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Cisco® Field Manual: Catalyst® Switch Configuration by Steve McQuerry, Dave Hucaby

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6-3. Trunking

  • VLANs are local to each switch's database, and VLAN information is not passed between switches.

  • Trunk links provide VLAN identification for frames traveling between switches.

  • Cisco switches have two Ethernet trunking mechanisms: ISL and IEEE 802.1Q.

  • Certain types of switches can negotiate trunk links.

  • Trunks carry traffic from all VLANs to and from the switch by default but can be configured to carry only specified VLAN traffic.

  • Trunk links must be configured to allow trunking on each end of the link.

Enabling Trunking

Trunk links are required to pass VLAN information between switches. A port on a Cisco switch is either an access port or a trunk port. Access ports belong to a single VLAN and do not provide any identifying marks on the ...

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