Because the frame is encapsulated with information, only ISL-aware devices
can read the frame. Also, the size of the frame can be up to 1,522 bytes long.
tagged with multiple VLANs so the frames can traverse multiple VLANs
without going though a router, which reduces latency. This technology can
also be used with probes and certain network analyzers. In addition, it makes
it easy for users to attach to servers quickly and efficiently without going
through a router every time they need to communicate with a resource.
Administrators can use the ISL technology to simultaneously include file
servers in multiple VLANs, for example.
The ISL encapsulation is removed from the frame if the frame is forwarded
out an access link.
(IEEE 802.1q)
with a new ISL encapsulation, 802.1q uses an internal tagging process by
modifying the existing internal Ethernet frame. To access both links and
trunk links, the frame looks as if it is just a standard Ethernet frame because
it is not encapsulated with VLAN information. The VLAN information is
added to a field within the frame itself.
mat, which allows for the VLAN implementations of multiple vendors. The
standard tag allows for an open architecture and standard services for
VLANs and a standard for protocols in the provision of these services.
Because adding VLAN information to a frame affects the frame length, two
committees were created to deal with this issue: 802.3ac and 802.1q.
address field and the Type or Length field. The CRC of the frame must be
recomputed whenever the VLAN information is inserted or removed from
the frame. The Ethernet frame size can now be up to 1,522 bytes if a tag is
inserted.