Comments on: BCMSN: VLAN Configuration and Implementation

By: dave cowley

dave cowley — Mon, 26 Apr 2010 11:59:49 +0000

Nice site – just came across it looking for a breakdown of a DTP Packet (going to look to see if you have one after….) google took me to your image break out of a dotq tag. I think there is slight type-0 – the protocol type (0×8100) should be located in the TPID (tag protocol ID) filed instead of the tag control info (TCI) field in the lower two bytes…. if ‘m not mistaken (would not be the first).

Dave Cowley

By: Wassim

Wassim — Tue, 08 Dec 2009 06:51:47 +0000

quote: “ISL is sometimes referred to as double tagging.”
To avoid confusion, there’s also the double tagging attack against switches. This is where an attacker forges a frame with two VLAN tags: the external VLAN tag corresponds with the native VLAN on the switch trunk, and the interior VLAN tag corresponds with the target access VLAN.

By: Aragoen Celtdra

Aragoen Celtdra — Wed, 22 Apr 2009 22:23:45 +0000

Thanks for pointing that out. I think you are right about the lower-end switches. You’ve prompted me to go ahead and test it out on my lab.

I should’ve put a blurb that the exception on the reserved vlans (1006 – 1024) apply to Catalyst 4500 and 6500 family of switches. Unfortunately, I can’t lab this out since I don’t own these higher-end switches. I should practice on our production switch… Nah!

By: invalidCCIE

invalidCCIE — Wed, 22 Apr 2009 20:32:17 +0000

i’ve succesfuly created vlans in range 1005..1024 on c2950, 2960 and 3560:

Switch(config)#vlan 1006,1007-1024
Switch(config-vlan)#exi
Switch(config)#^Z
Switch#sh vla br | in 10
1002 fddi-default act/unsup

1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
1006 VLAN1006 active

1024 VLAN1024 active

so i don’t think these vlans are some special.