Les expressions régulières permettent de réaliser des filtres sur l’attribut « AS Path »
- as-path
- filter-list
- show ip bgp regexp
Dans cette exemple, le router R1 obtient la topologie suivante :
R1#show ip bgp | be Net Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 0.0.0.0 0 32768 i *> 2.0.0.0 10.1.12.2 0 0 200 i *> 3.0.0.0 10.1.12.2 0 200 300 i *> 4.0.0.0 10.1.12.2 0 200 300 400 i
Configurations :
Filtre les prefix avec l’attribut « AS Path » terminant par 300
R1# ip as-path access-list 1 deny _300$ ip as-path access-list 1 permit .* ! router bgp 100 no synchronization bgp log-neighbor-changes network 1.0.0.0 network 11.0.0.0 neighbor 10.1.12.2 remote-as 200 neighbor 10.1.12.2 filter-list 1 in no auto-summary
Vérifications
R1#show ip bgp | be Net Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 0.0.0.0 0 32768 i *> 2.0.0.0 10.1.12.2 0 0 200 i *> 4.0.0.0 10.1.12.2 0 200 300 400 i
Filtre les prefix contenant 300 dans l’attribut « AS Path »
ip as-path access-list 1 deny _300_
ip as-path access-list 1 permit .*
!
Vérifications
R1#show ip bgp | be Net
Network Next Hop Metric LocPrf Weight Path
*> 1.0.0.0 0.0.0.0 0 32768 i
*> 2.0.0.0 10.1.12.2 0 0 200 i
Filtre les prefix locaux dans les annonces
R3#show ip bgp neighbors 10.1.23.2 advertised-routes | be Net Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 10.1.23.2 0 200 100 i *> 2.0.0.0 10.1.23.2 0 0 200 i *> 3.0.0.0 0.0.0.0 0 32768 i *> 4.0.0.0 10.1.34.4 0 0 400 i
Configuration
ip as-path access-list 1 deny ^$ ip as-path access-list 1 permit .* ! router bgp 300 no synchronization bgp log-neighbor-changes network 3.0.0.0 network 33.0.0.0 neighbor 10.1.23.2 remote-as 200 neighbor 10.1.23.2 filter-list 1 out neighbor 10.1.34.4 remote-as 400 no auto-summary
Vérifications
R3#show ip bgp neighbors 10.1.23.2 advertised-routes | be Net Network Next Hop Metric LocPrf Weight Path *> 4.0.0.0 10.1.34.4 0 0 400 i Total number of prefixes 1
show ip bgp regexp
La commande « show ip bgp regexp » permet de verifier (de tester) une expression régulière avant sont implémentation
R3#show ip bgp Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 10.1.23.2 0 200 100 i *> 2.0.0.0 10.1.23.2 0 0 200 i *> 3.0.0.0 0.0.0.0 0 32768 i *> 4.0.0.0 10.1.34.4 0 0 400 i
R3#sh ip bgp regexp ^$ Network Next Hop Metric LocPrf Weight Path *> 3.0.0.0 0.0.0.0 0 32768 i
R3#sh ip bgp regexp ^200$ Network Next Hop Metric LocPrf Weight Path *> 2.0.0.0 10.1.23.2 0 0 200 i
R3#sh ip bgp regexp ^200_ Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 10.1.23.2 0 200 100 i *> 2.0.0.0 10.1.23.2 0 0 200 i
R3#sh ip bgp regexp ^[0-9]+$ Network Next Hop Metric LocPrf Weight Path *> 2.0.0.0 10.1.23.2 0 0 200 i *> 4.0.0.0 10.1.34.4 0 0 400 i
R3#sh ip bgp regexp ^200_100$ Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 10.1.23.2 0 200 100 i