C2960S multiple uplinks

[avilt]

I have a simple lab setup, 2 new C2960S switches, no vlans, with trunked on 2 ports Gi1/0/47 and Gi1/0/48 for redundency.

Now the port Gi1/0/48 on non-root bridge will turn amber as expected.

SW1<----- 2 cables----> SW2

Now I have created many vlans on both the switches, hard coded 2 ports Gi1/0/47 and Gi1/0/48 on both switches as trunk. Now LED for Gi1/0/47 and Gi1/0/48 on both switches turn green. What is the resaon? The show spantree output seems to be normal as shown below

Root-Bridge#

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------
Gi1/0/47            Desg FWD 4         128.47   P2p
Gi1/0/48            Desg FWD 4         128.48   P2p

Non-Root-Bridge#

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- ---------
Gi1/0/47            Root FWD 4       128.47   P2p
Gi1/0/48            Altn BLK 4         128.48   P2p

[Tarquin Joseph]

Is there a specific requirement for spanning tree? Why not use LAG instead? Can increase bandwidth between switches in normal operation but still maintain redudancy.

In any event, you mention that port gi1/0/48 on the none root bridge turns amber in your first paragraph, then mention that all ports are green. Which is it?

Also, what version of spanning tree are you using on the switches?

[Leo Laohoo]

I agree.  Why not use EtherChannel.  Nice and simple.

[avilt]

Whats is LAG?

Can I use etherchannel with LAN cables (cat 5e) as well?

[Leo Laohoo]

LAG = Link AGgregation or EtherChannel

Can I use etherchannel with LAN cables (cat 5e) as well?

Yes.

[andtoth · Accepted solution]

Hi,

This is a normal and expected behavior. As the Cisco switches are running per-vlan spanning-tree (PVST), each vlan is a separate instance and a trunk port carries multiple vlans so it won't turn amber because there might be other vlans which are in forwarding state.

When an access port is in STP blocking state, the port LED is amber.

When a trunk port is in STP blocking mode, the port LED is green.

Please see the following discussion for more details:

https://supportforums.cisco.com/thread/2053684

Best regards,

Andras

[avilt]

Thank you for the link.

But I dont think it has got anything to do with PVST. On non-root bridge the command  show spanning tree lists the port Gi1/0/48 as blocked for all the vlan's.

[andtoth]

I understand your concern but the trunk port will stay green even if all vlans are in blocking mode on it. This is a decision made by the developers of the switch, mainly due to the fact that with PVST, some vlans might be blocking, some might not. Therefore it'd be confusing if the trunk port would be amber.

Andras