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

You cant plug a 2950 into a fex port.

--- On Sat, 5/29/10, Matt Bentley <mattdbentley_at_gmail.com> wrote:

From: Matt Bentley <mattdbentley_at_gmail.com>
Subject: Dual Homed Nexus 2Ks, 2950 on FEX HIF, and Spanning-Tree
To: "Cisco certification" <ccielab_at_groupstudy.com>
Date: Saturday, May 29, 2010, 10:35 AM

*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/C07-57282
9-01_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=61093138BE6B928721E
471BF442AA85D.node0
*<https://supportforums.cisco.com/message/469676;jsessionid=61093138BE6B92872
1E471BF442AA85D.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 - 11:25:37 ART