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Example VLAN Trunk Configurations
802.1Q Nonegotiate Trunk Configuration Example
This example configuration shows how to configure an 802.1Q Fast Ethernet trunk between two
Catalyst 4000 family switches with 802.1Q-capable hardware. (Use the show port capabilities
command to see if your hardware is 802.1Q-capable.)
In this example, an 802.1Q trunk is configured between port 1/1 on Switch 1 and port 4/1 on Switch 2.
The initial network configuration is shown in
both ends of the link.
Figure 11-4 802.1Q Trunking: Initial Network Configuration
4000
Switch 1
Step 1
To configure a port as an 802.1Q trunk, enter the set trunk command. You must use the nonegotiate
keyword when configuring a port as an 802.1Q trunk.
Switch 1> (enable) set trunk 1/1 nonegotiate dot1q
Port(s) 1/1 trunk mode set to nonegotiate.
Port(s) 1/1 trunk type set to dot1q.
Switch 1> (enable) 04/15/1998,22:02:17:DISL-5:Port 1/1 has become dot1q trunk
Switch 2> (enable) 04/15/1998,22:01:42:SPANTREE-2: Rcved 1Q-BPDU on non-1Q-trunk port 4/1
vlan 1.
04/15/1998,22:01:42:SPANTREE-2: Block 4/1 on rcving vlan 1 for inc trunk port.
04/15/1998,22:01:42:SPANTREE-2: Block 4/1 on rcving vlan 1 for inc peer vlan 2.
Switch 2> (enable)
Note
Figure 11-5 802.1Q Trunking: Port-Type Inconsistency
Trunk Type: 802.1Q
Trunk Mode: nonegotiate
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
11-18
Port 1/1
Port 4/1
Trunk Type: 802.IQ
Trunk Type: 802.IQ
Trunk Mode: auto
Trunk Mode: auto
After the port on Switch 1 is configured as an 802.1Q trunk, syslog messages are displayed on
the Switch 2 console, and port 4/1 on Switch 2 is blocked. STP blocks the port because there is
a port-type inconsistency on the trunk link: port 1/1 on Switch 1 is configured as an 802.1Q trunk
while port 4/1 on Switch 2 is configured as an ISL trunk (see
be blocked if it were configured as a nontrunk port.
Port 1/1
Trunk Type: 802.IQ
Trunk Mode: auto
Blocking
4000
Switch 1
Port-type
inconsistency
Chapter 11
Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
Figure
11-4. Assume that the native VLAN is VLAN 1 on
4000
Switch 2
Port 4/1
X
4000
Switch 2
Figure
11-5). Port 4/1 would also
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