udld agressive mode on vpc peer-links?

[sandevsingh]

Hi, is it a good practice to enable udld agressive mode on the vpc peer links? Are there any caveats to it?            

[Reza Sharifi · Accepted solution]

Yes, it is actually recommended by Cisco.

from the config guide:

We recommend that you configure Unidirectional Link Detection (UDLD) on both sides of the vPC peer link

Here is the link:

http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/interfaces/configuration/guide/if_vPC.html

HTH

[sandevsingh]

Thanks Reza, should I also configure "errdisable recovery cause udld" along with it? I believe this will automatically recover a port in err-disable caused by udld, BUT isn`t it always better to have them stay in err-disabled condition in order to avoid any STP loops? And then you manually intervene and troubleshoot rather than auto-recovery?

[Reza Sharifi]

Hi,

Yes, the "errdisable recovery cause udld" will start a timer and once the timers expires, it will enable it.  I agree with you, if you want the link to go to errdisable, then you want to recover it manually and find out what cause it, if not with recovery you may never know what happened.

That is just my opinion

HTH

Reza

[Bibhas Mattoo]

I know that it's too late on this post; however, it's not actually recommended to have UDLD aggressive mode configured on VPC Peer-link and/or VPC links.

Aggressive mode timers are too sensitive for control-plane traffic and we have seen alot of issues because of it configured on the VPC links. On ports where LACP is already configured, there's no need of UDLD at all. On the other links where LACP isn't configured, UDLD normal mode at most should be used.

Same has been mentioned in the link shared earlier by Reza:
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/interfaces/configuration/guide/if_cli/if_vPC.html

While you configure Unidirectional Link Detection (UDLD), note the following recommendations:

• If LACP is used as port-channel aggregation protocol, UDLD is not required in a vPC domain.
• If LACP is not used as the port-channel aggregation protocol (static port-channel), use UDLD in normal mode on vPC member ports.
• If STP is used without Bridge Assurance and if LACP is not used, use UDLD in normal mode on vPC orphan ports.

Regards,

Bibhas