Trunking

Trunking
Trunk links are point-to-point, 100Mbps, or 1000Mbps links between two switches, between
a switch and a router, or between a switch and a server. Trunk links carry the traffic of multiple
VLANs, from 1 to 1005 at a time. You cannot run trunk links on 10Mbps links.
Cisco switches use the Dynamic Trunking Protocol (DTP) to manage trunk negation in the
Catalyst switch engine software release 4.2 or later, using either ISL or 802.1Q. DTP is a pointto-
point protocol and was created to send trunk information across 802.1Q trunks. Dynamic
ISL (DISL) was used to support trunk negation on ISL links only before DTP was released in
software release 4.1; and before DISL, auto-negotiation of trunk links was not allowed.
A trunk is a port that supports multiple VLANs, but before it became a trunk, it was the
member of a single VLAN. The VLAN it is a member of when it becomes a trunk is called a
native VLAN. If the port were to lose the trunking ability, it would revert to membership in
its native VLAN.