[c-nsp] OSPF fast convergence

Justin Shore justin at justinshore.com
Thu May 14 09:29:13 EDT 2009

Phil Mayers wrote:
> Justin Shore wrote:
>> Phil Mayers wrote:
>>> Common advice seems to be to make actual link-loss detection fast, in 
>>> preference to using BFD. That said, I know some people use BFD.
>>> Assuming you're using LAN cards, you may want to see if you can make 
>>> router links as routed rather than SVI interfaces. Though routed 
>>> interfaces are implemented internally as VLANs, presentations I saw 
>>> from Cisco claim that this:
>> I prefer to use BFD personally.  Link failure detection without BFD 
>> will be slow no matter what you do.  FRR doesn't gain you much if it 
>> takes you several seconds to realize that a link dropped.
> Seconds? Wow. I'm curious - under what circumstances are you seeing such 
> length link-loss detection times?

On our 7600s today.  We drop a link to one of them and the thing is 
oblivious to the drop for 2-3 seconds.  Dumber than a post...  L3 is 
waiting on L1 to wake up before it can start tearing down routing 
relationships and pulling routes.  I'm running SRB1 on my 7600s right 
now so that I can run BFD.  I'm trying to get my account team to carry 
my BFD on SVI request to the DE team for BFD or the product manager. 
Unfortunately I think I'm throwing pennies into a blackhole.


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