Splitting RSTP

[r.roudi]

I'd like suggestions from community peers regarding a design.

There are a couple of hard requirements: 

1) Core switch has to run RSTP (no PVST, no MST)

2) A Port-Channel links Distribution to Core. The Port-Channel on the Core has to be switchport and use a /30 SVI.

I want the Core to be the STP root for its own VLANs. Each Distribution switch be the root for VLANs in that building. 

The only problem here is the single common VLAN between Core and Distribution will cause a "leak", for lack of better term. 

One solution I can think of is the Port-Channel on Distribution configured with an IP. Basically a routed port, no SVI or VLAN on Distribution side of the Port-Channel. I haven't tried that before (one side of a Port-Channel using SVI and the other side routed). My guess is it should work.

Another is configuring ACL to filter out STP on the Port-Channel. Although I want to avoid ACL if possible.

[Jon Marshall]

I have never done it with etherchannel but with individual links what you are proposing works fine.

Used to be the only way to have a routed link between a 6500 running CatOS and a L3 device such as a router.

So I can't see why it wouldn't work. Obviously L2 protocols will still be sent on the etherchannel from the core switch end but as you say you are not extending a vlan between the distribution and core which is what you want.

Jon