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I am connected to 3 layer switch used to create IP subnet-based VLANs. Is there any way to do VLAN hopping? Note that this isn't using 802.1q; it's not port-based L2.

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This can be easy as changing your IP address to one of the other subnets. Since you mentioned that this isn't port-based, then if there is no anti-spoofing rules on that switch you can do vlan hopping just like that. Try various gateways too, e.g. IP address from one LAN, and gateway from another. Sometimes works - on default setup with no filtering or routing policy this is the case on most switches.

You can see one vendor's implementation of subnet-based VLans and how they interact with the switch here starting on page 12: http://www.alliedtelesis.com/media/fount/how_to_note_alliedware_plus/overview_vlans.pdf

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i tried this but it did not work –  user1028 Aug 10 '12 at 9:48
    
i think if i spoofed an ip address, existed in my LAN, then the response packet will be forwarded by the 3 layer switch to that ip i spoofed. right ?! and this will happen due to the routing table in that 3 layer switch. what do u think about that?!!! –  user1028 Aug 10 '12 at 11:33
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