Default Layer 2 Ethernet Interface Vlan Configuration; Configuring An Ethernet Interface As A Trunk Port - Cisco WS-C3560-48PS-S Software Configuration Manual
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Chapter 12
Configuring VLANs
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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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By default, an interface is in Layer 2 mode. The default mode for Layer 2 interfaces is switchport mode
Note
dynamic auto. 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.
78-16156-01
Make sure the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the
native VLAN on one end of the trunk is different from the native VLAN on the other end,
spanning-tree loops might result.
Disabling spanning tree on the native VLAN of an 802.1Q trunk without disabling spanning tree on
every VLAN in the network can potentially cause spanning-tree loops. We recommend that you
leave spanning tree enabled on the native VLAN of an 802.1Q trunk or disable spanning tree on
every VLAN in the network. Make sure your network is loop-free before disabling spanning tree.
shows the default Layer 2 Ethernet interface VLAN configuration.
Interaction with Other Features, page 12-20
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
Default Setting
switchport mode dynamic auto
switchport trunk encapsulation negotiate
VLANs 1 to 4094
VLANs 2 to 1001
VLAN 1
VLAN 1
Catalyst 3560 Switch Software Configuration Guide
Configuring VLAN Trunks
12-19
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