Default Layer 2 Ethernet Interface Vlan Configuration - Cisco Catalyst 3550 series Software Configuration Manual

Chapter 12 Configuring VLANs

Default Layer 2 Ethernet Interface VLAN Configuration

Table 12-6
Table 12-6 Default Layer 2 Ethernet Interface VLAN Configuration
Feature
Interface mode
Trunk encapsulation
Allowed VLAN range
VLAN range eligible for pruning
Default VLAN (for access ports)
Native VLAN (for 802.1Q trunks)
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.
This section includes these procedures for configuring an Ethernet interface as a trunk port on the switch:
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Note By default, an interface is in Layer 2 mode. The default mode for Layer 2 interfaces is switchport mode
dynamic desirable. If the neighboring interface supports trunking and is configured to allow trunking,
the link is a Layer 2 trunk or, if the interface is in Layer 3 mode, it becomes a Layer 2 trunk when you
enter the switchport interface configuration command. By default, trunks negotiate encapsulation. If the
neighboring interface supports ISL and 802.1Q encapsulation and both interfaces are set to negotiate the
encapsulation type, the trunk uses ISL encapsulation.
Interaction with Other Features
Trunking interacts with other features in these ways:
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78-11194-09
shows the default Layer 2 Ethernet interface VLAN configuration.
Interaction with Other Features, page 12-19
Defining the Allowed VLANs on a Trunk, page 12-21
Changing the Pruning-Eligible List, page 12-22
Configuring the Native VLAN for Untagged Traffic, page 12-23
A trunk port cannot be a tunnel 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 that you entered to all ports in the group:
– allowed-VLAN list
– STP port priority for each VLAN
– STP Port Fast setting
Default Setting
switchport mode dynamic desirable
switchport trunk encapsulation negotiate
VLANs 1 to 4094
VLANs 2 to 1001
VLAN 1
VLAN 1
Catalyst 3550 Multilayer Switch Software Configuration Guide
Configuring VLAN Trunks
12-19