path

*> 192.168.6.0 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

R1#sh ip bgp regexp ^3356_

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 172.16.5.0/24 192.168.12.2 0 3356 8966 i

* 172.16.6.0/24 192.168.12.2 0 3356 8966 7922 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

*> 192.168.5.0 192.168.12.2 0 3356 8966 i

* 192.168.6.0 192.168.12.2 0 3356 8966 7922 i

R1#sh ip bgp regexp ^47887_

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

* 172.16.5.0/24 192.168.13.3 0 47887 8966 i

* 172.16.6.0/24 192.168.13.3 0 47887 8966 7922 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

* 192.168.5.0 192.168.13.3 0 47887 8966 i

* 192.168.6.0 192.168.13.3 0 47887 8966 7922 i

Match any instance of a specific AS (from or through)

To match these kinds of routes we will be using the pattern _AS_

R1#sh ip bgp regexp _3356_

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 172.16.5.0/24 192.168.12.2 0 3356 8966 i

* 172.16.6.0/24 192.168.12.2 0 3356 8966 7922 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

*> 192.168.5.0 192.168.12.2 0 3356 8966 i

* 192.168.6.0 192.168.12.2 0 3356 8966 7922 i

R1#sh ip bgp regexp _47887_

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

* 172.16.5.0/24 192.168.13.3 0 47887 8966 i

* 172.16.6.0/24 192.168.13.3 0 47887 8966 7922 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

* 192.168.5.0 192.168.13.3 0 47887 8966 i

* 192.168.6.0 192.168.13.3 0 47887 8966 7922 i

R1#sh ip bgp regexp _44666_

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.4.0/24 192.168.14.4 0 0 44666 i

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

*> 172.16.6.0/24 192.168.14.4 0 44666 7922 i

*> 192.168.4.0 192.168.14.4 0 0 44666 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

*> 192.168.6.0 192.168.14.4 0 44666 7922 i

R1#sh ip bgp regexp _8966_

BGP table version is 15, local router ID is 192.168.14.1

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

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

* 172.16.6.0/24 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

* 192.168.13.3 0 47887 8966 i

*> 192.168.12.2 0 3356 8966 i

* 192.168.6.0 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

R1#sh ip bgp regexp _7922_

BGP table version is 15, local router ID is 192.168.14.1

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

* 172.16.5.0/24 192.168.14.4 0 44666 7922 8966 i

*> 172.16.6.0/24 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

* 192.168.5.0 192.168.14.4 0 44666 7922 8966 i

*> 192.168.6.0 192.168.14.4 0 44666 7922 i

* 192.168.13.3 0 47887 8966 7922 i

* 192.168.12.2 0 3356 8966 7922 i

Routes learned from my directly connected ASes

As can be seen from the topology, AS# 9038 has three directly connected ASes, we will be using the expression ^[0-9]+$ to match these routes

R1#sh ip bgp summary

BGP router identifier 192.168.14.1, local AS number 9038

BGP table version is 15, main routing table version 15

12 network entries using 1440 bytes of memory

20 path entries using 1040 bytes of memory

11/6 BGP path/bestpath attribute entries using 1364 bytes of memory

9 BGP AS-PATH entries using 216 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

Bitfield cache entries: current 1 (at peak 1) using 32 bytes of memory

BGP using 4092 total bytes of memory

BGP activity 12/0 prefixes, 20/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

192.168.12.2 4 3356 40 41 15 0 0 00:31:25 6

192.168.13.3 4 47887 39 40 15 0 0 00:29:33 6

192.168.14.4 4 44666 38 38 15 0 0 00:27:34 6

R1#sh ip bgp regexp ^[0-9]+$

BGP table version is 15, local router ID is 192.168.14.1

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

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

*> 172.16.4.0/24 192.168.14.4 0 0 44666 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

*> 192.168.4.0 192.168.14.4 0 0 44666 i

Quote-regexp

If we wanted to filter the output more , we can use quote-regexp instead , for example if we wanted to show all routes originated in AS #9038 that starts with 192 , we can use the below command

R3#sh ip bgp quote-regexp "_9038$" | include ^. 192\.

* 192.168.1.0 192.168.35.5 0 8966 3356 9038 i

R3#sh ip bgp quote-regexp "_9038$" | include ^. 172\.

* 172.16.1.0/24 192.168.35.5 0 8966 3356 9038 i

R5#sh ip bgp quote-regexp "_9038$" | include ^. 192\.

* 192.168.1.0 192.168.56.6 0 7922 44666 9038 i

R5#sh ip bgp quote-regexp "_9038$" | include ^. 172\.

* 172.16.1.0/24 192.168.56.6 0 7922 44666 9038 i

Brackets

The below output will match routes from AS that start with 4, 5, 6, 7 or 8 and have 6 more 6s in the as-path

R2#sh ip bgp regexp [4-8]6+$

BGP table version is 13, local router ID is 192.168.2.2

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

* 172.16.4.0/24 192.168.25.5 0 8966 7922 44666 i

*> 192.168.12.1 0 9038 44666 i

* 172.16.5.0/24 192.168.12.1 0 9038 47887 8966 i

*> 192.168.25.5 0 0 8966 i

* 192.168.4.0 192.168.25.5 0 8966 7922 44666 i

*> 192.168.12.1 0 9038 44666 i

* 192.168.5.0 192.168.12.1 0 9038 47887 8966 i

*> 192.168.25.5 0 0 8966 i

R3#sh ip bgp regexp _3*[5-6]+[1-9]$

BGP table version is 13, local router ID is 192.168.3.3

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

* 172.16.2.0/24 192.168.35.5 0 8966 3356 i

*> 192.168.13.1 0 9038 3356 i

* 192.168.2.0 192.168.35.5 0 8966 3356 i

*> 192.168.13.1 0 9038 3356 i

. matches any character, so we if we applied the output below, we can see that 9 will be matched as the rest of the command contains 038

R3#sh ip bgp regexp ^.038

BGP table version is 13, local router ID is 192.168.3.3

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

*> 172.16.1.0/24 192.168.13.1 0 0 9038 i

*> 172.16.2.0/24 192.168.13.1 0 9038 3356 i

*> 172.16.4.0/24 192.168.13.1 0 9038 44666 i

* 172.16.6.0/24 192.168.13.1 0 9038 44666 7922 i

*> 192.168.1.0 192.168.13.1 0 0 9038 i

*> 192.168.2.0 192.168.13.1 0 9038 3356 i

*> 192.168.4.0 192.168.13.1 0 9038 44666 i

* 192.168.6.0 192.168.13.1 0 9038 44666 7922 i

The below matches the routes from my directly connected neighbors, but not all neighbors only 3356

R1#sh ip bgp regexp ^[3356]+$

BGP table version is 15, local router ID is 192.168.1.1

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

*> 172.16.2.0/24 192.168.12.2 0 0 3356 i

*> 192.168.2.0 192.168.12.2 0 0 3356 i

The below matches the routes that starts from 3356 and passes through the direct AS 8966 (following each other in the as-path)

R1#show ip bgp regexp ^3356_8966$

BGP table version is 15, local router ID is 192.168.1.1

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

* 172.16.5.0/24 192.168.12.2 0 3356 8966 i

* 192.168.5.0 192.168.12.2 0 3356 8966 i

Filtering

We can use regular expressions to filter routes and modify attributes instead of matching the same prefixes

Let us change the local preference value for a specific routes matched based on a specific regular expression

R2#sh ip bgp

BGP table version is 13, local router ID is 192.168.2.2

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

*> 172.16.1.0/24 192.168.12.1 0 0 9038 i

*> 172.16.2.0/24 0.0.0.0 0 32768 i

* 172.16.3.0/24 192.168.25.5 0 8966 47887 i

*> 192.168.12.1 0 9038 47887 i

* 172.16.4.0/24 192.168.25.5 0 8966 7922 44666 i

*> 192.168.12.1 0 9038 44666 i

* 172.16.5.0/24 192.168.12.1 0 9038 47887 8966 i

*> 192.168.25.5 0 0 8966 i

* 172.16.6.0/24 192.168.12.1 0 9038 44666 7922 i

*> 192.168.25.5 0 8966 7922 i

*> 192.168.1.0 192.168.12.1 0 0 9038 i

*> 192.168.2.0 0.0.0.0 0 32768 i

* 192.168.3.0 192.168.25.5 0 8966 47887 i

*> 192.168.12.1 0 9038 47887 i

* 192.168.4.0 192.168.25.5 0 8966 7922 44666 i

*> 192.168.12.1 0 9038 44666 i

* 192.168.5.0 192.168.12.1 0 9038 47887 8966 i

Network Next Hop Metric LocPrf Weight Path

*> 192.168.25.5 0 0 8966 i

* 192.168.6.0 192.168.12.1 0 9038 44666 7922 i

*> 192.168.25.5 0 8966 7922 i

ip as-path access-list 10 permit ^9038_44666$

route-map LP permit 10

match as-path 10

set local-preference 300

route-map LP permit 20

router bgp 3356

address-family ipv4 unicast

neighbor 192.168.12.1 route-map LP in

R2#sho ip bgp regexp ^9038_44666$

BGP table version is 15, local router ID is 192.168.2.2

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

*> 172.16.4.0/24 192.168.12.1 300 0 9038 44666 i

*> 192.168.4.0 192.168.12.1 300 0 9038 44666 i

Now, let us try to change the origin code for specific routes matched based on a specific regular expression

R1#sh ip bgp regexp _47887$

BGP table version is 15, local router ID is 192.168.1.1

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

*> 172.16.3.0/24 192.168.13.3 0 0 47887 i

*> 192.168.3.0 192.168.13.3 0 0 47887 i

ip as-path access-list 14 permit _47887$

route-map ORIGIN permit 10

match as-path 14

set origin incomplete

route-map ORIGIN permit 20

router bgp 9038

address-family ipv4 unicast

neighbor 192.168.13.3 route-map ORIGIN in

R1#sh ip bgp regexp _47887$

BGP table version is 17, local router ID is 192.168.1.1

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

*> 172.16.3.0/24 192.168.13.3 0 0 47887 ?

*> 192.168.3.0 192.168.13.3 0 0 47887 ?

IOS vs IOS XR

As we know, the syntax is somehow different between the IOS and IOS XR, we will go the same examples we listed above and convert them to IOS XR syntax

IOS Command	IOS XR Command
show ip bgp regexp {Regular-Expression)	show bgp regexp {Regular-Expression}
ip as-path access-list 10 permit ^9038_44666$	as-path-set SET1 ios-regex '^9038_44666$' end-set
ip as-path access-list 11 permit _9038$	as-path-set SET2 ios-regex '_9038$' end-set or as-path-set SET2 originates-from '9038' end-set
ip as-path access-list 12 permit _3356_	as-path-set SET3 ios-regex '_3356_' end-set or as-path-set SET2 passes-through '3356' end-set
ip as-path access-list 14 permit _47887$ route-map ORIGIN permit 10 match as-path 14 set origin incomplete route-map ORIGIN permit 20 router bgp 9038 address-family ipv4 unicast neighbor 192.168.13.3 route-map ORIGIN in	as-path-set SET4 ios-regex '_47887$' end-set route-policy ORIGIN if as-path in SET4 then set origin incomplete else pass endif end-policy router bgp 9038 neighbor 192.168.13.3 address-family ipv4 unicast route-policy ORIGIN in
ip as-path access-list 10 permit ^9038_44666$ route-map LP permit 10 match as-path 10 set local-preference 300 route-map LP permit 20 router bgp 3356 address-family ipv4 unicast neighbor 192.168.12.1 route-map LP in	as-path-set SET5 ios-regex '^9038_44666$' end-set route-policy LP if as-path in SET5 then set local-preference 300 else pass endif end-policy router bgp 9038 neighbor 192.168.12.1 address-family ipv4 unicast route-policy LP in

eng-mssk

Monday, June 8, 2015

BGP Regular Expressions

Brackets

Contributors