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VSS - what happens when a supervisor fails?


We've been mocking up a test lab to test VSS on two 6500's.  Each 6500 has one sup720 and a 6708-10ge blade and we've established the two 10ge links between the two chassis; the first from the each chassis' sup and the second from each 6708.

My question is, what happens when the supervisor fails on one of the chassis?

I was under the impression that NSF and SSO would kick in and the entire VSS would be managed by a single sup.  If the active sup fails, the stby becomes the active and vice versa.  However, when we pulled out the active sup720 linecard (chassis1), the stby sup720 (chassis2) failed over as planned, but access to all of the linecards in chassis 1 were lost.

Is this how it's supposed to react?

11 Replies 11

Jerry Ye
Cisco Employee
Cisco Employee

Yes. When the SUP failed/removed, the fabric/bus on that chassis is down also.



That's odd.  I thought the whole point of VSS was to be able to manage two chassis via a single sup if necessary.  Otherwise, what's the real benefit?

quoting from the doc found here:

What is a VSS1440?

A. VSS1440 refers to the VSS formed by two Cisco Catalyst 6500 Series Switches with the Virtual Switching Supervisor 720-10GE. In a VSS, the data plane and switch fabric with capacity of 720 Gbps of supervisor engine in each chassis are active at the same time on both chassis, combining for an active 1400-Gbps switching capacity per VSS. Only one of the virtual switch members has the active control plane. Both chassis are kept in sync with the interchassis Stateful Switchover (SSO) mechanism along with Nonstop Forwarding (NSF) to provide nonstop communication even in the event of failure of one of the member supervisor engines or chassis.