dual active VSS chassis: what happens during recovery of VSL ?

gnijs · ‎04-05-2012

Hello all,

I have a strange question: suppose you have a VSS setup which has lost its VSL link (and you don't have any dual active detection, you lost that also).

Then both chassis will become active.

My question is: if a single VSL link now returns to up, which of the two chassis will reboot ? Is this always the same chassis ? for example

the chassis with the lowest priority ? (for example, suppose the VSL link is flapping)

GN

Reza Sharifi · ‎04-05-2012

Hi GN,

As soon as you connect the VSL link to both switches again, the primary switch will reboot and the stand-by will take over.

BTW, this is not a strange question at all. It is actualy a good question and requires some testing which I have done in the past.

HTH

gnijs · ‎04-05-2012

Reza, my question is when both switches are active (NOTE: NO dual active detection is enabled), which one is the primary and which one is the standby (?? i think there is no standby..)

If i read this document

http://www.cisco.com/en/US/products/ps9336/products_tech_note09186a0080a7c837.shtml#vsl_llr

when a vsl link comes up, then there will be the role-resolution-protocol. If this protocol sees both active, i hope it will look at the switch priority and reboot (?) or join the switch with the lowest prio in standby mode (without reboot ?). I don't know...

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You might ask: why would you not implement dual-active detection ? i am in a very specific and strange topological setup. The fail scenario i am investigating will lead to complete loss of VSL, complete loss of all fast-hello and dual active detecting links, AND one VSS chassis will also completely loose its uplinks to the rest of the network. In this case, actually, i don't care if it becomes "active" , it is completely isolated from the rest of the network. However, when the VSL recovers, i want to make sure that -the other- chassis (that has also become active but still has uplinks) MUST continue to run. If any chassis needs to be rebooted to join the vss as standby, it must be the one that was previously isolated.....