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New Member

ISL and 802.1q

All of our current LAN switches, most are catalyst 3500 series are running the ISL trunking protocol for our VLAN and we are looking to introduce a Catalyst 2950G as a server switch and of course this does not support ISL. We have a 3500XL that host all our fiber connections out to the other LAN switches, Is there an easy way to set the ISL interfaces to 802.1q without losing our current VLAN config information


Re: ISL and 802.1q

You shouldn't lose any vlan configs as ISL and dot1q are trunking encapsulation protocols . If the 2950 is connecting back to the 3500XL then you can just make the one link to the 2950 a dot1q trunk and leave the rest alone , not ideal but it should work ok . You don't have to change all the trunk links just because you have to connect in a 2950 that runs dot1q.

New Member

Re: ISL and 802.1q

Hi, Thats true 2950 does not support ISL but when u connect it with 3550 then u just need to define trunk encapsulation dot1q on one of cisco interface of 3550. For example: 2950's port number gi0/1 is connected to 3550's gi0/1 then u just need to define both gi0/1 as trunk port & on gi0/1 of 3550 u need to put the trunk encapsulation as dot1q thats it. It will not affect ur current config.

Hope it will help you. If u need anything dont hesitate to ask.



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