What is functional difference between VSS and VPC in Nexus ?

[wfqk]

Dear All, As we know Nexus is expensive, If we are just talking on VPC function in Nexus, what is functional difference between VSS and VPC ? If we use VSS, it could be installed in several Cisco devices, which are very cheaper.

[Reza Sharifi · Accepted solution]

These platforms are build for different environments. Nexus is mainly used for data center and VSS for campus environment. The max number of devices you can use for both VPC and VSS is 2.

As far as the difference, VSS has one control plane vs VPC 2 different ones. With VSS you eliminate the use of VRRP, HSRP, etc.. with VPC you still have to use one HSRP or VRRP.

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-6500-series-switches/white_paper_c11_589890.html

HTH

[wfqk]

Thank you for your reply. I think you are right. With STP, it looks like both VSS and VPC need it, but I do not think it is necessary for their own since both vss and vpc form its own channel, do you agree ? 

[Reza Sharifi]

Even with VSS, you still need to configure STP just in case you need it..

HTH

[wfqk]

Thank you so much for your excellent explanation !

[sean_evershed]

I would like to raise one additional point concerning vPC. With a double sided vPC topology the maximum number of switches is 4 rather than 2.

VSS does not have a similar feature for combining 4 switches. See this link for details:

https://learningnetwork.cisco.com/docs/DOC-23972

[akhilkamalakaran]

helpful

[Grant-Security/Network Analyst]

How on earth do you eliminate HSRP?  No VSS doesn't remove the need to HSRP.

[Joseph W. Doherty]

"How on earth do you eliminate HSRP?"

Because the VSS pair both support the same IP (SVI or port-channel interface).  (BTW, also much like Cisco's stackable 3750 and later switches don't often need a FHRP.)

"No VSS doesn't remove the need to HSRP."

Yes, it often does, as the VSS pair provides the redundancy that a FHRP, like HSRP, does between two logically different devices.

Do you use HSRP on one single device?  With VSS you have one logical device.

That said, yea you could run HSRP between two VSS pairs, but why would you?  (Actually I've configured/used HSRP on a "single" device but for purposes beyond first hop redundancy.)

[anoop verma]

Just want to add;

vPC:- Control messages are carried by CFS over Peer Link and a Peer keepalive link is used to check heartbeats and detect dual-active condition;

VSS:- Control messages and Data frames flow between active and standby via VSL;

[Joseph W. Doherty]

The big functional difference, VSS behaves as one logical device (although it avoids moving traffic ti/from its peer) while VPC operates as two logical devices except for the VPC port-channel. Further, VSS, has IAs on 6xxxx platforms (I recall the technology is being dropped), and VPC offers fabric extensions devices.

Functionally, Nexus series have feature of more interest/need to large scale data centers, while VSS platforms tend to be more generic.

Performance wise, the Nexus series generally can provide more bandwidth capacity than the VSS platforms. The capacity capability is probably the principle reason the Nexus series can be more expensive, but I recall they are not so much more expensive in the lower end Nexus series.