Shulou(Shulou.com)06/01 Report--

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In the production environment, we often separate one of the Nexus switches from the vPC domain, such as upgrades or disaster recovery drills. But one of the details is the state of the Sticky Master that few people notice, so this can lead to network outages.

In the vPC environment, two vPC will conduct role election, through the priority configuration, assuming that the N7K-1 is primary,N7K-2 and secondary.

Step one

When we separate N7K-2 from the vPC environment, we disconnect the peer-link, keepalive and all uplink and downlink interfaces of N7K-2.

At this time, the two devices are in a dual active state, and N7K-1 is primary,N7K-2 and secondary,operational primary.

Of course, because N7K-2 is not connected to the network, the network does not have any impact.

Step two

When we complete the operation on N7K-2, connect the N7K-2 back to the network. At this time, we will generally see that N7K-1 has become the vPC interface of primary,operational secondary and all suspend.

Doubt

Why does N7K-1 become primary,operation secondary when two devices are connected when primary,N7K-2 is clearly secondary,operational primary?

Sticky Master

This is because in vPC, there is a parameter called Sticky Master. When a Secondary becomes operational primary, it sets its own Sticky Master to True.

Because N7K-1 has always been Primary,Sticky Master, it has always been FALSE,N7K-2. Because role has been switched from Secondary to Secondary, operational primary,Sticky Master has been set to TRUE.

In this case, once the two devices re-establish the vPC relationship, the device with Sticky Master set to True will remain Role, and the device with Sticky Master set to False will choose another available role, that is, primary,operation secondary.

Therefore, N7K-1 will converge, suspend all vPC interfaces, re-check the interface status, and restore the interface. At this time, if the vPC interface on the N7K-2 is not up, it will lead to network outage.

Equipment access check

This situation can be avoided. The Sticky Master check is performed before the new device joins the VPC domain. Using the show system internal vpcm info global | I Sticky command, you can see the following two situations:

Case 1: NX-OS# show system internal vpcm info global | i StickySticky Master: TRUE

You can't access the network at this time, otherwise it will preempt the Role of the current Primary.

Case 2 NX-OS# show system internal vpcm info global | i StickySticky Master: FALSE

At this time, you can access the network and automatically become a Secondary.

How to reset Sticky

Once you check that Sticky Master is TRUE before joining the network, you need to reset the status to FALSE.

There are two ways to reset:

1. Reconfigure the priority, even if the priority is the same.

Vpc domain 110 priority 32768

two。 If the configuration priority cannot be reset, the only thing to do is to restart the device.

Reference:

[1] http://www.cisco.com/c/en/us/support/docs/interfaces-modules/nexus-7000-series-supervisor-1-module/119033-technote-nexus-00.html?dtid=osscdc000283

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