Nexus7700, vPC role preemption problem

[ngtransge]

Hello,

I have very strange behavior on vPC. Hardware is Nexus 7700 F3 and NX-OS 6.2(12). Two switches are placed in vPC domain. The vPC peer link is organized by two 10Gb links. Keep alive link is configured on sup interfaces, over different management network. Auto-recovery feature in enabled by default.

The problem is that when I reload N7K-1 vPC primary device, secondary N7K-2 becomes primary. But when N7K-1 boot, it takes over its vPC primary role, this forces N7K-2 to bounce its vPC ports, so all its ports goes in shutdown and then enabled.

Do you have any idea why this may be happening?

This behavior of bouncing ports on N7K-2 negatively affect network operations, and increases convergence.

According to documentation this is not normal behavior.

Thanks in advance,

San

[Rajeshkumar Gatti]

Hi San,

I think I answered your post on a OTV convergence issue. Seems liek you are having some interesting problems with F3/6.2.12. I have done some test with this hardware and code and have never run into this issue hence I feel this is not an expected behavior especially when you are reloading the switch.

The only time you can see this is during the following sequence - Shutdown peer link and peer keep alive and then reload. This will cause the switch to come up as a primary causing dual active scenario with the existing 7k already up and running. When the peer keep alive and peer link is brought back up then VPC role negotiation could cause the VPC links to flap causing a down time.

This is not your scenario so I would open a TAC case if you can reproduce it.

-Raj

[ngtransge]

Hello Rajeshkumar,

Thank you for answer.

I have determined why this behavior was happening. The problem was that STP Pseudo root priority  for some non vPC vlans was higher than normal STP priority.  After I make STP pseudo root priority less that normal STP priority. The abowe described behavior was not observed.

[Rajeshkumar Gatti]

Hi San,

Thank you for sharing the resolution. Theoretically I cannot relate the STP pseudo configs with the vpc role preemption. Probably there is more to it then just a simple VPC setup which I could be missing. In future if I do run into something similar this resolution step would be something I will keep as a possible option.

Thanks,

Raj