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BGP weird behavior

krishnadig
Level 1
Level 1

Hi Friends,

I am facing a weird issue with BGP routing in Nexus 3k (NX OS 6). 

Router A (AS 6500) and B (AS 6600) are eBGP peers. 

Router A:

int Eth1/1.100 (no vrf) IP 1.1.1.1 & peer 2.2.2.2

int Eth1/1.200 (vrf test) IP 10.10.10.10 & peer 20.20.20.20

Router A BGP config:

router bgp 64100
  log-neighbor-changes
  address-family ipv4 unicast
  neighbor 2.2.2.2 remote-as 6600
    local-as 65500 no-prepend replace-as
    timers 1 3
    address-family ipv4 unicast
    soft-reconfiguration inbound always
vrf test
    address-family ipv4 unicast
neighbor 20.20.20.20 remote-as 6600
      local-as 65500 no-prepend replace-as
       address-family ipv4 unicast
       soft-reconfiguration inbound always

 

There are 2 instances of BGP running on Router A with same local & remote AS; one in global routing table and other in VRF test. The BGP adjacency comes up fine between the peers one at a time; however I have noticed that only 1 BGP session remains in "established" state at a given point of time - either the one in global routing table or the one in VRF Test. And the other one goes to Idle / Active state. If I clear BGP session for the idle/active one, it comes up and the other one goes down.

 

Is this normal? Or is there flaw in the design? How do I overcome this scenario?

6 Replies 6

Hello.

From the configuration I don't see: ebgp-multihop and update-source - this could be a reason!?

Hi, thanks for responding. I dont think so; however as I mentioned, one works at a time. So if it would have been an issue of reachablity, it would have never come up.

thx

Hi,

I had raised a Cisco TAC and understood there is a bug in Nexus for the OS used on my device. BTW, its nothing to do with BGP.

https://tools.cisco.com/bugsearch/bug/CSCuw02851

 

Hello.

could you please share your service request (SR/ticket) number?

Hi, here it is 636628533

The issue is with ACL applied to one sub-interface impacts the other sub interface (with same physical interface). So I prepared just 1 ACL, with the intersting traffic for both sub-interfaces, and applied it to both. Its working now.

I will have to manage it with this workaround until Dec 2015 end, until the OS with bug fix is released.

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