Difference between a Trunk and a Access port with only 1 VLAN

Patrick Sheridan · ‎01-24-2012

I was wondering what pros / cons would there be if you have only one VLAN that must be shared between two switches and there is the choice of making that connection a Trunk or and Access port. For this discussion there is only the two switches on the LAN and while there are multiple VLANs only one of them appears on both devices (VLAN 808) with multiple access ports on each. I don't think the type of switch makes a difference but if there is a difference then that would be interesting to hear about.

Switch 1

VLAN 808

VLAN 200

VLAN 100

Switch 2

VLAN 808

VLAN 555

VLAN 777

An obvious answer might be to say "Use a trunk because its between two switches and you always use a trunk between switches" but I am looking for a deeper description on how a Trunk would be of benefit over an Access port in this situation. Does it even really matter which one is used?

Security?

Processing effort involved for each frame?

Bandwidth differences between the two methods?

If this LAN was larger and with more devices i.e. other switches and routers, would that make a difference?

Other considerations?

Thanks.

Patrick

Peter Paluch · ‎01-24-2012

Hi Patrick,

If only a single VLAN is to be shared between two switches then there is really no reason to have the interconnection run as trunk (even if locked down to allow only this single VLAN). Functionally, an access port and a trunk port in this situation would behave identically. A trunk with all VLANs allowed would allow frames from all VLANs to be passed to the other switch, however, the opposite switch would drop the frames for which there is no VLAN created on it.

Running inter-switch links as trunks even in simpler topologies is a matter of best practices. First, as these are managed switches, they must have a management VLAN assigned, and it is appropriate for this VLAN to be a separate VLAN not used for any other purposes, especially not for user data traffic. This would immediately neccessitate running a trunk even in your situation, as you would want two VLANs to span the trunk: 808 and this management VLAN. In addition, future network extensions and enlargements may require adding new shared VLAN. If the interconnection was an access mode link, its reconfiguration to trunk would cause a transient network outage - something that may not be possible to do outside a maintenance window.

My two cents on this...

Best regards,

Peter

Patrick Sheridan · ‎01-24-2012

Thank you for taking the time to reply. From what you wrote, besides best practices and future expansion an access port and a trunk with one VLAN is pretty much the same thing. Thanks.

mgallagher44 · ‎04-19-2013

VTP packets will only be transmitted over trunk ports but I'm assuming you wouldn't have VTP running between the two switches if you only want one VLAN to pass between them.

Patrick Sheridan · ‎04-19-2013

This is a good point. Thanks for your answer.

blau grana · ‎04-21-2013

Hello Patrick,

trunk - frames will be sent with VLAN tag. If only one VLAN allowed, then only frames with allowed vlan tag will be sent

access - frames will be sent untagged

Best Regards

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