I help administer an older network with cisco 3620 routers and 5509/5505 Catalyst switches. They are using isl for trunking between the routers and switches and .1q between the core switch and other switches. Now the IOS's won't support isl. Is there a way to transition from isl to .1q without taking the network down and doing it all at one time?
What I believe there is no way to not migrate from ISL to dot1Q w/o disconnect the connecting user. It was because when you remove the ISL, the trunk will down and all VLAN removed from this port. Then enable dot1Q and add the VLAN back to the trunk.
Moroever, I suggest never do such move & change during office hour. It is better to arrange maintenance window.
Hope this helps.
Theres no way you can change your trunking protocol from ISL to DOT1Q without having a down time. Just make the required changes after scheduling a downtime. However, in my opinion it should'nt take too long. An hour or two should be more than enough to change all your trunks from ISL to DOT1Q and also make sure things are working fine. You need to make sure that everything is working fine after the changes and that would take more time than the time required to make the changes!
Also keep the original configs ready in case things don't work out fine and you need to revert to your original configuration.
Hope this helps!
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