Trunking Overview - Cisco 7609 Configuration Manual
Cisco ios software configuration guide—12.1e
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Chapter 7
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 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:
•
•
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
78-14064-04
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.
Chapter 13, "Configuring EtherChannels."
Chapter 8, "Configuring VTP."
Chapter 9, "Configuring VLANs."
Table 7-2 on page
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
Understanding How Layer 2 Switching Works
7-4). You can specify
7-3
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