Can We configure VSS on Cisco Nexus Switch

[MOHAMMAD RAZA]

Hi,

Can we configure VSS on cisco Nexus switch, if don't then what is the alternet solution for redundancy on this switch.

[Steve Fuller]

Hi,

The Cisco Nexus products don't support VSS, but are able to provide similar capability i.e., Multi Chassis Link Aggregation, using the Cisco virtual Port Channel (vPC) feature.

You can find an overview of the feature and how to configure it on the Nexus 5000 series switch in the Virtual PortChannel Quick Configuration Guide.

Regards

[Kevin Dorrell]

Nexus switches do not support VSS, but they do (mostly) support an alternative call vPC (virtual port channel).  Just as VS is compatible with conventional EtherChannel, so is vPC.

The main difference is that with VSS, you have a single control plane that controls both switches.  One switch has the active control plane, and the other is in standby.

With vPC, both control planes are active at the same time, and they synchronise along the vpc peer-link. It is therefore vitally important that the two control planes are configured independently but identically.  There is a complex set of rules that determine what happens if the two boxes do not agree, for example about which VLANs are allowed on a particular trunk.

Hope this helps.

Kevin Dorrell

Luxembourg

[Jon Marshall]

Just to add to the others.

vPC is a redundancy feature for connecting to other devices. VSS is far more than that. It is a fully redundant setup because, as Kevin says, there is only one control plane for both switches.

So with VSS you only configure the active switch and the configuration is applied to both switches. Both switches are capable for forwarding in the data plane.

Nexus on the other hand have a control plane each so in a lot of senses they are like independant switches. But there are addtional features such a vPC, HSRP active/active etc. to allow them to act as one logical switch.

What this means in practice is that in terms of redundancy when you ask about Nexus a certain amount of how it is done is down to you. For example from a L3 peering perspective my understanding is that with Nexus switches they are still seen as individual switches and so any redundancy is down to how you connect the L3 peers and Nexus switches support some and do not support certain L3 topologies.

Compare that with VSS where the pair are seen as one L3 peer to attached devices.

There is a configuration sync option with Nexus switches although i have no idea how well it works.

Perhaps Steve/Kevin can comment on that.

Jon

[Kevin Dorrell · Accepted solution]

Yes, I know about conf sync, and sometimes I wish I didn't. To be fair, it is a whole lot better than it used to be. Early versions were buggy, and sometimes would get into a state where the two boxes were synchronised but they thought they were inconsistent, but there was no way to sync them without blowing away the switch profile and starting over.

I started with conf sync so I am kind of stuck with it. If I was starting from scratch, knowing what I know now, I probably wouldn't use it. On the other hand, it does help enforce consistency, which is important if, like me, you have dual-homed FEXes.

Kevin Dorrell
Luxembourg



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[MOHAMMAD RAZA]

Thanks kevin and Jon