EFM User Manual - CTC Union Technologies Co.,Ltd.

Before enabling VLANs for the EFM modem, you must first assign each port to the VLAN
group(s) in which it will participate. By default all ports are assigned to VLAN1 as untagged
ports. Add a port as a tagged port if you want it to carry traffic for one or more VLANs, and any
intermediate network devices or the host at the other end of the connection supports VLANs.
Then assign ports on the other VLAN-aware network devices along the path that will carry this
traffic to the same VLAN(s), either manually or dynamically using GVRP. However, if you want
a port on this EFM modem to participate in one or more VLANs, but none of the intermediate
network devices nor the host at the other end of the connection supports VLANs, then you
should add this port to the VLAN as an untagged port.
Note: VLAN-tagged frames can pass through VLAN-aware or VLAN-unaware network
Inter-connection devices, but the VLAN tags should be stripped off before passing it on to any
end-node host that does not support VLAN tagging.
VLAN Classification – When the EFM modem receives a frame, it classifies the frame in one of
two ways. If the frame is untagged, the EFM modem assigns the frame to an associated VLAN
(based on the default VLAN ID of the receiving port). But if the frame is tagged, the EFM
modem uses the tagged VLAN ID to identify the port broadcast domain of the frame.
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.
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 EFM modem. 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.
PVID - VLAN ID assigned to untagged frames received on the interface. (Default: 1)
If an interface is not a member of VLAN 1 and you assign its PVID to this VLAN, the interface
will automatically be added to VLAN 1 as an untagged member. For all other VLANs, an
interface must first be configured as an untagged member before you can assign its PVID to
that group.
Link Type - Sets the port to accept the frame types: "Access" means the port can only receive
or send untagged frame types. "Trunk" means that the port can only receive or send tagged
frame types.
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