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11-19
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
—
Release 8.1
78-15486-01
Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
Example VLAN Trunk Configurations
802.1Q Nonegotiate Trunk Configuration Example
This sample configuration shows how to configure an 802.1Q Fast Ethernet trunk between two
Catalyst 4500 series switches with 802.1Q-capable hardware. (Use the show port capabilities command
to see if your hardware is 802.1Q-capable.) The initial network configuration is shown in
Figure 11-4
.
Assume that the native VLAN is VLAN 1 on both ends of the link.
Figure 11-4 802.1Q Trunking: Initial Network Configuration
To configure an 802.1Q trunk between port 1/1 on Switch 1 and port 4/1 on Switch 2, follow these steps:
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
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
Figure 11-5
). Port 4/1 would also
be blocked if it were configured as a nontrunk port.
Figure 11-5 802.1Q Trunking: Port-Type Inconsistency
4000
4000
Port 1/1 Port 4/1
Trunk Type: 802.IQ Trunk Type: 802.IQ
Trunk Mode: auto Trunk Mode: auto
Switch 1
Switch 2
43993
4000
4000
Port 1/1
Trunk Type: 802.1Q
Trunk Mode: nonegotiate
Switch 1
Port-type
inconsistency
Switch 2
43994
Port 4/1
Trunk Type: 802.IQ
Trunk Mode: auto
X
Blocking