Spanning tree problem

[Mober]

I currently have two Cisco Catalyst 3500's with both of there Gigabit ports used to connect them together. I have just found using a show spanning-tree command that my upstairs switch is forwarding traffic out of both ports, while the downstairs switch is forwarding out of one of the gigabit ports and not the other. Is there a way to allow both of the ports to be up and forwarding? If so will this require everyone to be off the network before performing this, or can I enable the interface during production?

 

[cisconooblet]

You could add them to a channel group and band both ports together as 1. Its called etherchannel. Its not true load balancing but it will use both links and balance somewhat.

Stp (as it should) prevents all 4 ports from being in fwd state as it would create a loop. Your upstairs switch has become the root switch and both ports will settle into a fwd state. The other switch will only have 1 fwding port to the other switch at any given time. The blk'd port is for a failed link.


Not sure if this will bring down the link between the switches though. I'm thinking not, but some have issues doing it and end up having to take down the interfaces and then right back up to get the channel to come up fully. Maybe someone else can give some more info on this.

There may be other options but this is the only I know of.

 

[vipergg]

Spanning tree is doing its just and elimnating a loop . the only way around this is to make those links a etherchannel which bundles both links into one spanning tree instance.

 

[Mober]

Thanks that does explain alot of things.