Do Not Allow Negotiations
The preceding example prevents a user from negotiating a trunk with the switch, maliciously, and then having full access to each of the VLANs by using custom software on the computer that can both send and receive dot1q tagged frames. A user with a trunk established could perform “VLAN hopping” to any VLAN he desired by just tagging frames with the VLAN of choice. Other malicious tricks could be done, as well, but forcing the port to an access port with no negotiation removes this risk.
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