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SPF Timer

I want using a BFD with OSPF . but, fault tollerence time is BFD hold time + SPF recalculation interval.

so that, I want to change SPF timer.

I read it this document.

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1838/products_feature_guide09186a0080134ad8.html

but, I don't understand command option spf-hold and spf-max-wait.

timers throttle spf spf-start spf-hold spf-max-wait

In the OSPF router. to occur route change then, after spf-start interval excute SPF calculation.

but, SPF calculation is occured just one time. I don't understand what is spf-hold and spf-max-wait.

Any one help me?

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: SPF Timer

Hi,

There are 3 parameters of interest:

spf-start:

this is the time between the first topology change event and the calculation of the SPF. This timer kicks in if there has not been a topology change for a little while. This is typically a very small value.

spf-hold:

this is the minimum time between the first SPF calc after an idle period and the next SPF as a result of a topology change. This is typically a larger value than the spf-start time. If topology change events continue to occur, the wait interval between SPF runs will continue to double at (starting at double the spf-hold) until they reach a value of spf-max-wait

spf-max-wait:

this is the maximum time interval between successive SPF runs.

So what does all that mean ? It simply means that these parameters offer you fine-grained control over how frequently the SPF is scheduled. If you have a quiet network, a low spf-start will mean that the SPF will be calculated as soon as a topology change occurs. However, if a lot of these events are occurring, you could kill the router just from the SPF calcs. Therefore, the spf-hold and spf-max-wait timers ensure that in the face of continual change, SPF is not run too frequently. This is just a safety net to give you quick response when needed but to slow down if required.

Hope that helps - pls rate the post if it does.

Paresh

1 REPLY
Purple

Re: SPF Timer

Hi,

There are 3 parameters of interest:

spf-start:

this is the time between the first topology change event and the calculation of the SPF. This timer kicks in if there has not been a topology change for a little while. This is typically a very small value.

spf-hold:

this is the minimum time between the first SPF calc after an idle period and the next SPF as a result of a topology change. This is typically a larger value than the spf-start time. If topology change events continue to occur, the wait interval between SPF runs will continue to double at (starting at double the spf-hold) until they reach a value of spf-max-wait

spf-max-wait:

this is the maximum time interval between successive SPF runs.

So what does all that mean ? It simply means that these parameters offer you fine-grained control over how frequently the SPF is scheduled. If you have a quiet network, a low spf-start will mean that the SPF will be calculated as soon as a topology change occurs. However, if a lot of these events are occurring, you could kill the router just from the SPF calcs. Therefore, the spf-hold and spf-max-wait timers ensure that in the face of continual change, SPF is not run too frequently. This is just a safety net to give you quick response when needed but to slow down if required.

Hope that helps - pls rate the post if it does.

Paresh

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