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New Member

Dot1q trunking over T-1

I have a predominately switched network centrally routed by an MSFC and have several buildings connected switch-to-switch over t-1 links(Pairgain campus T-1 w/ REX interface card). This works fine when passing only one vlan. However, I now have the need to pass 2, so I need to trunk (dot1q) - unless there is another way to pass more than 1 vlan. I can get the switches to trunk, but I can only pass frames with 1468 bytes of data or less. Anything over gets dropped. I believe this is due to the frame size of the t-1. When the dot1q packet exceeds the t-1's max, the frame is dropped. Apparently this 1468 byte limit is not big enough for the apps I need to run (I can't even log onto my win2000 network).

I'm trying to find a way to limit the frame size of the dot1q trunk. I have found other devices that I could use if I need to, but ideally I would like to use my existing equipment.

Any help, or suggestions would be greatly appreciated. Thanks.


Re: Dot1q trunking over T-1

Can you try changing the MTU size on both ends of the links ? You should be able to change this on interface basis .

New Member

Re: Dot1q trunking over T-1

I thought so too. Unless there's another way to do it, I can't set the mtu lower than 1500 bytes. The command is just "mtu ". 1500 is the minimum. And actually, I've got some newer 3550 EMI switches that I can't seem to set the interface mtu size at all.

Thanks for the reply though.

New Member

Re: Dot1q trunking over T-1

The point is that you need an MTU bigger than 1500

bytes on both sides of your T1 - specifically 1504

for the 802.1q trunks. This should be set on your

Pairgain equipment.

You cannot change MTU on an interface basis on the

3550, only for the switch as a whole, using the

"system mtu" command.