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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter11 Configuring Layer 2 Ethernet Interfaces
Default Layer 2 Ethernet Interface Configuration

Layer 2 Interface Modes

Table11-2 lists the Laye r 2 interface modes and describes how they function on Ethernet interfaces.
Note DTP is a point-to-point protocol. However, some internetworking devices might forward DTP frames
improperly. To avoid this problem, ensure that interfaces connected to devices that do not support DTP
are configured with the access keyword if you do not intend to trunk ac ross those links. To enable
trunking to a device that does not support DTP, use the nonegotiate keyword to cause the interface to
become a trunk without generating DTP frames.
Default Layer 2 Ethernet Interface Configuration
Table11-3 shows the Layer 2 Ethern et interface default configuration.
Table11-2 Layer 2 Interface Modes
Mode Purpose
switchport mode access Puts the interface into permanent nontrunking mode and
negotiates to convert the link into a nontrunking link. The
interface becomes a nontrunk interface even if the neighboring
interface does not change.
switchport mode
dynamic desirable
Makes the interface actively attempt to convert the link to a
trunking link. The interface becomes a trunk interface if the
neighboring interface is set to trunk, desirable, or auto mode.
switchport mode dynamic auto Makes the interface convert the link to a trunking link if the
neighboring interface is set to trunk or desirable mode. This is
the default mode for all Ethernet interfaces.
switchport mode trunk Puts the interface into permanent trunking mode and negotiates to
convert the link into a trunking link. The interface becomes a
trunk interface even if the neighboring interface does not change.
switchport nonegotiate Puts the interface into permanent trunking mode but prevents the
interface from generating DTP frames. You must configure the
neighboring interface manually as a trunk interface to establish a
trunking link.
Table11-3 Layer 2 Ethernet Interface Default Configuration
Feature Default Value
Interface mode switchport mode dynamic auto
Trunk encapsulation switchport trunk encapsulation negotiate
Allowed VLAN range VLANs 1–1005
VLAN range eligible for pruning VLANs 2–1001
Default VLAN (for access ports) VLAN 1