3Com S7906E Command Reference Manual page 209

Use the undo port trunk pvid command to restore the default.
By default, the default VLAN of a trunk port is VLAN 1.
You can use a nonexistent VLAN as the default VLAN for a trunk port. Removing the default VLAN of a
trunk port with the undo vlan command does not affect the setting of the default VLAN on the port.
In Ethernet interface view, this command only applies to the current port.
In port group view, this command applies to all ports in the port group. For information about port
groups, refer to Ethernet Interface Configuration in the Access Volume.
In Layer-2 aggregate interface view, this command applies to the Layer-2 aggregate interface and
all its member ports. After you perform the configuration, the system starts applying the
configuration to the aggregate interface and its aggregation member ports. If the system fails to do
that on the aggregate interface, it stops applying the configuration to the aggregation member ports.
If it fails to do that on an aggregation member port, it simply skips the port and moves to the next
port. For information about Layer-2 aggregate interfaces, refer to Link Aggregation Configuration in
the Access Volume.
The local and remote trunk ports must use the same default VLAN ID for the traffic of the default
VLAN to be transmitted properly.
After configuring the default VLAN for a trunk port, you must use the port trunk permit vlan
command to configure the trunk port to allow packets from the default VLAN to pass through, so
that the port can forward packets from the default VLAN.
Related commands: port link-type, port trunk permit vlan.
Examples
# Configure VLAN 100 as the default VLAN of the trunk port GigabitEthernet 2/0/1.
<Sysname> system-view
[Sysname] interface GigabitEthernet 2/0/1
[Sysname-GigabitEthernet2/0/1] port link-type trunk
[Sysname-GigabitEthernet2/0/1] port trunk pvid vlan 100
# Configure VLAN 100 as the default VLAN of the trunk Layer-2 aggregate interface
Bridge-aggregation 1, assuming Bridge-aggregation 1 does not have member ports.
<Sysname> system-view
[Sysname] interface bridge-aggregation 1
[Sysname-Bridge-Aggregation1] port trunk pvid vlan 100
# Configure VLAN 100 as the default VLAN of the trunk Layer-2 aggregate interface
Bridge-aggregation 1. Among the member ports of the aggregation group corresponding to
Bridge-aggregation 1, GigabitEthernet 2/0/1 is an access port and GigabitEthernet 2/0/2 is a trunk
port.
<Sysname> system-view
[Sysname] interface bridge-aggregation 1
[Sysname-Bridge-Aggregation1] port trunk pvid vlan 100
Error: Failed to configure on interface GigabitEthernet2/0/1! This port is not a Trunk port!
The output above shows that the configuration on Bridge-aggregation 1 and the member port
GigabitEthernet 2/0/2 succeeded; the configuration on GigabitEthernet 2/0/1 failed because
GigabitEthernet 2/0/1 was not a trunk port.
1-17