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Stackable NWay Ethernet Switch User's Guide
IEEE 802.1Q VLANs
The Switch supports up to 96 IEEE 802.1Q (port-based) VLANs. Port-
based VLANs limit traffic that flows into and out of switch ports.
Thus, all devices connected to a port are members of the VLAN(s) the
port belongs to, whether there is a single computer directly connected
to a switch, or an entire department.
On port-based VLANs, NICs do not need to be able to identify 802.1Q
tags in packet headers. NICs send and receive normal Ethernet
packets. If the packet's destination lies on the same segment,
communications take place using normal Ethernet protocols. Even
though this is always the case, when the destination for a packet lies
on another switch port, VLAN considerations come into play to decide
if the packet gets dropped by the switch or delivered.
There are two key components to understanding IEEE 802.1Q
VLANs; Port VLAN ID numbers (PVID) and VLAN ID numbers
(VID). Both variables are assigned to a switch port, but there a re
important differences between them. A user can only assign one
PVID to each switch port. The PVID defines which VLAN a switch
will forward packets from the connected segment on, when packets
need to be forwarded to another switch port or somewhere else on the
network. On the other hand, a user can define a port as a member of
multiple VLANs (VIDs), allowing the segment connected to it to
receive packets from many VLANs on the network. These two
variables control a port's ability to transmit and receive VLAN
traffic,
and
the
difference
between
them
provides
network
segmentation, while still allowing resources to be shared across more
than one VLAN.
VLAN Segmentation
Take for example a packet that is transmitted by a machine on Port
1 that is a member of VLAN 2 and has the Port VLAN ID number 2
(PVID=2). If the destination lies on another port (found through a
normal forwarding table lookup), the switch then looks to see if the
Switch Management Concepts
43
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