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CCNP Practical Studies: Troubleshooting by Donna L. Harrington

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Trunking

Routing provides inter-VLAN connectivity, whereas trunking provides intra-VLAN connectivity. Trunks, whether between switches, from a router to a switch, or from a switch to a file server, minimize the number of interfaces and cables to transport multi-VLAN traffic.

There are various methods of multiplexing VLANs in trunking:

  • Cisco

    - Ethernet—ISL or 802.1Q

    - FDDI—802.10

    - ATM—LAN Emulation (LANE) or multiprotocol over ATM (MPOA)

  • Mixed-vendor environment

    - 802.1Q

    - LANE or MPOA

Cisco uses its own proprietary ISL and the standards-based IEEE 802.1Q for trunking. (See Figure 7-4.) However, Cisco has started to favor 802.1Q over ISL. Some newer switches such as the 2950 support only 802.1Q.

Figure 7-4. Trunking

Go ahead and configure ISL trunking ...

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