Help in understanding VSS

[JohnTylerPearce]

I understand that VSS works with Cisco Catalyst 6500 Series Switches. I know that the VSL or Virtual Switch Link between the

two switches allow for the switches to communicate control plane and data. From what I have read, you can have a maximum

of 8 10 gig links in the VSL.

So lets say we have two Cisco Catalyst 6500 Series Switches, with 20 access switches. We setup the two 6500 series switches

to run VSS. Now, that we have VSS, the two switches are basically one logical switch, with one as active and one as standby.

So on our 20 access switches, we have one connection to one of the 6500 switches. If it's one logical switch, than each access

switch doesn't have redundant links so there would be no loop to occur.

Now, lets say I'm wanting to run MEC on all my access switches. I would assume I could configure 2 ports on each access switch,

each one going to a member in the VSS, which would also be loop-free as well, except for we have redundant paths to the 6500

than just one in my first example.

So how much do I have right and how much do I have wrong?

[Mohamed Sobair · Accepted solution]

Hi John,

The Proper design approach is to have each of the Access Switches dual linked to both chasis, this will provide you with redundancy incase of a VSL link failure or incase of a single hardware chasis failure.

You can benefit of having the VSS chasis aggrgate all Access Switches dual links by having Eitherchannel Configuration which allows you to benefit of higher uplink throughput.

This Scenario is absolutely loop-free, and incase of a VSL link failure, the default behaviour of the Switches is to revert back to Stand alone Setup.

Regards,

Mohamed

[JohnTylerPearce]

So, if let's say the VSL link fails, it will revert back to Stand Alone setup, but will it then run regular STP? Since,

VSS is not operation then?

[Mohamed Sobair]

Surely it will run regular STP and you will still be having both links from the Access Switch in STP forwarding state.

Regards,

Mohamed

[JohnTylerPearce]

That would make sense since one of the connections would have to the root port and the other would be designated

toward the other Stand-Alone 6504?

[Kishore Chennupati]

Hi John,

Thats right. STP will do its stuff and decide which port will be RP and FWD etc. Just the normal STP stuff.

Essentially VSS is to tap onto more Banndwidth with the Data center virtualisation and incrementing bandwidth requirements. Whilst implementing VSS you are sort of disabling STP between the Access and Dist switch with port channel capability so you double bandwidth and no loops.  Having said the above it doesnt mean that STP is completely disabled. NO. Its just sort of bypassed with VSS. As mohammad said when the VSL goes down then its back to the normal operation of STP

This is similar to vPC in Nexus land.

HTH

Kishore

[JohnTylerPearce]

Thanks for your help guys.