Cisco Systems 3750E manual Encapsulation Types, Mode Function, Encapsulation Function, 13-18

Chapter 13 Configuring VLANs

Configuring VLAN Trunks

Table 13-4	Layer 2 Interface Modes
Mode		Function
switchport mode access		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 dynamic auto		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		Makes the interface actively attempt to convert the link to a trunk link. The interface
desirable		becomes a trunk interface if the neighboring interface is set to trunk, desirable, or auto
		mode.
switchport mode trunk		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 nonegotiate		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 mode dot1q-tunnel		Configures the interface as a tunnel (nontrunking) port to be connected in an asymmetric
		link with an IEEE 802.1Q trunk port. The IEEE 802.1Q tunneling is used to maintain
		customer VLAN integrity across a service provider network. See Chapter 17,
		“Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling,” for more information on
		tunnel ports.

Encapsulation Types

Table 13-5lists the Ethernet trunk encapsulation types and keywords.

Table 13-5 Ethernet Trunk Encapsulation Types

Encapsulation	Function
switchport trunk encapsulation isl	Specifies ISL encapsulation on the trunk link.
switchport trunk encapsulation dot1q	Specifies IEEE 802.1Q encapsulation on the trunk link.
switchport trunk encapsulation negotiate	Specifies that the interface negotiate with the neighboring interface to become
	an ISL (preferred) or IEEE 802.1Q trunk, depending on the configuration and
	capabilities of the neighboring interface. This is the default for the switch.

Note The switch does not support Layer 3 trunks; you cannot configure subinterfaces or use the encapsulation keyword on Layer 3 interfaces. The switch does support Layer 2 trunks and Layer 3 VLAN interfaces, which provide equivalent capabilities.

The trunking mode, the trunk encapsulation type, and the hardware capabilities of the two connected interfaces decide whether a link becomes an ISL or IEEE 802.1Q trunk.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
13-18	OL-9775-02