PLANET ISW-504PS - Manual (Page 47)

User’s Manual
4.5 VLAN
A Virtual LAN (VLAN) is a logical network grouping that limits the broadcast domain. It allows you to isolate network traffic
so only members of the VLAN receive traffic from the same VLAN members. Basically, creating a VLAN from a switch is
logically equivalent of reconnecting a group of network devices to another Layer 2 switch. However, all the network
devices are still plug into the same switch physically.
The ISW-504PS / ISW-514PS series Ethernet Switch supports 802.1Q (tagged-based) and Port-Base VLAN setting in
web management page. The default configuration of VLAN setting is “Disable”.
Port-based VLAN
Port-based VLAN 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 VLAN, NIC do not need to be able to identify 802.1Q tags in packet headers. NIC 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 is dropped by the Switch or delivered.
IEEE 802.1Q VLAN
IEEE 802.1Q (tagged) VLAN are implemented on the Switch. 802.1Q VLAN require tagging, which enables them to span
the entire network (assuming all switches on the network are IEEE 802.1Q-compliant).
VLAN allow a network to be segmented in order to reduce the size of broadcast domains. All packets entering a VLAN will
only be forwarded to the stations (over IEEE 802.1Q enabled switches) that are members of that VLAN, and this includes
broadcast, multicast and unicast packets from unknown sources.
VLAN can also provide a level of security to your network. IEEE 802.1Q VLAN will only deliver packets between stations
that are members of the VLAN. Any port can be configured as either tagging or untagging. The untagging feature of IEEE
802.1Q VLAN allows VLAN to work with legacy switches that don't recognize VLAN tags in packet headers. The tagging
feature allows VLAN to span multiple 802.1Q-compliant switches through a single physical connection and allows
Spanning Tree to be enabled on all ports and work normally.
Some relevant terms:
Tagging - The act of putting 802.1Q VLAN information into the header of a packet.
Untagging - The act of stripping 802.1Q VLAN information out of the packet header.
802.1Q VLAN Tags
The figure below shows the 802.1Q VLAN tag. There are four additional octets inserted after the source MAC address.
Their presence is indicated by a value of 0x8100 in the Ether Type field. When a packet's Ether Type field is equal to
0x8100, the packet carries the IEEE 802.1Q/802.1p tag. The tag is contained in the following two octets and consists of 3
bits of user priority, 1 bit of Canonical Format Identifier (CFI - used for encapsulating Token Ring packets so they can be
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