Cisco WS-C2948G-GE-TX - 802.1 Q Nonegotiate Trunk Configuration Example

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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
Example VLAN Trunk Configurations
802.1Q Nonegotiate Trunk Configuration Example
This 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 you configure the port on Switch 1 as an 802.1Q trunk, syslog messages display 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 as an 802.1Q trunk while
port 4/1 on Switch 2 is 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
Step 2
Display the problem on Switch 2 by entering the show spantree and show spantree statistics
commands. The configuration mismatch exists until the port on Switch 2 is properly configured.
Port 1/1 Port 4/1
Trunk Type: 802.IQ Trunk Type: 802.IQ
Trunk Mode: auto Trunk Mode: auto
Switch 1 Switch 2
99515
Port 1/1
Trunk Type: 802.1Q
Trunk Mode: nonegotiate
Switch 1 Port-type
inconsistency
Switch 2
99516
Port 4/1
Trunk Type: 802.IQ
Trunk Mode: auto
X
Blocking