VLAN 1 must not be used for user VLANs.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-3971	NET-VLAN-004	SV-3971r2_rule	DCCS-1	Medium

Description
In a VLAN-based network, switches use VLAN 1 as the default VLAN for in-band management and to communicate with other networking devices using Spanning-Tree Protocol (STP), Cisco Discovery Protocol (CDP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP)--all untagged traffic. As a consequence, VLAN 1 may unwisely span the entire network if not appropriately pruned. If its scope is large enough, the risk of compromise can increase significantly.

Description

In a VLAN-based network, switches use VLAN 1 as the default VLAN for in-band management and to communicate with other networking devices using Spanning-Tree Protocol (STP), Cisco Discovery Protocol (CDP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP)--all untagged traffic. As a consequence, VLAN 1 may unwisely span the entire network if not appropriately pruned. If its scope is large enough, the risk of compromise can increase significantly.

STIG	Date
Perimeter L3 Switch Security Technical Implementation Guide - Cisco	2015-04-06

Details

Check Text ( C-4028r3_chk )
Review the device configuration and verify that access ports have not been assigned membership to the VLAN 1. If any access ports are found in VLAN 1, this is a finding.

Fix Text (F-3904r2_fix)
Best practices for VLAN-based networks is to prune unnecessary ports from gaining access to VLAN 1 as well as the management VLAN, and to separate in-band management, device protocol, and data traffic.