V-269971

Discussion

Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victim’s MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attacker’s VLAN ID (probably the well-known and omnipresent default VLAN) is stripped off by the switch, and the inner tag that will have the victim’s VLAN ID is used by the switch as the next hop and sent out the trunk port.

Check Content

Review the Dell OS10 Switch configurations and examine all access switch ports. Verify that they do not belong to the native VLAN of the trunk ports. The native VLAN on trunk ports is set by the switchport access vlan command on those ports. In the example below, the native VLAN is 99 and the access ports must be configured to other VLANs.

interface ethernet 1/1/1
 no shutdown
 switchport mode trunk
 switchport access vlan 99
 switchport trunk allowed vlan 2100-2102
!
interface ethernet1/1/2
 no shutdown
 switchport access vlan 201
 flowcontrol receive off
!
interface ethernet1/1/3
 no shutdown
 switchport access vlan 200
 flowcontrol receive off

If any access switch ports have been assigned to the same VLAN ID as the native VLAN, this is a finding.