The Arista MLS layer 2 switch must not have any switch ports assigned to the native VLAN.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-255986	ARST-L2-000230	SV-255986r882300_rule		Low

Description
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.

Description

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.

STIG	Date
Arista MLS EOS 4.2x L2S Security Technical Implementation Guide	2023-01-11

Details

Check Text ( C-59662r882298_chk )
Review the configuration for all trunking ports to determine the native VLAN by using the following example (for vlan 1000): switch(config-if-Et4)#sh run int eth4 interface Ethernet4 description STIG Disable_VLAN 1 and native vlan to 1000 switchport trunk native vlan 1000 switchport trunk allowed vlan 2-999,1001-4094 switch(config-if-Et4)# Review the configuration to ensure no access switch ports are configured in the native VLAN by using the following example (for vlan 1000): swtich#sh vlan brief VLAN Name Status Ports ----- -------------------------------- --------- ------------------------------- 1 default 8 VLAN0008 active Cpu 25 VLAN0025 active Cpu 100 VLAN0100 active Cpu 1000 VLAN1000 active 4090 VLAN4090 active If any access switch ports have been assigned to the same VLAN ID as the native VLAN, this is a finding.

Check Text ( C-59662r882298_chk )

Review the configuration for all trunking ports to determine the native VLAN by using the following example (for vlan 1000):

switch(config-if-Et4)#sh run int eth4
interface Ethernet4
description STIG Disable_VLAN 1 and native vlan to 1000
switchport trunk native vlan 1000
switchport trunk allowed vlan 2-999,1001-4094
switch(config-if-Et4)#

Review the configuration to ensure no access switch ports are configured in the native VLAN by using the following example (for vlan 1000):

swtich#sh vlan brief
VLAN Name Status Ports
----- -------------------------------- --------- -------------------------------
1 default
8 VLAN0008 active Cpu
25 VLAN0025 active Cpu
100 VLAN0100 active Cpu
1000 VLAN1000 active
4090 VLAN4090 active

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

Fix Text (F-59605r882299_fix)
Configure the Arista MLS switch to ensure all access switch ports use a VLAN other than the native VLAN. Configure all access switch ports to a VLAN other than the designated native VLAN by using the following example: switch(config)#interface Ethernet 21 switch(config-Eth21)# switchport access vlan xxxx