Trunking Overview - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Chapter 8 Configuring LAN Ports for Layer 2 Switching

Trunking Overview

For information about VLANs, see
Note
A trunk is a point-to-point link between the switch and another networking device. Trunks carry the
traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.
Two trunking encapsulations are available on all Ethernet ports:
•
•
You can configure a trunk on a single Ethernet port or on an EtherChannel. For more information about
EtherChannel, see
Ethernet trunk ports support several trunking modes (see
whether the trunk uses ISL or 802.1Q encapsulation, and if the encapsulation type is autonegotiated.
Note You can configure LAN ports to negotiate the encapsulation type. You cannot configure WAN interfaces
to negotiate the encapsulation type.
The Dynamic Trunking Protocol (DTP) manages trunk autonegotiation on LAN ports. DTP supports
autonegotiation of both ISL and 802.1Q trunks.
To autonegotiate trunking, the LAN ports must be in the same VTP domain. Use the trunk or
nonegotiate keywords to force LAN ports in different domains to trunk. For more information on VTP
domains, see
Encapsulation Types
Table 8-1
Table 8-1
Encapsulation
switchport trunk encapsulation isl
OL-11439-03
Inter-Switch Link (ISL)—ISL is a Cisco-proprietary trunking encapsulation.
The following switching modules do not support ISL encapsulation:
Note
• WS-X6502-10GE
• WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6548-GE-45AF
• WS-X6148-GE-TX, WS-X6148V-GE-TX, WS-X6148-GE-45AF
802.1Q—802.1Q is an industry-standard trunking encapsulation.
Chapter 10, "Configuring EtherChannels."
Chapter 11, "Configuring VTP."
lists the Ethernet trunk encapsulation types.
Ethernet Trunk Encapsulation Types
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Chapter 12, "Configuring VLANs."
Table 8-2 on page
Function
Specifies ISL encapsulation on the trunk link.
Some modules do not support ISL
Note
encapsulation (see the
Overview" section on page
Understanding How Layer 2 Switching Works
8-4). You can specify
"Trunking
8-3).
8-3