Configuring An Ethernet Interface As A Trunk Port; Interaction With Other Features - Cisco Catalyst 2975 Software Configuration Manual

Chapter 13 Configuring VLANs

Configuring an Ethernet Interface as a Trunk Port

Because trunk ports send and receive VTP advertisements, to use VTP you must ensure that at least one
trunk port is configured on the switch and that this trunk port is connected to the trunk port of a second
switch. Otherwise, the switch cannot receive any VTP advertisements.
These sections contain this configuration information:
•
•
•
•

Interaction with Other Features

Trunking interacts with other features in these ways:
•
•
•
•
•
OL-19720-02
Interaction with Other Features, page 13-15
Defining the Allowed VLANs on a Trunk, page 13-17
Changing the Pruning-Eligible List, page 13-18
Configuring the Native VLAN for Untagged Traffic, page 13-19
A trunk port cannot be a secure port.
Trunk ports can be grouped into EtherChannel port groups, but all trunks in the group must have the
same configuration. When a group is first created, all ports follow the parameters set for the first
port to be added to the group. If you change the configuration of one of these parameters, the switch
propagates the setting you entered to all ports in the group:
allowed-VLAN list.
–
STP port priority for each VLAN.
–
STP Port Fast setting.
–
– trunk status: if one port in a port group ceases to be a trunk, all ports cease to be trunks.
We recommend that you configure no more than 24 trunk ports in PVST mode and no more than 40
trunk ports in MST mode.
If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802.1x is not
enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the port mode is
not changed.
A port in dynamic mode can negotiate with its neighbor to become a trunk port. If you try to enable
IEEE 802.1x on a dynamic port, an error message appears, and IEEE 802.1x is not enabled. If you
try to change the mode of an IEEE 802.1x-enabled port to dynamic, the port mode is not changed.
Catalyst 2975 Switch Software Configuration Guide
Configuring VLAN Trunks
13-15