Cisco Catalyst 2960 Series, Configuration Manual

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Layer 2 Interface Modes
Table 195: Layer 2 Interface Modes
Function Mode
Puts the interface (access port) into permanent
nontrunking mode and negotiates to convert the link
into a nontrunk link. The interface becomes a
nontrunk interface regardless of whether or not the
neighboring interface is a trunk interface.
switchport mode access
Makes the interface able to convert the link to a trunk
link. The interface becomes a trunk interface if the
neighboring interface is set to
trunk or desirable
mode. The default switchport mode for all Ethernet
interfaces is
dynamic auto .
switchport mode dynamic auto
Makes the interface actively attempt to convert the
link to a trunk link. The interface becomes a trunk
interface if the neighboring interface is set to
trunk
,
desirable
, or
auto
mode.
switchport mode dynamic desirable
Puts the interface into permanent trunking mode and
negotiates to convert the neighboring link into a trunk
link. The interface becomes a trunk interface even if
the neighboring interface is not a trunk interface. switchport mode trunk
Prevents the interface from generating DTP frames.
You can use this command only when the interface
switchport mode is
access
or
trunk
. You must
manually configure the neighboring interface as a
trunk interface to establish a trunk link.
switchport nonegotiate
Related Topics
Configuring a Trunk Port , on page 2134
Trunking Modes, on page 2130
Allowed VLANs on a Trunk
By default, a trunk port sends traffic to and receives traffic from all VLANs. All VLAN IDs, 1 to 4094, are
allowed on each trunk. However, you can remove VLANs from the allowed list, preventing traffic from those
VLANs from passing over the trunk.
To reduce the risk of spanning-tree loops or storms, you can disable VLAN 1 on any individual VLAN trunk
port by removing VLAN 1 from the allowed list. When you remove VLAN 1 from a trunk port, the interface
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About VLAN Trunks