BGP Path Selection Manipulation Issues!

[san ju.]

Hello All,

I'm a beginner in BGP and I'm experiencing an issue. I have two CSR1000v routers, R1 and R2, both connected to a single link provided by my ISP, which is divided into two VLANs, 1040 and 1041. Currently, both BGP sessions are up, and initially, the IN and OUT traffic was going through R1. However, I wanted to change the traffic to flow through R2, and monitored this change using my SNMP monitor, and I observed that the outgoing traffic (BGP-OUT) correctly switched to R2. But the incoming traffic (BGP-IN) did not follow suit, it continued to go through R1. I made the following configuration changes on my router, but the issue persisted.

R1
router bgp 376786
neighbor 175.32.118.12 remote-as 60849
!
neighbor 175.32.118.12 activate
neighbor 175.32.118.12 next-hop-self
neighbor 175.32.118.12 soft-reconfiguration inbound
neighbor 175.32.118.12 route-map ebgpin in
neighbor 175.32.118.12 route-map ebgpout out
exit-address-family
!
route-map ebgpin permit 10
match ip address prefix-list defaultv4
!
route-map ebgpout permit 10
match ip address prefix-list v4-bgp-filter-ixp
set as-path prepend 376786 376786 376786
!
ip prefix-list defaultv4 seq 10 permit 0.0.0.0/0
!
ip prefix-list v4-bgp-filter-ixp seq 5 permit 23.158.4.0/24
ip prefix-list v4-bgp-filter-ixp seq 10 permit 23.182.103.0/24
ip prefix-list v4-bgp-filter-ixp seq 50 deny 0.0.0.0/0

R2
router bgp 61273
 neighbor 175.32.118.16 remote-as 60849
 !
 address-family ipv4
  neighbor 175.32.118.16 activate
  neighbor 175.32.118.16 next-hop-self
  neighbor 175.32.118.16 soft-reconfiguration inbound
  neighbor 175.32.118.16 route-map ebgpin in
  neighbor 175.32.118.16 route-map ebgpout out
 !
route-map ebgpin permit 10 
 match ip address prefix-list defaultv4
 set local-preference 200
!
route-map ebgpout permit 10 
 match ip address prefix-list v4-bgp-filter-ixp
!
ip prefix-list defaultv4 seq 10 permit 0.0.0.0/0
!
ip prefix-list v4-bgp-filter-ixp seq 5 permit 23.158.4.0/24
ip prefix-list v4-bgp-filter-ixp seq 10 permit 23.182.103.0/24
ip prefix-list v4-bgp-filter-ixp seq 50 deny 0.0.0.0/0

Note: R1 is in AS 376786, and R2 is in AS 61273. Both router has eBGP using LAN IPs

I'm wondering if anyone has any insights into what might be causing this problem. Above is the BGP configuration on my routers for reference.

Thanks,

Sanju.

[Harold Ritter]

Hi @san ju. ,

Did you do a soft clear on the ISP session on R1 after changing the

route-map

?

clear bgp ipv4 unicast 175.32.118.12 soft out

Regards,

[san ju.]

Hi @Harold Ritter 

Yes, I have completed this task for all sessions by executing the following command,

clear ip bgp * soft out

Thanks,

Sanju 

[Harold Ritter · Accepted solution]

Hi @san ju. ,

And traffic is still coming via R1 after running soft reset?

If so, I would suggest you talk to your ISP (AS60849). They will be able to tell you why the traffic still goes through R1 even after prepending your ASN multiple times.

Regards,

[san ju.]

Hello @Harold Ritter,
Sure, I'll reach out to my ISP to verify the situation. Nonetheless, I want to express my sincere gratitude for your time and for providing me with the guidance on how to address this problem. I truly value your assistance.

Thanks,

Sanju.

[Harold Ritter]

You are very welcome @san ju. and thanks for the feedback