VSS-Dual Active Scenario

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Mar 30th, 2010
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I have configured VSS with cat 6509 switches and is working fine.The VSL link is configured with 10G ports on Sup 720-10g card (5/4 & 5/5).when i was doing the testing for the dual active detection by removing both vsl links,the current active switch was becoming inactive with all interafces shutdown and old standby switch was becoming active and carrying the traffic without any drop.when i was reconnecting teh VSL link, ideally the old active switch should aitomatically reboot and join the clutser as standby but same was not happening.the message i was getting was dirty configuration exists to manually save the configuration and reload the switch.Actulally no configuration wa schanged during dual active condition.Same was checked with how switch virtual redundancy config-mismatch and the output was no config mismacth.Same thing we tried multiple time but same was the result.

finally we shifted the one of the vsl link port from Sup720 to line card in the chassis with 10G port so now the vsl link was comparised of 1 port from sup720-10G and another port from 10G port from line card.post this configuration teh VSS cluster came up and when we tested the dual active scenario again it was working fine.when we reconnected the both the VSL links,old active switch whose intefaces were shutdown due to dual active condition,rebotted and came up in vss cluster as standby.

can anyone please confirm what was the exact problem here.

s72033-advipservicesk9_wan-vz.122-33.SXH5.bin is the software.
VS-S720-10G is the Sup engine
WS-X6708-10GE is teh line card.

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Giuseppe Larosa Tue, 03/30/2010 - 05:22
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Hello Sameer,

you should add at least what dual detection method is used on this VSS in order to start a discussion.

Posting a filtered version of VSS config would be of help too.

without this key information it is difficult to say something meaningful.

Hope to help


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sameermunj Tue, 03/30/2010 - 22:45
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Thanks for the reply..

Just to update you on the same,PAGp is used for the MEC between 4500 and VSS and IP BFD is configured for connectivity between Nexus and vss as nexus doesnt support pagp.Dual active detection methods workings fine and thats not the issue.

As mentioned in my previous post,now the vsl link configured using 1 port from sup 720-10G and 1 port from line card.Now when i remove both the vsl link ports dual active detection happening and when i restore the VSL connectivity,the old active switch reboots itself and join the vss cluster again as standby which is absolutely ok as per vss design.

only concern is when both VSL links ports were on Sup-720, it was not working and required to do manual reboot for the old active switch to join back the cluster as standby post VSL restore actvivity.without any other change in configuration same is working when we shift one of teh vsl link to line card.

i need to find the reason for the same.the message i was getting is dirty configurtion (onfig change during dual active condition) which was actually not the case.


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