Cisco VPC technology application in Data Centers and...

[Borman Bravo]

I wanted to see what other network architects thought of Cisco's vPC technology which is available on the Nexus line of switches and its application. Personally I believe that under most circunstances vPC is strictly a Data Center technology, it should not be implemented in an user access or closet access scenario in which the more nowdays traditional "layer 3 to the closet" can be applied, with vPC to the closet we are taking advantage of all available bandwidth and the added redundancy but we are still creating an environment susceptible to layer 2 loops, on the other hand, the "layer 3 to the closet" can provide the same "use all available uplinks" results if used in conjunction with a routing protocol that will round robin traffic while at the same time isolating any potential layer 2 issues to a closet, any thoughts?

[Jon Marshall]

Yes, i would basically agree although it does presuppose that all non DC networks will be L3 routed from the access-layer which is not the case.

The problem in the DC has always been the flexiblity of L2 vs the scalability of L3. VSS and vPC are attempts to remove STP from the equation or at least demote it to a backup protocol rather than an active particpant in the L2 topology. With these technologies you can now full utilise the bandwidth from your L2 uplinks.

But VSS/vPC are just the start in the DC at the moment. It is a fast changing environment with the advent of fabricpath and vxlan which was discussed recently and allows L3 isolation at the edge while overcoming some of the issue with a traditional L3 setup.

L3 from the access-layer is a good solution in campus networks but it does have limitations ie. the ability to have a vlan scross multiple access-layer switches is lost and this can a restriction that can bite you later.

There of course other ways to achieve full use of uplinks as well has having L2 uplinks ie. run L2 uplinks from an access-layer switch to a pair of distro switches and then interconnect the distro switch with a L3 uplink. This does not restrict you in the way a L3 routed access-layer does.

Jon