VLAN Trunking 6: DTP and Trunk Hardening

Bundle lab · $29.99

Hands-on DTP negotiation and trunk hardening across a 3-switch path. You will observe dynamic trunking behavior (auto vs desirable), fix an allow-list drift that blocks user VLAN transport, and then harden the trunks to static with nonegotiate and a non-default native VLAN. End-to-end host reachability in the same VLAN proves success.

Learning objectives

• Differentiate DTP dynamic auto vs dynamic desirable and predict whether a trunk will form.
• Use show interfaces switchport and show interfaces trunk to verify negotiation and trunk state.
• Detect and remediate a trunk allowed-VLAN drift that breaks end-to-end VLAN transport.
• Standardize the native VLAN and verify mismatch detection and resolution.
• Harden trunks to a permanent static 802.1Q configuration so DTP no longer negotiates the trunk, using a non-default native VLAN.
• Harden access ports with portfast, bpduguard, and sticky port-security.

Troubleshooting focus

• Diagnose and resolve the introduced fault: Trunk allow-lists, native VLAN alignment, and host VLAN assignment.
• Verify every link's interface status and IP addressing (`show ip interface brief`) and correct any interface that is down or misaddressed.
• Confirm each device's running configuration matches the lab objective, and bring any interface, route, or service that is not in its expected state back to health.
• Trace end-to-end reachability with ping/traceroute and isolate the first hop where forwarding fails.