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krishnadig
Beginner

CIsco VSS recovery mode

Hello Friends,

Cisco VSS is configured on a pair of 6500 with single SUP VS-S720-10G on each of them. Its configured for dual active detection (fast hello).

Query is -

When the standby chassis goes down - either due to SUP failure or power failure or VSL link fail

How does VSS decide, if the active chassis has to be in "recovery mode" or remain active.

I tested removal of VSL links - active chassis moved to "recovery mode" & in next test checked shutting down standby chassis - active chassis was in same state.

How does it determine peer failure and which mode it has to transition to?

1 ACCEPTED SOLUTION

Accepted Solutions
Rolf Fischer
Engager

Hello,

- either due to SUP failure or power failure or VSL link fail

we need to distinguish between a VSL fail and a failure of one of the chassis.

When the VSL fails, the dual-active detection mechanism still communicates between the two Sups and is therefore able to detect the dual-active condition and then put the former active Sup in recovery mode in order to prevent anything worse.

When, however, one of the chassis fails, the dual-active detection communication will also fail and in such a case there is no reason for a transition into recovery mode for the remaining chassis. Btw: When you remove the fast-hello link in a stable VSS (or a ePAgP channel goes down),  you only loose a dual-active detection mechnism - it will not affect the VSS roles. That's why it is recommended to use more than one dual-active detection mechanism (if possible).

Hope this makes sense.

Regards,
Rolf

View solution in original post

4 REPLIES 4
Rolf Fischer
Engager

Hello,

- either due to SUP failure or power failure or VSL link fail

we need to distinguish between a VSL fail and a failure of one of the chassis.

When the VSL fails, the dual-active detection mechanism still communicates between the two Sups and is therefore able to detect the dual-active condition and then put the former active Sup in recovery mode in order to prevent anything worse.

When, however, one of the chassis fails, the dual-active detection communication will also fail and in such a case there is no reason for a transition into recovery mode for the remaining chassis. Btw: When you remove the fast-hello link in a stable VSS (or a ePAgP channel goes down),  you only loose a dual-active detection mechnism - it will not affect the VSS roles. That's why it is recommended to use more than one dual-active detection mechanism (if possible).

Hope this makes sense.

Regards,
Rolf

Hi Rolph

Does that mean in case if all the VSL link fails between two switches, then we need to reload manually to recover the switch from recovery mode ?

Is there any other way to come out of recovery mode automatically in such a scenario ?

Br//

Rohit Gupta

The switch recovers automatically as soon as the VSL is operational again, so the only manual action should be to re-establish the VSL again.

VSS Dual Active Recovery Actions:

"An active chassis that detects a dual-active condition shuts down all of its non-VSL interfaces (except interfaces configured to be excluded from shutdown) to remove itself from the network, and waits in recovery mode until the VSL links have recovered. You might need to physically repair the VSL failure. When the shut down chassis detects that VSL is operational again, the chassis reloads and returns to service as the standby chassis.

Note: If the running configuration of the chassis in recovery mode has been changed without saving, the chassis will not automatically reload. In this situation, you must save the running configuration and then reload manually."

HTH
Rolf

krishnadig
Beginner

Thanks Rolf. clear now!!