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New Member

802.1q trunk on a Shared Medium

I read where the 802.1q standard allows trunks to be put on a shared medium. I have always setup trunks in a point-to-point to configuration but we have a need to setup a single trunk between 3 or more devices.

The Config we are considering resembles the diagram below:


| |====2924

| h |

2924====| u |

| b |

|__ |====2924

==== is a 802.1q trunk

All the switches will have the same VLANs on them.

Will this trunk work,


New Member

Re: 802.1q trunk on a Shared Medium

The diagram got scrambled in the post.

The configuration we are looking at emulates several trunks from 2900 switches connected together with a single hub.

sorry for the mess.



Re: 802.1q trunk on a Shared Medium


Trunks in your setup would be point to point still, but you would have two switches connected to a central "hub" switch via trunks. So, yes this works fine and it would allow all VLANs to exist on all switches. Hope this helps you.


Re: 802.1q trunk on a Shared Medium

Is my understanding correct you want to connect several switches via a multiport repeater and configure 802.1q trunk ports on the switches?

I've never used trunks this way and never read about trunks on shared media (could you provide the link?).

But accordig to no trunk negotiation on Cat2900s it might work. Just be careful with native VLAN (it has to be the same on all "shared" trunk ports) and VTP domain (again, it has to be the same).



New Member

Re: 802.1q trunk on a Shared Medium

No reason why not at all. Just ensure the duplex noegotiates to half, or set it manually. There is nothing in 802.1q to suggest that all trunks must be full-duplex point-to-point.

I remember attending a 3Com CoreBuilder 9000 course some years ago when this topology was described - it provoked heated discussion especially from the Cisco-centric attendees.


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