Sizing vPC Peer Link

[ecornwell]

Hello,

I'm looking at setting up a set of 3524x's in a vPC domain.  I've seen a lot of recommendations and they usually involve a pair of 10G links.  From what I've read/understand, there shouldn't be a lot of traffic on these links during normal operation.  Is there any kind of sizing recommendations?

Thanks!

[Francesco Molino · Accepted solution]

Hi

You're right there shouldn't be a lot of unicast traffic unless vpc member ports go down on 1 member.
It's also used to replicate multicast steam and do all sync between the 2 boxes.

In terms of recommendation, vpc peer link won't work on 1G links and Cisco says that you must have 2 x 10G links.
Here 1 of multiple documentation available as vpc best practices:
https://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/sw/design/vpc_design/vpc_best_practices_design_guide.pdf

[Joseph W. Doherty · Accepted solution]

Normally, you shouldn't see any significant traffic on that link, except in case of other hardware failure that makes the peer link the backup/alternative path. As such, if you look at your hardware, and consider worst case for traffic that might be shifted, you could size your peer link capacity accordingly.

[ecornwell]

Thank you both for your replies! 

Looks like I shouldn't need to go larger than 2x10G connections.

Thanks!

[Francesco Molino]

You're welcome

[Joseph W. Doherty]

Probably not, but, again, you need to consider possible hardware failures. For example, might a whole line card failure push you above 20G?