Encapsulation Types - Cisco WS-C3750-48PS-S Software Configuration Manual

Configuring VLAN Trunks
You can also specify on DTP interfaces whether the trunk uses ISL or 802.1Q encapsulation or if the
encapsulation type is autonegotiated. The DTP supports autonegotiation of both ISL and 802.1Q trunks.
Note DTP is not supported on private-VLAN ports.
Table 13-4 Layer 2 Interface Modes
Mode
switchport mode access
switchport mode dynamic auto
switchport mode dynamic
desirable
switchport mode trunk
switchport nonegotiate

Encapsulation Types

Table 13-5
Table 13-5 Ethernet Trunk Encapsulation Types
Encapsulation
switchport trunk encapsulation isl
switchport trunk encapsulation dot1q
switchport trunk encapsulation negotiate Specifies that the interface negotiate with the neighboring interface to become
The switch does not support Layer 3 trunks; you cannot configure subinterfaces or use the encapsulation
Note
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 802.1Q trunk.
Catalyst 3750 Switch Software Configuration Guide
13-18
Function
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.
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.
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.
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.
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.
lists the Ethernet trunk encapsulation types and keywords.
Function
Specifies ISL encapsulation on the trunk link.
Specifies 802.1Q encapsulation on the trunk link.
an ISL (preferred) or 802.1Q trunk, depending on the configuration and
capabilities of the neighboring interface. This is the default for the switch.
Chapter 13 Configuring VLANs
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