Cisco 6500 VSS Configuration Example

(Abhishek D) #41

Hi team

what is the dual-active detection concept ?
To achieve dual active detection - do we need to have separate link between both VSS chassis OR it is part of VSL ?


(Rene Molenaar) #42

Hi Abhishek,

If your VSL fails then the standby switch can’t tell if the active switch is still there or not. If the standby switch goes active while the active switch is still there, both will be active, forwarding packets and you’ll run into issues. This is called “dual active”.

Dual-active detection is configured outside of the VSL link. There’s enhanced PAgp, BFD and Dual-Active Fast Hello Packets to use. You can use one or all three at the same time.

Cisco has a pretty good document for this:


(Networklessons Admin) split this topic #43

19 posts were merged into an existing topic: Cisco 6500 VSS Configuration Example

(Helen N) #44

Is it necessary to use a port channel to configure vss?

I currently only have 2 sfps to connect two
4506-E switches

(Lazaros Agapides) #45

Hello Helen

The use of two or more links for the Virtual Switch Link (VSL) is only a recommendation by Cisco. It is not manditory. However, this is not recommended as VSS is designed to be a high availability system and by having only one link, this high availability is sacrificed. It should be implemented fully realising this. Ideally, you should purchase an additional module to implemente multiple links.

I hope this has been helpful!


(Jason F) #46

I’m sure I’m missing something here but if I were to use VSS on 2 layer 3 4500 chassis and wanted to connect a access switch to the VSS pair would I use a regular port channel to connect to the VSS pair from the access switch or is there an actual multi-chassis Ethernet port configuration I would need to configure between the access switch and the VSS pair? I’m just a bit confused as to what configuration I need to connect multiple access layer switches to the VSS pair. I’ve been trying to research it but am pretty confused about the topic as I’m not able to see a straight forward answer. Any clarification would be helpful.

(Lazaros Agapides) #47

Hello Jason

There is no special configuration that you need to apply to the access switch that connects via etherchannel to the VSS pair. From the point of view of the access switch, the etherchannel that is being configured would be exactly the same whether both (or all) links are connected to the same physical switch or if they are connected to both members of the VSS pair. The special configuration would be applied on the VSS pair side.

Take a look at the following Cisco documentation that describes such a configuration:

I hope this has been helpful!


(Inon L) #48

Hey, you mentioned that NSF and SSO don’t have to be configured but Cisco documentation says otherwise: “Configure SSO and NSF on each chassis”

Do I miss something here, or it’s something new that you aren’t familiar with?

(Lazaros Agapides) #49

Hello Inon

Yes, you are correct that according to Cisco documentation, both SSO and NSF are necessary in order for VSS to function. Rene doesn’t mention in the lesson that they don’t have to be configured, but mentions them as features and explains what they do. In any case, I will ask Rene to take a look and to make any clarifications necessary to the lesson to avoid confusion.

Thanks for bringing this up!