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ISIS + BoB/BLB + Flapping

FrankHu114051
Level 1
Level 1

We have 2 ASR9K connect by BE interface and we run ISIS between them. I have 2 questions, (1) How ISIS works with BLB in this case, what are the commands to check if ISIS+BFD is working properly ?(2) If the BE interface is flapping somehow and I don't want ISIS flaps (in another word to stop running ISIS over this BE during the flapping) how do I configure it and how we can test in the lab to check our configuration is working properly? Thanks! Frank

4 Replies 4

Hello,

 

the command:

 

show bfd session

 

can be used to verify the status of the session...

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello @FrankHu114051 ,

one of the most interesting features of IOS XR is the per member link BFD on BE bundle

see

https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r7-1/routing/configuration/guide/b-routing-cg-asr9000-71x/b-routing-cg-asr9000-71x_chapter_0100.html#ID670

 

This is the recommended way to configure BFD on a BE bundle, because actually there is a BFD session over each member link allowing for faster detection of a member link failure of the bundle-ethernet.

 

" The BFD agent on each bundle member link monitors state changes on the link. BFD agents for sessions running on bundle member links communicate with a bundle manager. The bundle manager determines the state of member links and the overall availability of the bundle. The state of the member links contributes to the overall state of the bundle based on the threshold of minimum active links or minimum active bandwidth that is configured for that bundle. "

 

>> If the BE interface is flapping somehow and I don't want ISIS flaps

if the whole BE interface is flapping this means that the bundle is not stable

 

A possible can be the support of dampening over the BFD session

 

>> The dampening command was added to minimize BFD session flapping and delay session startup. 

 

However, when using BFD the basic idea is to make the routing protocols IS-IS or also others as much as reactive as possible without increasing the use of main CPU on the route processor.

So this second request is in some way the opposite.

 

note: with per member link BFD you will get a BFD session over each member link but IS-IS hellos are sent only 1 per direction and over an active link using non IP load balancing scheme.

 

Hope to help

Giuseppe

 

 

Just out of curiosity (and since I could not find any information related to ISIS in this regard):

 

What is BoB/BLB ?

Hello Georg,

I'm not sure but I suppose that BoB may be BFD over Bundle Ethernet that is the feature I have mentioned in my previous post.

BLB might be load balancing over Bundle-Ethernet

 

Let's wait for the OP to tell what he means with these

 

Hope to help

Giuseppe