[c-nsp] OPSF / BFD timer advise [NC]

[david.ponsdesserre at sgcib.com]

James .

The number 4 means you are going to send 4 hello packets/seconds which is 
to my opinion really agressive . So depending on the load of your links 
you are going to end up with some neighbors down . 

Have a look here , it is pretty well explain . 
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120limit/120s/120s23/fasthelo.htm

I would suggest to mitigate this multiplier a little bit , don't forget to 
tune your SPF and LSA throttle . 
A good document to look at as well is this one: 
http://www.cisco.com/application/pdf/en/us/guest/netsol/ns432/c649/ccmigration_09186a0080811468.pdf

Hope this help 
Rgds
David 




james at tridentnet.net 
Sent by: cisco-nsp-bounces at puck.nether.net
12/07/07 15:04
Please respond to
james at tridentnet.net



To
philxor at gmail.com
cc
cisco-nsp at puck.nether.net
Subject
Re: [c-nsp] OPSF / BFD timer advise






Hi Phil

We have about 40 6509-sup720 running
's72033-advipservicesk9_wan-mz.122-18.SXF5' this particular site is
configured in a 4 core model.

I would agree with you that a 1sec OSPF dead timer is over kill,
especially as we have sub second timers on BFD. My only question now is
what people suggest we set the OSPF timers to?

As I understand BFD its able to detect link failure. The OSPF timer still
need to be quick enough to cause convergence should the problem not be
link failure or put another way as a back up to BFD.

We are not entirely sure what is causing the issue. The syslog only show
the OSPF neighbour as down. Strangely the outage can last a few minutes
before syslog reports the neighbour as back up and the M-VPNS are back up.


> What device and what IOS are you running this on?  Are the
> adjacencies are lost due to a BFD event or an OSPF dead timer
> expiration?  Using a 1 second dead timer and BFD-enabled OSPF is
> overkill imho, but you need to find out what is causing the failures.
>
> Phil
>
>
>
> On Jul 12, 2007, at 8:38 AM, James Worley wrote:
>
>>
>>
>> Ola Gents
>>
>> We are having a problem with OSPF neigbour relationships being
>> taken down
>> between core and distribution. This is causing our MPLS-VPNs to
>> fall over.
>>
>>  ip ospf dead-interval minimal hello-multiplier 4
>>
>>  bfd interval 250 min_rx 250 multiplier 4
>>
>> looking at the config above it looks like my company is running sub
>> second
>> timers on both BFD and OSPF and a possible reason for an overly
>> sensitive
>> network.
>>
>> My feeling is we need to let off on the OSPF timers and allow BFD
>> to do
>> its job. Possible configure a 1sec hello and 3 dead timer for OSPF?
>>
>> Anyone fancy commenting?
>>
>>
>> Kindest Regards
>> James
>>
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>
>
>
>


Kindest Regards
James

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