Cisco WS-C4003 Software Guide - Page 197
Disabling VLAN 1 on a Trunk Link
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Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports Disabling VLAN 1 on a Trunk Link Step 6 Port Vlans allowed on trunk 4/1 1-1005 Port Vlans allowed and active in management domain 4/1 1-3,1003,1005 Port Vlans in spanning tree forwarding state and not pruned 4/1 1005 Switch 2> (enable) show spantree 1 VLAN 1 Spanning tree enabled Spanning tree type ieee Designated Root 00-60-09-79-c3-00 Designated Root Priority 32768 Designated Root Cost 0 Designated Root Port 1/0 Root Max Age 20 sec Hello Time 2 sec Forward Delay 15 sec Bridge ID MAC ADDR Bridge ID Priority Bridge Max Age 20 sec 00-60-09-79-c3-00 32768 Hello Time 2 sec Forward Delay 15 sec Port Vlan Port-State 1/1 1 not-connected 1/2 1 not-connected 4/1 1 forwarding 4/2 1 not-connected Switch 2> (enable) Cost ----- 4 4 100 100 Priority -------- 32 32 32 32 Fast-Start ---------- disabled disabled disabled disabled Group-method The output shows that port 4/1 is an 802.1Q trunk port, that its status is "trunking," and that the port-state is "forwarding." Verify connectivity across the trunk using the ping command: Switch 1> (enable) ping switch_2 switch_2 is alive Switch 1> (enable) Disabling VLAN 1 on a Trunk Link On the Catalyst enterprise LAN switches, VLAN 1 is enabled by default to allow control protocols to transmit and receive packets across the network topology. However, when VLAN 1 is enabled on trunk links in a large complex network topology, the impact of broadcast storms increases. Because spanning tree applies to the entire network topology, the possibility of spanning tree loops also increases when VLAN 1 is enabled on all trunk links. To prevent this situation, you can disable VLAN 1 on trunk interfaces. When you disable VLAN 1 on a trunk interface, no user traffic is transmitted or received across that trunk interface, but the supervisor engine will continue to transmit and receive packets from control protocols such as Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Port Aggregation Protocol (PAgP), Dynamic Trunking Protocol (DTP), and so forth. 78-12647-02 Software Configuration Guide-Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4 11-21