referred to as the native VLAN of the port. Any device attached to an
access link is unaware of a VLAN membership. This device just assumes
it is part of a broadcast domain, with no understanding of the physical
network. Switches remove any VLAN information from the frame before
it is sent to an access link device. Access link devices cannot communicate
with devices outside of their VLAN unless the packet is routed through a
router.
the trunks of the telephone system, which carries multiple telephone con-
versations, trunk links are used to connect switches to other switches, to
routers, or even to servers. Trunked links are supported on FastEthernet
or Gigabit Ethernet only. To identify the VLAN that a frame belongs to,
Cisco switches support two different identification techniques: Inter-
Switch Link (ISL) and 802.1q. Trunk links are used to transport VLANs
between devices and can be configured to transport all VLANs or just a
few VLANs. Trunk links still have a native VLAN, and that VLAN is used
if the trunk link fails.
as they travel the switch-fabric and VLANs. Frame identification (frame tag-
ging) uniquely assigns a user-defined ID to each frame. This is sometimes
referred to as a VLAN ID or color.
switch that the frame reaches must identify the VLAN ID, then make a deter-
mination on what to do with the frame based on the filter table. If the frame
reaches a switch that has another trunked link, the frame will be forwarded
out the trunk link port. Once the frame reaches an exit to an access link, the
switch removes the VLAN identifier. The end device will receive the frames
without having to understand the VLAN identification.
first packet through the router. This means that communication can occur
from port to port on a switch, rather than port to router to port, when tra-
versing VLANs.