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■ Port Overlapping
Port overlapping can be used to allow access to commonly shared network resources among different VLAN groups, such as
file servers or printers. Note that if you implement VLANs which do not overlap, but still need to communicate, you can connect
them by enabled routing on this switch.
■ 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.
4.6.3 VLAN Port Configuration
This Page is used for configuring the Managed Switch port VLAN. The VLAN per Port Configuration Page contains fields for
managing ports that are part of a VLAN. The port default VLAN ID (PVID) is configured on the VLAN Port Configuration Page.
All untagged packets arriving to the device are tagged by the ports PVID.
Understand nomenclature of the Switch
■ IEEE 802.1Q Tagged and Untagged
Every port on an 802.1Q compliant switch can be configured as tagged or untagged.
Tagged:
Ports with tagging enabled will put the VID number, priority and other VLAN information into the
header of all packets that flow into those ports. If a packet has previously been tagged, the port
will not alter the packet, thus keeping the VLAN information intact. The VLAN information in the
tag can then be used by other 802.1Q compliant devices on the network to make
packet-forwarding decisions.
Untagged:
Ports with untagging enabled will strip the 802.1Q tag from all packets that flow into those
ports. If the packet doesn't have an 802.1Q VLAN tag, the port will not alter the packet. Thus,
all packets received by and forwarded by an untagging port will have no 802.1Q VLAN
information. (Remember that the PVID is only used internally within the Switch). Untagging is
used to send packets from an 802.1Q-compliant network device to a non-compliant network
device.
Frame Income
Frame Leave
Leave port is tagged
Leave port is untagged
Income Frame is tagged
Frame remains tagged
Tag is removed
Table 4-6-1: Ingress / Egress Port with VLAN VID Tag / Untag Table
User's Manual of MGSW-MGSD Series
Income Frame is untagged
Tag is inserted
Frame remain untagged
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