VSL redundancy in a VSS

Unanswered Question
May 28th, 2009

I have been reading up on best practices for VSS and I keep coming up on the recommendation to not use only the Supervisor ports for the VSL. I'm trying to figure out why this is.

It's my understanding that it the Sup fails, the chassis will go down.

Anbody have any insight into this?

I have this problem too.
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lamav Thu, 05/28/2009 - 17:30


I havent read the document youre talking about, but as a rul of thumb, you should always use module diversity when creating port channels. This is just a best practice. So, if I have 4 gig links between 2 switches in a port channel, I am not going to use ports 4/1 through 4/4 because if that module goes down, im screwed.

Maybe that is what they are talking about.


Leo Laohoo Thu, 05/28/2009 - 17:47

I would be reluctant to use the Sup's ports (fibre or copper) to pass traffic in case my Super card fails.

I agree with Victor by spreading your uplinks into two cards/blades.

The only time I will use these ports is when it's only in a temporary basis, such as waiting for a new card to arrive but never long term.

francisco_1 Fri, 05/29/2009 - 06:33

The VSL EtherChannel supports only 10-Gigabit Ethernet ports. The 10-Gigabit Ethernet port can be located on the supervisor engine module or on one of the following switching modules:

•WS-X6708-10GE-3C or WS-X6708-10GE-3CXL

•WS-X6716-10GE-3C or WS-X6716-10GE-3CXL

cisco recommend that both of the 10-Gigabit Ethernet ports on the supervisor engines is used to create the VSL between two chassis.

Also the option to add additional physical links to the VSL EtherChannel by using the 10-Gigabit Ethernet ports on WS-X6708-10GE or WS-X6716-10GE switching modules.

Pls rate..


Giuseppe Larosa Fri, 05/29/2009 - 08:46

Hello Matthew,

VSS provides the capability for the surviving SUP to control both chassis.

For this reason it is recommended to provide interconnection also with 10 GE link(s) on separate linecards.



And it is for this reason that only one supervisor per chassis is supported with VSS.

see the VSL as a way to export the backplane and the control channels for this reason you need the new supervisors that are designed for this

if I take a sup720 3BXL I can use a 10GE linecard to build a link but the capability to export backplane/control plane is not present.

Hope to help


jpoplawski Fri, 05/29/2009 - 13:40

You are correct, if the SUP fails you will lose the chassis. However if you drop a GBIC, cut the fiber or accidently shut both TenGig ports, you'd be covered. It's alot harder to do

interface range ten 1/5/4 , ten 1/1/48


then it is

int range ten 1/5/4 -5


Physically diversifying the Port channel is the main idea, granted you have the extra tenGig ports to spare. It'll will work either way, granted you have spare tenGig slots.

Hope this helps, rate if it does!



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