An example VLAN configured through the use of global config mode
on a single switch. To support multiple VLANs that span multiple
switches one uses trunks. A trunk carries the traffic of
multiple VLANs over links (multiplexing) and enable the
extension of a single layer-2 VLAN between switches. A trunk can
exist between two switches, a switch and a router, a switch and
a trunk-capable NIC (server). If a physical link carries
multiple VLANs (trunk) then each frame going onto the link must
be market with a VLAN ID (VID) which is added when entering into
the link and removed when forwarded to a access port. This is
accomplished through the use of trunking protocols. The two
trunking protocols are ISL or Cisco ISL (proprietary) and 802.1Q
which is IEEE standard trunking protocol. Depending on the
trunking protocol as shown above the data sent across a trunk
link is either proprietary to cisco, cross platform (dont you
know thats going to be an exam question, encapsulated or tagged,
and protocol independant or pro