Recomendation for UDLD and Rapid STP - Best practice

[Kn1ghtR1d3rOfD00m]

Hello, 

Sorry I tried to find the best answer from the forum but did not find a best or solved one. 

Im trying to determine what would be the best practice or if it is recommended to use UDLD with Rapid STP? 

What I want to avoid is any kind of loop in the network due to the timers. so is it recommended to lower the Rapid STP times to avoid loop for the timers of the UDLD (45secs)?

is it recommended or is it feasible to use UDLD with RapidSTP? 

What times should I use with UDLD with Rapid STP?

is UDLD an old tecnology? 

What could be the final convergence time by using Rapid STP and UDLD?

Any feedback or help is really appreciated.

Thanks

[Reza Sharifi · Accepted solution]

Hi,

If you want to protect the network from STP failure than you may want to deploy loop guard instead of UDLD.

See below document:

http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10596-84.html#loop_guard_vs_uld

HTH

[Kn1ghtR1d3rOfD00m]

Thank you so much for the response. I'm checking the URL now and its got worth info. 

yes,  in fact, what we want is to enable UDLD with Rapid STP, but did not know if we have to modify the timers for the UDLD.

I was worried about the times for the UDLD working together with the RSTP.

Thanks

[Reza Sharifi]

Hi,

Just FYI, UDLD is usually deployed on fiber links, as you have 2 strands of fiber per connection and there is possibility of malfunctioning between transmit and revive strands.  Copper port usually don't have this type of issue.

HTH

[paul driver]

Hello

Loopguard and UDLD are similar but not the same.

My understanding is they both protect against loops caused by unidirectional links, but whereas with UDLD tests the physical bidirectional capabilities of the links , Loopguard does this by its receipt of BPDU's.

Thus UDLD can detect problems with physical links irrelevant of its receipt of any bpdu's.

So in summary I would utilise both features as UDLD will detect physical issues which loopguard will not and when used on an aggregated link will ONLY close down part of that aggregate.

Loopguard will detect missing bpdus when UDLD will not and when used on an aggregated link will close down ALL that aggregate link

res

Paul

[Kn1ghtR1d3rOfD00m]

Excellent, thank you., yes, in fact, I have seen our core devices with both. UDLD and loopguard, thank you for your clear explanation. I was worried about the UDLD times as some say that might cause loops if using UDLD and Rapid Spanning tree, but according to what you say, just by enabling UDLD and Rapid STP with its defaults, it should work like a champ I guess.