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. 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 frames that
are passed between switches. Access ports also carry traffic
that comes from only the VLAN assigned to the port. A trunk port
is by default a member of all the VLANs that exist on the switch
and carry traffic for all those VLANs between the switches. To
distinguish between the traffic