Multi-layer vPC

[s-durando]

Hi,

you find attached my network architecture with 2 Nexus 7010 on core layer and 2 Nexus 5020 on distribution layer, each one with 1 N2148T fabric extender switch. PC-1 is connected to one N2148T, PC-2 is connected to the other N2148T.

PC-1 and PC-2 are on the same VLAN X.

When every link is up, PC-1 is able to ping PC-2.

If I shutdwon the Port-channel 10 between N5K-1 and N5K-2, PC-1 is no more able to ping PC-2. In the output of 'show spanning-tree vlan X' command issued on both Nexus 7010 I see Port-channel 11 moving from forwarding to blocking states and back to forwarding state every few seconds.

What's wrong on my architecture?

Regards

Stefano

[wil_amaya]

Hello.  Looks like you may have a spanning-tree loop.

Think about something like the following

:

On N7k1: Eth 1/10 - Po11, vpc 11

On N7k1: Eth 2/10 - Po12, vpc 12

On N7k2: Eth 1/10 - Po12, vpc 12

On N7k2: Eth 2/10 - Po11, vpc 11

On N5k1:Eth 1/33 and 1/34, vpc 11

On N5k2: Eth 1/22 and 1/34, vpc 12

Let me know how that works out.

[s-durando]

Hi wil_amaya,

I think that your solution shouldn't work because you are using different vPC IDs (11 and 12) on N5K which are vpc peers.

When you issue 'show vpc' command on N5K you see 'peer does not have corresponding vpc' warning message.

Any other suggestions?

Thanks a lot

Stefano

[wil_amaya]

Stefano, hello.   You would keep the same peer-link between your 5010s.   What that would allow you to do is allow you to provide vPC to downstream clients.  With the suggstions i made your 5010s become vPC clients of the 7010s.   I have used this design several times (double sided vPC) and it has worked for me.   The issue you spoke of earlier about your interfaces going from forwarding to blocking and back to forwarding  and then blocking again and so forth are indicative of a loop which is what i think you ahve done by using vPC 11 across the board.  Hope tha thelps.  I can send you sample diagrams of what I have done at client sites to give you some ideas.  If you want to please provide your email and i'll send over.  Thanks.

Wil

[s-durando]

Hi Wil,

I found a working solution by dual-homing N2Ks fex uplink to N5Ks (see the picture attached).

Thanks for your suggestions.

Stefano