VSS basic questions

[gautamzone]

Dear Friends,

Just a few basic questions on dual-active setup in VSS:

We have a scenario on 2 VSS chassis each of them having 1 6708 and 1 VS-720 supervisor. There are no 1G ports except the one on the supervisor.

We are using 2 VSL links - one on 6708 and other on Sup. We are using the dual-active link on the Supervisor for dual-active detection recovery.

Edge switches are 3750-X running LACP.

Please correct my understanding on the below:

a.If 6708 fails, then one VSL link will fail. However, the other VSL link will be operational and the dual-active link will also be operational.

b. If VSL link on supervisor fails, then the VSL is still operational over 6708 card and dual active link will also be operational.

c. If supervisor fails, then both VSL links will fail, dual-active link will fail, the VSS standby will take over as active.

If supervisor fails on a VSS switch, then all line cards on that switch too fail. Right?

Is there a scenario where both VSL links will fail without Sup or switch failure? 

If the Sup or switch fail, we have VSS standby taking over as active. Right?

In such a case, where does a solution like Dual active really help??

If we need to use dual active, can we use 10G link too on either of these line cards?

Please clarify.

Thanks a lot

Gautam

[Rahul Kachalia]

Hello Gautam,

   Following is the response to your queries:

a.If 6708 fails, then one VSL link will fail. However, the other VSL  link will be operational and the dual-active link will also be  operational.

rahul>Correct.

b. If VSL link on supervisor fails, then the VSL is  still operational over 6708 card and dual active link will also be  operational.

rahul>Correct.

c. If supervisor fails, then both VSL links will fail, dual-active link will fail, the VSS standby will take over as active.

rahul>Correct.

If supervisor fails on a VSS switch, then all line cards on that switch too fail. Right?

rahul>Correct

Is there a scenario where both VSL links will fail without Sup or switch failure?

rahul>Yes, these could be driven based on fiber-cuts or high error rate on VSL intf caused by bad connectors/cables. In both cases, VSL protocol communication between both virtual-switch nodes will fail to communicate and may trigger dual-active condition  in the network. Detection & recovery process will be done on mechanic you implemented, i.e. fast-hello or PAgP+

If the Sup or switch fail, we have VSS standby taking over as active. Right?

rahul>Yes, current VSS HOT_STANDBY chassis will transition in ACTIVE role when it detects loss of communication with current ACTIVE switch that could be caused due to chassis, supervisor or all VSL link fault condition.

In such a case, where does a solution like Dual active really help??

rahul>As I described earlier, dual-active is the condition where supervisor module on each virtual-switch is in operational state however loss all VSL links, in this condition both switches cannot synchronize and maintain system virtualization.

If we need to use dual active, can we use 10G link too on either of these line cards?

rahul>Yes, fast-hello is media-independent. Note, unlike VSL the fast-hello links cannot be in your data transit path hence using on-board supervisor 1G port is more cost-effective solution. However if you have Quad-sup network design in that case you may to use one of module link to enable fast-hello. See following design guide for more details about Quad-sup:

http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/Borderless_Campus_Network_1.0/Borderless_Campus_1.0_Design_Guide.html

thanks,

rahul.