CCNA VLAN Trunking 7: Trunking Across Three Switches

Bundle lab · $29.99

Build an end-to-end 802.1Q path across three Cisco IOS Layer-2 switches so VLAN 10 transports user traffic from an access port on the left switch to an access port on the right switch through a middle switch. Harden trunks (native VLAN 999, nonegotiate) and verify with show interfaces trunk. Then intentionally break the allow-list to see the outage and restore service.

Learning objectives

• Configure access ports and create VLANs on Layer-2 switches
• Build two 802.1Q trunks that carry VLAN 10 end-to-end across three switches
• Harden trunks by setting a non-default native VLAN and disabling DTP negotiation
• Verify trunk and VLAN transport state with show interfaces trunk
• Diagnose and fix an outage caused by an incomplete trunk allowed-VLAN list

Troubleshooting focus

• Identify where VLAN transport breaks across a multi-switch path using show interfaces trunk and show vlan brief
• Detect and correct a native VLAN mismatch across trunks
• Spot a missing VLAN in a trunk allowed list and restore it
• Verify correct host access VLAN assignment and portfast/bpduguard on access ports