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The Cisco switch must have all disabled switch ports assigned to an unused VLAN.


Overview

Finding ID Version Rule ID IA Controls Severity
V-220667 CISC-L2-000210 SV-220667r539671_rule Medium
Description
It is possible that a disabled port that is assigned to a user or management VLAN becomes enabled by accident or by an attacker and as a result gains access to that VLAN as a member.
STIG Date
Cisco IOS XE Switch L2S Security Technical Implementation Guide 2021-09-09

Details

Check Text ( C-22382r507549_chk )
Step 1: Review the switch configurations and examine all access switch ports. Each access switch port not in use should have membership to an inactive VLAN.

interface GigabitEthernet0/0
switchport access vlan 999
shutdown
!
interface GigabitEthernet0/1
switchport access vlan 999
shutdown



interface GigabitEthernet0/9
switchport access vlan 999
shutdown

Step 2: Verify that traffic from the inactive VLAN is not allowed on any trunk links as shown in the example below:

interface GigabitEthernet1/1
switchport trunk allowed vlan 1-998,1000-4094
switchport trunk encapsulation dot1q
switchport mode trunk

Note: Switch ports configured for 802.1x are exempt from this requirement.

If there are any access switch ports not in use and not in an inactive VLAN, this is a finding.
Fix Text (F-22371r507550_fix)
Assign all switch ports not in use to an inactive VLAN.

Step 1: Assign the disabled interfaces to an inactive VLAN.

SW3(config)#int range g0/0 – 9
SW3(config-if-range)# switchport access vlan 999

Step 2: Configure trunk links to not allow traffic from the inactive VLAN.

SW3(config)#int g1/1
SW3(config-if)#switchport trunk allowed vlan except 999