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How do I setup a single "trunk" port on a 3com Officeconnect 3CDSG8?

PaulELS
PaulELS asked
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I'm attempting to set up a trunk port between a 3com Officeconnect 3CDSG8 and my upstream provider that passes traffic across two VLANs. Unfortunately, the 3com only allows web configuration and when attempting to setup a trunk within the interface, it requires two ports or more ports to set up a trunk.

I want to use just one physical port to pass traffic between our router and the upstream provider. How do I go about setting this up?
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Top Expert 2010

Commented:
Two primary purposes for trunks is to create fault-tolerance and increase bandwidth.  You can create multiple links between devices that work as one virtual, aggregate link. A port trunk offers a dramatic increase in bandwidth for network segments where bottlenecks exist, as well as providing a fault-tolerant link between two devices.  To increase bandwidth and establish fault-tolerance, you have to have more than one physical port involved.  I've attached a doc that walks you through configuring the trunks and I don't see any indication that only one physical port is allowed, but I may missed something.

Theoretically, I don't think it's possible.
Top Expert 2010

Commented:
Forgot the doc, sorry.
TrunkConfig-3CDSG8.pdf

Author

Commented:
I'm not interested in fault tolerance, simply "trunking" the vlans. Upstream doesn't provide multiple physical ports to trunk with.

I want vlan traffic to pass seamlessly between upstream and local network through this device. My first guess was to configure a port that is a member of both vlans, pass tagged traffic only, and set the primary vlan to "none" but this doesn't appear to work.
Top Expert 2010

Commented:
I understand.  I was merely defining the purpose of setting up trunks.

Either way, I was wonder why you were looking at configuring a trunk and understanding your original attempts failed to establish VLANs provided great clarification.

Anyway, not trying to insult you here, but I've included the manual for the 3CDSG8.  Perhaps it sheds some light in setting up VLANs and possibly why they aren't working.  I setup a couple of VLANs for a sonicwall corporate/guest wireless network and it was a pain.  What doesn't work with your VLAN configuration?
Manual-3CDSG8.pdf

Author

Commented:
Thanks, unfortunately the manual hasn't been much help. It has contradicted the actual behavior of the switch and 3com support has acknowledged the same. For instance, it says that setting up one port as a trunk port is possible, however the web interface is hardcoded to prevent this from happening.

Currently, upstream connection is provided by creating a trunked pair of ports, where only one port is actually connected to the upstream. So I've defined T1 as ports 1 and 2, but only port 1 is connected.

This works, but is undesired. What I'd like to do is instead, set up only one physical port on the 3com.

To do this, I've attempted to setup a single port as a member of both vlans (1 and 100), configured the port to tagged only, and set the PVID to None.

Swapping out the connection from port 1 to port 3 (as defined above) causes a loss of connectivity.
Top Expert 2010
Commented:
Wouldn't you need to make port 3 a member of VLAN1 untagged and VLAN 100 tagged?  If the packet type is configured for tagged, then all untagged packets will be dropped.  PCs on VLAN1 will be untagged so this would create problems, right?

Author

Commented:
Solution was to leave as a standard port, untagged, making port 3 a member of vlan 100 and vlan 1.

Thanks!
Top Expert 2010

Commented:
I'm glad I could help and thanks for the points!