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BGP Flapping Issue due to over utilization of link

Can we find a way to enhance BGP stability when we are running on reduced IMA bandwidth.

Our router has 3xT1 IMA, when all 3 T1s are running properly, we have no problems. When a Layer 1 issue occurs on one of the T1s (reduced bandwidth) then the router becomes highly unstable (BGP timeouts/flapping). BGP flaps continuously when we lose a T1, and then the service is unavailable.

Is there a way to create a policy map that will give BGP priority, so we will not experience an "outage" during a layer 1 issue? In other words, BGP will get a level of priority to insure it does not FLAP continuously.


Re: BGP Flapping Issue due to over utilization of link

I also thought policy-map could be of help here. But one thing to note, best practice is to create a bgp neighbor with loopback address & not physical interface address. If your neighbor is configured on physical interface address & that interface goes down, then you'll loose connection. But if you are already using loopback for neighborship, the here is the policy-map:

BGP runs by establising tcp connection with neighbor over port 179. So you may cretae a policy map & reserve BW for connections with tcp port 179.

access-list 101 permit tcp any any eq 179

clas-map neighbors

match access-list 101

policy-map bgp

class neighbors

bandwidth 100

apply this policy-map to either the physical links or multilink connecting to the neighbor devices.

hope that clarifies.

pls rate all helpful posts.

Re: BGP Flapping Issue due to over utilization of link

As BVS said, it is always advisable to use the loopback interfaces with BGP

So in case you use loopbacks just prioritise all the traffic between the 2 loopbacks using an access-list which will prioritise all the BGP traffic

access-list BGP permit ip host Loop1 hostloop2

access-list BGP permit ip host Loop2 host loop1

clas-map match-all BGP

match access-list name BGP

policy-map bgp

class BGP

bandwidth 100

Apply this policy on the interface on both ends of the routers



Re: BGP Flapping Issue due to over utilization of link


In addition to BVS and Narayan:

Loopback IP Address can be used in BGP for Tunnel Source and Destination. That should be highly enough.

>>If you have enough Bandwidth there is no need for reserving BW to Port 179 - the BGP TCP connection port.

Since you have overloaded Link pls go-ahead with their advices.


Best Regards,

Guru Prasad R