Cisco 7609 User Manual

7-3
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
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Chapter 7 Configuring LAN Ports for Layer 2 Switching
Understanding How Layer 2 Switching Works
Trunking Overview
Note For information about VLANs, see Chapter 9, “Configuring VLANs.”
A trunk is a point-to-point link between the router 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:
• Inter-Switch Link (ISL)—ISL is a Cisco-proprietary trunking encapsulation.
Note The following switching modules do not support ISL encapsulation:
• WS-X6501-10GEX4
• WS-X6502-10GE
• WS-X6548-GE-TX
• WS-X6548V-GE-TX
• WS-X6148-GE-TX
• WS-X6148V-GE-TX
• 802.1Q—802.1Q is an industry-standard trunking encapsulation.
You can configure a trunk on a single Ethernet port or on an EtherChannel. For more information about
EtherChannel, see Chapter 13, “Configuring EtherChannels.”
Ethernet trunk ports support several trunking modes (see Table 7-2 on page 7-4). You can specify
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 Chapter 8, “Configuring VTP.”

Cisco 7609 Specifications

General

Brand	Cisco
Model	7609
Category	Network Router
Language	English