User’s Manual: SW-10200
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device to another with VLAN information intact. This allows 802.1Q VLANs to span network devices or even the
entire network provided that all network devices are 802.1Q compliant.
All physical ports on a switch have a PVID. 802.1Q ports are also assigned a PVID for use within the switch. If
no VLANs are defined on the switch, all ports are then assigned to a default VLAN with a PVID equal to 1. Any
untagged packet is assigned the PVID of the port on which they were received. Forwarding decisions are based
upon this PVID in so far as VLAN are concerned. Tagged packets are forwarded according to the VID contained
within the tag. Tagged packets are also assigned a PVID, but the VID is used to make packet forwarding decisions,
rather than the PVID.
Tag-aware switches must keep a table to relate PVID within the switch to a network VID. The switch will
compare the VID of a packet to be transmitted to the VID of the port that is to transmit the packet. If the two VIDs
are different the switch, the packet is dropped. Because of the existence of the PVID for untagged packets and the
VID for tagged packets, tag-aware and tag-unaware network devices are allowed to coexist on the same network.
A switch port can have only one PVID, but can have as many VIDs as the switch has memory in its VLAN
table to store them.
Because some devices on a network may be tag-unaware, a decision must be made at each port on a tag-
aware device before packets are transmitted. If the transmitting port is connected to a tag-unaware device, the
packet should be untagged. If the transmitting port is connected to a tag-aware device, the packet should be
tagged.
Untagged VLANs
Untagged (or static) VLANs are typically used to reduce broadcast traffic and to increase security. A group of
network users assigned to a VLAN form a broadcast domain that is separate from other VLANs configured on the
switch. Packets are forwarded only between ports that are designated for the same VLAN. Untagged VLANs can be
used to manually isolate user groups or subnets.
5.2. VLAN Configuration
To access VLAN options, click on the link
VLAN Configuration
in the navigation pane of the web interface.
5.2.1. VLAN Mode
You may select the VLAN Mode of the switch. Port-based VLAN groups traffic onto a single switch. There is
no handover of network traffic within VLAN groups to other switches. For the handover to other switches use Tag
Based VLAN. In VLAN Mode you can switch from Tag to Port Based VLAN. Port Based VLAN is the default mode.
Click
Change VLAN mode
to change the VLAN mode to Tag Based VLAN. This message may appear.
Figure 19 - Changing VLAN modes causes default VLAN settings to be loaded
Click
Continue
to confirm and to edit settings. The next screen will appear.