74
4.5
VLAN
A Virtual LAN (VLAN) is a “logical” grouping of nodes for the purpose of limiting a
broadcast domain to specific members of a group without physically grouping the members
together. That means, VLAN allows you to isolate network traffic so that only members of
VLAN could receive traffic from the same VLAN members. Basically, creating a VLAN from
a switch is the logical equivalent of physically reconnecting a group of network devices to
another Layer 2 switch, without actually disconnecting these devices from their original
switches.
JetNet 5020G supports 802.1Q VLAN. 802.1Q VLAN is also known as Tag-Based VLAN.
This Tag-Based VLAN allows VLAN to be created across different switches (see Figure 1).
IEEE 802.1Q tag-based VLAN makes use of VLAN control information stored in a VLAN
header attached to IEEE 802.3 packet frames. This tag contains a VLAN Identifier (VID)
that indicates which VLAN a frame belongs to. Since each switch only has to check a
frame’s tag, without the need to dissect the contents of the frame, this also saves a lot of
computing resources within the switch.
Figure 4.5.1 802.1Q VLAN
QinQ
The QinQ is originally
designed to expand the
number of VLANs by
adding a tag to the 802.1Q
packets. The original
VLAN is usually identified
as Customer VLAN
(C-VLAN) and the new
added t–g - as Service
VLAN(S-VLAN). By
adding the additional tag,
QinQ increases the
possible number of VLANs.
After QinQ enabled, the
Managed Switch can
reach up to 256x256 VLANs. With different standard tags, it also improves the network
security.