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Oct 25 / Greg

VLAN 1002 – 1005 Unusable In Cisco Switches

I was recently working with a WISP doing some network upgrades, when I hit an issue I hadn’t stumbled upon before. Their previous engineer had set them up on VLANs 1001, 1002, 1003, and 1004. I tried swapping them over to using a Cisco 4948(which is a great switch) in their core, but as it turns out only VLAN 1001 would work. After doing some quick research I see the following when I do a “show vlan”:

1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup

I’ve seen these show up a million times before, but I never bothered looking too close. It’s obvious from the VLAN names that they are old legacy token ring and FDDI VLANs, which who cares, right? The part I missed was act/unsup. The “unsp” stands for unsupported. This means that these VLANs are completely unusable no matter what you do. I’m not sure if this holds true for every Cisco switch, but it appears to be the case for the majority of the catalyst line.

So, for compatibility’s sake, you may want to avoid those VLANs in your network, even if you aren’t using Cisco kit.

Good luck and happy switching.

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