There are instances when BGP neighborship between 2 BGP enabled Routers may not be working due to incorrect BGP AS number configured on one of the Routers. This post discusses one such scenario.
Below is the ideal situation where Router R1 belongs to BGP ASN 1 while R2 belongs to BGP ASN 2.
Example Scenario: Incorrect BGP AS Number
During configuration of devices, administrator accidentally configures an incorrect BGP AS number 20, instead of AS 2 on R2 as shown is below diagram –
When R2 is configured with wrongAS Number, lets se the error message sent by R1 and received by R2 –
R1 –
*Mar 1 00:27:09.287: %BGP-3-NOTIFICATION: sent to neighbor 192.168.12.2 2/2 (peer in wrong AS) 2 bytes 0014
R2 –
*Mar 1 00:28:37.991: %BGP-3-NOTIFICATION: received from neighbor 192.168.12.1 2/2 (peer in wrong AS) 2 bytes 0014
As seen from the output logs on R1 and R2, where R1 sends the notification and R2 receives the notification on incorrect AS number (shown in HEX as “0014”) which comes out to be BGP ASN “20” in decimal.
Now that we know R2 has been wrongly configured as BGP AS 20 instead of 2 , the administrator can perform any of below options to address the problem scenario –
Option 1 –
Change the BGP configuration on R2 i.e. remove “Router BGP 20” and replace whole configuration on “Router BGP 2”
R1#Config t
No router bgp 20
router bgp 2
net 2.2.2.0 m 255.255.255.0
net 192.168.12.0
neighb 192.168.12.1 remote-as 1
Option 2 –
On R1 , configure neighbor command with “Remote-as” of R2 being 20 instead of 2-
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I am a biotechnologist by qualification and a Network Enthusiast by interest. I developed interest in networking being in the company of a passionate Network Professional, my husband.
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One Response
chaithanya katari
nice one. But try to give tough troubleshoot article
nice one. But try to give tough troubleshoot article