Trunking To A Nexus Switch
40 10Gb ports, of which 16 can run in 1Gb mode. Dual PSU with 5 fans.
I’m using a Nexus 5020, and attempting to trunk a 7606 running service provider code…but for some reason VLANs aren’t passing.
I issue the following on the 7606:
1 2 3 4 5 6 7 8 9 10 11 12 13 | 7606#show int te1/1 trunk Port Mode Encapsulation Status Native vlan Te1/1 on 802.1q trunking 1 Port Vlans allowed on trunk Te1/1 1650-1699 Port Vlans allowed and active in management domain Te1/1 1650-1653 Port Vlans in spanning tree forwarding state and not pruned Te1/1 1650-1653 |
This tells me everything is passing here…what happens when I do the same on the Nexus side:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | Nexus5020# show int e1/17 trunk
--------------------------------------------------------------------------------
Port Native Status Port
Vlan Channel
--------------------------------------------------------------------------------
Eth1/17 1 trunking --
--------------------------------------------------------------------------------
Port Vlans Allowed on Trunk
--------------------------------------------------------------------------------
Eth1/17 1,1650-1699
--------------------------------------------------------------------------------
Port Vlans Err-disabled on Trunk
--------------------------------------------------------------------------------
Eth1/17 none
--------------------------------------------------------------------------------
Port STP Forwarding
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Port Vlans in spanning tree forwarding state and not pruned
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Port Vlans Forwarding on FabricPath
--------------------------------------------------------------------------------
Eth1/17 none |
As you can see above, none of the VLANs are “STP Forwarding”…but what could be the problem?
It turns out that Nexus chassis have a new feature called Bridge Assurance. It is an enhancement that helps protect against unidirectional link failure. Any port designated as “spanning-tree port type network” has it enabled by default. It expects that the switch on the other end supports the feature and is sending crafted BPDUs over to you. If you happen to be trunking to a standard catalyst switch, then it basically blocks all VLANs from passing on the port! How do we work around it…by disabling it.
You have to globally disable the feature with:
1 | no spanning-tree bridge assurance |
.
Magically, your VLANs will begin passing:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | Nexus5020# show int e1/17 trunk
--------------------------------------------------------------------------------
Port Native Status Port
Vlan Channel
--------------------------------------------------------------------------------
Eth1/17 1 trunking --
--------------------------------------------------------------------------------
Port Vlans Allowed on Trunk
--------------------------------------------------------------------------------
Eth1/17 1,1650-1699
--------------------------------------------------------------------------------
Port Vlans Err-disabled on Trunk
--------------------------------------------------------------------------------
Eth1/17 none
--------------------------------------------------------------------------------
Port STP Forwarding
--------------------------------------------------------------------------------
Eth1/17 1,1650-1653
--------------------------------------------------------------------------------
Port Vlans in spanning tree forwarding state and not pruned
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Port Vlans Forwarding on FabricPath
--------------------------------------------------------------------------------
Eth1/17 none |
This seems to be a little documented feature and generally takes a little google-fu to find it. Good luck and happy switching my friends.
Good to see you posting again. That’s some serious Ferrari you have at the house.. 🙂 🙂
Are you going to be presenting in Miami this year?
@Tim
Indeed sir, I’m posting…for now 🙂 When life gets going, this is something I sacrifice. I was studying to recertify and I didn’t have a life for a few months there.
I wish I could afford to grab any gear for the house. I wish I could have someone send me cosmetically broken gear for free heh. I’m sure I could think of SOMETHING to do with it.