Re: Dual Homed Nexus 2Ks, 2950 on FEX HIF, and Spanning-Tree

Nexus 2ks do not support switches below them. Only hosts that do not
run spanning-tree.

-nick

On Sat, May 29, 2010 at 11:35 AM, Matt Bentley <mattdbentley_at_gmail.com> wrote:
> *Hi Group:*
> *
> *
> *I have a question about running spanning-tree on the Nexus switches.*
> *
> *
> *Basically, I am trying to get working a setup similar to this one (see page
> 27 of the PDF). The difference being that the HIF (FEX Downlink) port is
> plugged into a 2950 switch. No traffic is able to get to or from the 2950
> switch - because I believe of spanning-tree issues*
>
> *
> http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572829-01_Design_N5K_N2K_vPC_DG.pdf
> *<http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572829-01_Design_N5K_N2K_vPC_DG.pdf>
>
> *Per below, you see that the same FEX port E122/1/48 is showing up on both
> Nexus switches. However, it appears like the Nexus's are having
> spanning-tree problems (Dispute P2P). At this point, I think it's because
> both NX01 and NX02 are sending spanning-tree BPDUs to it. I thought that I
> could "unify" the control planes of these switches by putting e122/1/48 on
> both Nexus switches into the same port-channel - I guess this is with the
> assumption that the problem is caused by both Nexus switches sending BPDUs.*
>
> *However, when I attempt to do it, I get this error. *
>
> *NX-01(config-if)# interface Ethernet122/1/48*
> *NX-01(config-if)# channel-group 267 mode active *
> *Fabric in Fex A-A mode, can't configure sat port as member*
>
> *After researching, it appears like the Nexus will not allow HIF (FEX
> Downlink) ports to be placed in a port-channel when a FEX (in this case
> 2148) is dual-homed to two Nexus 5Ks. Most Cisco documentation uses
> different FEXs. *
>
> *
> https://supportforums.cisco.com/message/469676;jsessionid=61093138BE6B928721E471BF442AA85D.node0
> *<https://supportforums.cisco.com/message/469676;jsessionid=61093138BE6B928721E471BF442AA85D.node0>
> *That's my understanding also, you can only do port channels to the host
> when you use a single connection from two different single homed FEX's
> (using vPC).*
> *
> *
> *I've read a few things about spanning-tree bridge assurance, but was
> curious if anyone had encountered this before. Any comments would be most
> helpful. Thank-you.*
> *
> *
> *NX-01# show spanning-tree vlan 27*
> *VLAN0027*
> * Spanning tree enabled protocol rstp*
> * Root ID Priority 8219*
> * Address 0000.0000.0000*
> * Cost 3*
> * Port 4128 (port-channel33)*
> * Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec*
> *
> *
> * Bridge ID Priority 32795 (priority 32768 sys-id-ext 27)*
> * Address 0000.0000.0000*
> * Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec*
> *
> *
> *Interface Role Sts Cost Prio.Nbr Type*
> *---------------- ---- --- --------- --------
> --------------------------------*
> *Po33 Root FWD 1 128.4128 (vPC peer-link) Network P2p *
> *Eth1/1 Altn BLK 2 128.129 P2p *
> *Eth1/2 Altn BLK 2 128.130 P2p *
> *Eth1/3 Desg FWD 4 128.131 P2p *
> *Eth1/4 Desg FWD 4 128.132 P2p *
> *Eth1/14 Desg FWD 4 128.142 P2p *
> *Eth120/1/26 Desg FWD 1 128.3098 (vPC) Edge P2p *
> *Eth121/1/18 Desg FWD 1 128.3218 (vPC) Edge P2p *
> *Eth122/1/48 Desg BLK 1 128.3376 (vPC) P2p *
> *
> *
> *
> *
> *
> *
> *NX-02# sh spanning-tree vlan 27*
> *VLAN0027*
> * Spanning tree enabled protocol rstp*
> * Root ID Priority 8219*
> * Address 0000.0000.0000*
> * Cost 2*
> * Port 129 (Ethernet1/1)*
> * Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec*
> * Bridge ID Priority 32795 (priority 32768 sys-id-ext 27)*
> * Address 0000.0000.0000*
> * Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec*
> *Interface Role Sts Cost Prio.Nbr Type*
> *---------------- ---- --- --------- --------
> --------------------------------*
> *Po33 Desg FWD 1 128.4128 (vPC peer-link) Network P2p *
> *Eth1/1 Root FWD 2 128.129 P2p *
> *Eth1/2 Altn BLK 2 128.130 P2p *
> *Eth1/3 Desg FWD 4 128.131 P2p *
> *Eth1/4 Desg FWD 4 128.132 P2p *
> *Eth1/14 Desg FWD 4 128.142 P2p *
> *Eth120/1/26 Desg FWD 1 128.3098 (vPC) Edge P2p *
> *Eth121/1/18 Desg FWD 1 128.3218 (vPC) Edge P2p *
> *Eth122/1/48 Desg BLK 1 128.3376 (vPC) Dispute P2p *
>
>
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Received on Sat May 29 2010 - 12:25:51 ART