Connection problem between 3Com and Cisco

[bkesting]

Hello,

I have a network that has a 3Com SuperStack 3300 XM switch in use. I have a Cisco Catalyst 3524-XL switch that I am trying to add to it. I have setup a trunk port on each switch, but when I hook the Cisco switch up, all network traffic seems to die........even though I do not have any devices directly connected to the Cisco switch.

Could the problem be a Spanning-Tree problem? I have Spanning-Tree and port fast enabled on all of the ports of the switch and the trunk port of the 3Com switch. Do I need to run spanning-tree over the trunk?

Thanks.

 

[mtashiro]

You should spanning-tree enabled on the trunk ports. You are using Dot1q trunks correct?

 

[bkesting]

I am using dot1q on the Cisco switch. Not sure what the 3Com switch is using. Do I need to use port fast on the trunks?

 

[baddos]

Make sure that the port on the cisco is setup as a trunk.

I.E.
configure terminal
interface fastethernet0/1
switchport mode trunk
end

Also make sure that the port on the 3Com is setup with the 802.1q VLAN tagged. 3Com does a really weird way of configuring switch trunks. Basically you need to goto the VLAN configuration tab on the webinterface and add all the vlans on the port.

 

[bkesting]

Okay, I will try that. I need to add 802.1q tagging to the trunked ports on both devices right?

Also, if I am using Spanning-Tree on the trunked ports, do I need to enable portfast(on the Cisco switch) and FastIP(on the 3Com switch)?

 

[baddos]

If you have spanning-tree enabled on the 3com, then don't use portfast on the Cisco. W/ the 3Com spanning-tree is either on or off, you can't specify specific ports like you can on the Cisco.

 

[bkesting]

I have the 3Com and Cisco switches connected now and they work great. Do I need to have more than 1 trunk line? If I try to add a second trunk for redundacy, all network traffic dies. Any thoughts?

 

[baddos]

If you want, make an "port group" (etherchannel) on the Cisco switch and a "port trunk" on the 3com switch. This will take 2 or more ports and bind them together. The reason all traffic stops is because you created a loop in your network and had spanning-tree disabled on one or all the switches.

-Bad Dos

 

[bkesting]

I have spanning tree enabled on both switches.............i will have to try the etherchannel option.

Thanks.