Configuring vPC to support highly-available hosts

[stuartkendrick]

Is there a design pattern document for implementing back-to-back vPC in a Data Center, in support of highly-available hosts?

i.e. a design in which the core / Layer 3 switches use vPC to speak LACP down to the top-of-rack access / Layer 2 switches. And the access / Layer 2 switches then use vPC to speak LACP down to servers equipped with dual NICs

Currently, I am ending up with STP blocking VLANs on an access switch / Layer 2 uplink, and I figure there is a way to do better. Does one end up with a single vPC domain crossing both the core switches and the access-layer switches? Or does one deploy separate vPC domains for each pair of access-layer switches providing LACP to hosts?

See diagram for detail

--sk

Stuart Kendrick

[MHM Cisco World]

..

[sp2720401 · Accepted solution]

From that diagram STP is working as designed.

When you are using vPC you are essentially telling the upstream and downstream switches that the vPC pair is a single logical switch for all spanning tree decisions. When you combine vPC with LACP you are telling the upstream and downstream switches that spanning tree is only using a single link. The way you are configuring the connection is two individual links (PO201 and PO200) between single switches. Spanning tree can only have one active link per spanning tree instance between switches to avoid loops.

The whole purpose of vPC is so two switches appear as one switch and LACP is so multiple links look like one link. 

PO1 on dc201-esx and dc200-esx should also be in a vPC. 

On dc-a-rtr and dc-b-rtr you should also be doing a single vPC between them. Remove vPC/PO 201 and add all of the interfaces between the ESXI switches and RTR switches to either PO200/201 or a new PO/vPC combo.

[MHM Cisco World]

....

[stuartkendrick · Accepted solution]

OK, I understand now -- thank you for the explanation.

I have implemented your suggestions; and now of course STP is no longer blocking any ports.

I attach an updated diagram.  If you see ways to improve, do let me know

--sk