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When do i implement ISL and 802.1q trunking for PVST??

I have a general question on the above. I understand that ISL trunking supports a spanning tree for each VLAN in a PSVT environment, only if it on point-to-point. If i have a Vlan with cisco switches and other vlan using non-cisco switches that resides on a separate Vlan, can i configure my trunk ports to ISL on these separate Vlan?? Can I use 802.1q instead?? In wat situation can i configure my trunk port to type 802.1q?

Lawrence

3 REPLIES

Re: When do i implement ISL and 802.1q trunking for PVST??

ISL is Cisco proprietary, 802.1q is the standard. In your case you will need to use 802.1q since you are going from Cisco to non-Cisco.

New Member

Re: When do i implement ISL and 802.1q trunking for PVST??

You can use both on the same network. The trunk links and the encapsulation they use are only significant between the two switches. For example, let's say you have 3 switches; A, B and C. Switches A and B are Cisco switches and C is 3Com. A and B are connected to each other and B and C are connected to each other. You can use ISL on the trunk between A and B and 802.1q on the link between B and C. I have actually set this scenario up between three Cisco switches when I was practicing configuring trunk links, and used both encapsulation methods on the same Cisco switch.

So, I guess the point I'm trying to get across is, the trunk's encapsulation method is interface specific, not VLAN specific. I hope I have helped.

New Member

Re: When do i implement ISL and 802.1q trunking for PVST??

Thanks for yr help. I am more clear now.

rgds

Lawrence

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