Verify that management VLAN has been reassigned. Verify that operational VLANs do not have access to the management VLAN. Verify that the ports in the management VLAN are not configured as trunks.

A trunk is a point-to-point link between two network devices that carries traffic for more than one VLAN. A trunk allows you to extend the VLANs across an entire network. A trunk does not belong to a specific VLAN, rather it is a conduit for VLANs between switches and routers.

DTP is implemented by default on Cisco switches. DTP automatically negotiates how the port will operate, trunk or access mode. By default, a Cisco Ethernet port's default DTP mode is "dynamic desirable”, which enables a port to go to trunk mode automatically. Review the switch configuration to verify that DTP is disabled.

 VTP is a Cisco-proprietary messaging protocol used to distribute VLAN configuration information over trunks.  A switch may be in one of three VTP modes: server, transparent and client.  In server mode administrators can create, modify and delete VLANs for the entire VTP management domain.  By default, VTP – no authentication and the switch is in VTP Server mode.

If VTP is necessary, verify the following: VTP management domain is established. A strong password is assigned to the VTP management domain. Non-management switches are configured in client mode.

By auditing device for these basic hardening steps, overall security of the network can be improved. However, in all cases, a comprehensive review should be performed. Reference the works cited page for links to documented security configuration benchmarks and checklists.

Mark Krawczyk

Router Security Guidance Activity of the System and Network Attack Center (SNAC), Cisco IOS Switch Security Configuration Guide, Center for Internet Security, US-Cert, Information Assurance Support Environment, SANS Institute InfoSec Reading Room - Cisco Router Hardening Step-by-Step Cisco Checklist - Configuring a Cisco Router with TACACS+ Authentication. access-control-system-tacacs-/13865-tacplus.html access-control-system-tacacs-/13865-tacplus.html Cisco Guide to Harden Cisco IOS Devices, Document ID: Various Articles related to Cisco device security, NIST – National Vulnerability Database ISACA –