vss and nexus

[sai shiva prasad]

Hello all,

I wanted to migrate from cisco catalyst 6506 to cisco 4510 r+e and bring v.s.s up in a campus. so I have few questions regarding port channel config.

we have nexus 5k as downstream devices and is it good way to have all the downlinks to nexus from vss in a single port channel. since it is a v.s.s.

I am asking this because in another campus we have downlinks to nexus from vss by different port channels.

[nazimkha]

If you have a single port-channel on the Catalyst VSS side than you need to configure vPC on the nexus side. So it would be a single port-channel.

If you have only VSS on the catalyst, then you still need to have different port-channel i.e one port-channel for each nexus switch.

I hope it answers your query. Although, I would have loved to explain it with some topology.

[balaji.bandi]

nexus 5K are in vPC or standalone devices ?

[sai shiva prasad]

Hello all,

nexus devices are in vpc mode. But the thing is for one of our campus we have different port channels from v.s.s to nexus 5k. I want to know which is the best practice and why ?? below is the second diagram of vss nexus (vpc) port channel configuration. which is the best way ?? both are new campuses and we didn't have any outages till now.....but for new campus I just want to know which is the best practice from the two diagrams

[balaji.bandi]

Mesh network always best for the fully redundant, you can also do vPC with downstream, so you can minimise spanning tree.

[sai shiva prasad]

port channels from nexus (each device) to the vss are already in vpc.

[nazimkha]

Should be as per attached topology i.e a single port-channel from VSS as well as the vPC side

[sai shiva prasad]

Thank you nazimkha

so you agree that the port channel config on first picture is the right way... but I need to understand why it is right way and why not the second picture 

[nazimkha]

One port-channel will give total aggregate bandwidth of 4 links i.e if you have 10G ports you will get 40G port-channel whereas if you do 2 port-channel STP will block one of them and the effective aggregate would be only 20G

[sai shiva prasad]

when we have single port channels from vss to two nexus devices and also from each nexus switch to avoid stp blocking the ports. 

as per your suggestion if i go with this, then we might have more bandwidth between nexus and vss since none of the ports will  be in blocked state either on nexus or on vss....since vss is considered as a single channel.

Thank you for your reply nazimkha......thanks a lot

[sai shiva prasad]

since vss is considered as a single CHASIS*

[balaji.bandi]

Yes correct. you have more advantage when you go with vPC.

[nazimkha · Accepted solution]

Yes with vPC and VSS we present the two switches as single switch.

If you think your query is answered ,please mark the post resolved.