Allied Telesis AT-S80, User Manual

Page: 102 / 346

Chapter 10: Virtual LANs
102 Section I: Using the Menus Interface
The IEEE 802.1Q standard describes how tagging information within a
packet is used to forward or discard traffic throughout the switch. If the
incoming packet has a VLAN tag that matches one of the Group IDs of
which the port is a member, the packet is accepted and forwarded to the
appropriate port(s) within that VLAN. If the incoming packet’s VLAN tag
does not match one of the Group IDs assigned to the port, the packet is
discarded.
Port VLAN
Identifier
When an untagged packet is received on a port in a tagged VLAN, it is
assigned to one of the VLANs of which that port is a member. The
deciding factor in this process is the Port VLAN Identifier (PVID). Both
tagged and untagged ports in a tagged VLAN must have a PVID assigned
to them. The default value of the PVID for each port is 1. The switch
associates a received untagged packet to the Group ID that matches the
PVID assigned to the port. As a result, the packet is only forwarded to
those ports that are members of that VLAN.
General Rules for
Creating a
Tagged VLAN
Below is a summary of the rules to observe when you create a tagged
VLAN.
ˆ
Each tagged VLAN must be assigned a unique VID. If a particular
VLAN spans multiple switches, each part of the VLAN on the different
switches must be assigned the same VID.
ˆ
A tagged port can be a member of multiple VLANs.
ˆ
The AT-FS750/16 and AT-FS750/24 switches can support up to 48
tagged VLANS.