Trunking between a Cisco Catalyst and a 3Com SuperStack

Trunking between this equipments is problematic at best, the meaning of trunk in the 3com is not the same as in the Catalyst, also the vlan methods are not the same either.

Trunk in the 3Com SuperStack is port aggregation between two 3Com devices, whether in the Cisco is really a downlink trunk, luckily both devices speak 802.1q so the trunk configuration shouldn’t be a big problem.

First of all we need to establish the trunk port between the Catalyst and the SuperStack, so we’ll start by defining the port in the Catalyst.

Some considerations on this config. It’s always recommended by Cisco and security-wise to use another vlan than vlan 1 for trunking, that’s what we’re doing here, also we’re restricting which vlans we will accept and retransmited to the 3Com switch.

There’s a huge implementation difference between the trunking trunking transmission between Cisco and 3Com, the 3Com switches tag all the vlans by default, but the Cisco switch won’t tag the trunk vlan, this is a really annoying factor that made me waste some hours!

The trick resides in adding all the vlans tagged into the port that you’re using as a trunk, you don’t really need to add the trunking vlan that you configured back on the cisco, it doesn’t work that way. So let’s add one by one all the vlans in the trunk port. In order to do that we need to use the bridge menu in the 3com switch.

Repeat this in the trunk port for each vlan you’re adding in the Cisco trunk side. When you have your trunk port configured properly (also be careful with duplex and speed configs) you just need to add the ports into the vlan untagged. So let’s say we want to add port 1 to the vlan 10.

As soon as that’s done the port will be talking head to head with all the other ports in vlan 10 also in the Cisco switch.

The difficult thing is making the 3Com switch accesible through an IP address, since the 3Com switch will only publish its public IP address though VLAN 1, this one is a though cookie.

7 thoughts on “Trunking between a Cisco Catalyst and a 3Com SuperStack

  1. Mr: lynxman

    Supossed that be needed to uses VLAN1 both Cisco and 3Com, how i can configura boths equipments (2950 Cisco and 3226 3Com).

    Regards

    Eduardo

  2. lynxman says:

    Using the VLAN 1 is a security danger, you’re always safer not using it.
    On the other hand, you just need to use it as you would use any other VLAN for the trunking, just add the trunking port to vlan 1 TAGGED and then add the rest of the ports as you would do normally but untagged, that’ll work.

  3. Mian says:

    I have 3com switch(10…network)& attch thorough fiber 4500 cisco(192..network)& want all users pin each other & use internet thorough cisco network router.

  4. I know this is kinda old, but i’m this exact problem:

    “The difficult thing is making the 3Com switch accesible through an IP address, since the 3Com switch will only publish its public IP address though VLAN 1, this one is a though cookie.”

    Did you find any solutions for this? Because every other device in my network is working in VLAN 900, and this 3com thing is driving me nuts.

    • lynxman says:

      Actually there’s no real solution for managing it remotely once you move your trunking VLAN to a different one since the hardware won’t support it, the only way I got access was connecting through a server sitting next to the switch with a serial cable.

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