There are cases when BGP neighborship between 2 BGP enabled Routers might not be working on account of incorrect BGP AS quantity configured on one of many Routers. This publish discusses one such situation.
Under is the best state of affairs the place Router R1 belongs to BGP ASN 1 whereas R2 belongs to BGP ASN 2.
Instance State of affairs: Incorrect BGP AS Quantity
Throughout configuration of units, administrator unintentionally configures an incorrect BGP AS quantity 20, as an alternative of AS 2 on R2 as proven is under diagram –
The configuration is proven under
R1
router bgp 1
internet 1.1.1.0 m 255.255.255.0
internet 192.168.12.0
neighb 192.168.12.2 remote-as 2
R2
router bgp 20 >>>>>>>>>> Incorrectly configured ASN 20 as an alternative of ASN 2
internet 2.2.2.0 m 255.255.255.0
internet 192.168.12.0
neighb 192.168.12.1 remote-as 1
When R2 is configured with fallacious AS Quantity, lets se the error message despatched by R1 and obtained by R2 –
R1 –
*Mar 1 00:27:09.287: %BGP-3-NOTIFICATION: despatched to neighbor 192.168.12.2 2/2 (peer in fallacious AS) 2 bytes 0014
R2 –
*Mar 1 00:28:37.991: %BGP-3-NOTIFICATION: obtained from neighbor 192.168.12.1 2/2 (peer in fallacious AS) 2 bytes 0014
As seen from the output logs on R1 and R2, the place R1 sends the notification and R2 receives the notification on incorrect AS quantity (proven in HEX as “0014”) which comes out to be BGP ASN “20” in decimal.
Now that we all know R2 has been wrongly configured as BGP AS 20 as an alternative of two , the administrator can carry out any of under choices to deal with the issue situation –
Possibility 1 –
Change the BGP configuration on R2 i.e. take away “Router BGP 20” and change complete configuration on “Router BGP 2”
No router bgp 20
router bgp 2
internet 2.2.2.0 m 255.255.255.0
internet 192.168.12.0
neighb 192.168.12.1 remote-as 1
Possibility 2 –
On R1 , configure neighbor command with “Distant-as” of R2 being 20 as an alternative of 2-
router bgp 1
R1(config-router)#neighbor 192.168.12.2 remote-as 20
Possibility 3 –
Configure “local-AS 2” on R2 to point out to R1 that it belongs to AS 2 and never AS 20 as under –
Router bgp 20
neighbor 192.168.12.1 local-as 2
As soon as the any of above configuration is carried out, the BGP neighborship comes up.
The output is proven under after any of the above 3 configuration is carried out on R1/R2 –
R1#sh ip bgp summ
BGP desk model is 8, important routing desk model 8
3 community entries utilizing 351 bytes of reminiscence
4 path entries utilizing 208 bytes of reminiscence
3/2 BGP path/bestpath attribute entries utilizing 372 bytes of reminiscence
1 BGP AS-PATH entries utilizing 24 bytes of reminiscence
0 BGP route-map cache entries utilizing 0 bytes of reminiscence
0 BGP filter-list cache entries utilizing 0 bytes of reminiscence
BGP utilizing 955 whole bytes of reminiscence
BGP exercise 4/1 prefixes, 6/2 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.12.2 4 2 117 117 8 0 0 00:30:02 2
R2#sh ip bgp summar
BGP desk model is 8, important routing desk model 8
3 community entries utilizing 351 bytes of reminiscence
4 path entries utilizing 208 bytes of reminiscence
3/2 BGP path/bestpath attribute entries utilizing 372 bytes of reminiscence
1 BGP AS-PATH entries utilizing 24 bytes of reminiscence
0 BGP route-map cache entries utilizing 0 bytes of reminiscence
0 BGP filter-list cache entries utilizing 0 bytes of reminiscence
BGP utilizing 955 whole bytes of reminiscence
BGP exercise 4/1 prefixes, 6/2 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.12.1 4 1 116 116 8 0 0 00:29:33 2
