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Chapter 11
Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
Port
--------
4/1
Port
--------
4/1
Port
--------
4/1
Switch 2> (enable) show spantree 1
VLAN 1
Spanning tree enabled
Spanning tree type
Designated Root
Designated Root Priority
Designated Root Cost
Designated Root Port
Root Max Age
Bridge ID MAC ADDR
Bridge ID Priority
Bridge Max Age 20 sec
Port
--------- ----
1/1
1/2
4/1
4/2
<...output truncated...>
Switch 2> (enable)
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."
Step 6
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
Vlans allowed on trunk
---------------------------------------------------------------------
1-1005
Vlans allowed and active in management domain
---------------------------------------------------------------------
1-3,1003,1005
Vlans in spanning tree forwarding state and not pruned
---------------------------------------------------------------------
1005
ieee
00-60-09-79-c3-00
32768
0
1/0
20 sec
Hello Time 2
00-60-09-79-c3-00
32768
Hello Time 2
Vlan
Port-State
-------------
1
not-connected
1
not-connected
1
forwarding
1
not-connected
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
sec
Forward Delay 15 sec
sec
Forward Delay 15 sec
Cost
Priority
Fast-Start
-----
--------
----------
4
32
disabled
4
32
disabled
100
32
disabled
100
32
disabled
Disabling VLAN 1 on a Trunk Link
Group-method
------------
11-21
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Troubleshooting
