User Documentation

User Manual Managed Switches
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Communication between VLANs
If devices connected to a VLAN need to communicate to devices on a different VLAN, a router or
Layer 3 switching device with connections to both VLANs needs to be installed. Communication
between VLANs can only take place if they are all connected to a routing or Layer 3 switching device.
VLANs: Tagged and Untagged Membership
The Weidmüller switch supports 802.1Q VLAN tagging, a system that allows traffic for multiple
VLANs to be carried on a single physical (backbone, trunk) link. When setting up VLANs you need to
understand when to use untagged and tagged membership of VLANs. Simply put, if a port is on a
single VLAN it can be an untagged member, but if the port needs to be a member of multiple VLANs,
tagged membership must be defined.
A typical host (e.g., clients) will be untagged members of one VLAN, defined as "Access Port" in the
Weidmüller switch, while inter-switch connections will be tagged members of all VLANs, defined as
"Trunk Port" in the Weidmüller switch.
The IEEE Std 802.1Q-1998 defines how VLANs operate within an open packet-switched network. An
802.1Q compliant packet carries additional information that allows a switch to determine which VLAN
the port belongs. If a frame is carrying the additional information, it is known as a tagged frame.
To carry multiple VLANs across a single physical (backbone, trunk) link, each packet must be tagged
with a VLAN identifier so that the switches can identify which packets belong to which VLAN. To
communicate between VLANs, a router must be used.
The Weidmüller switch supports three types of VLAN port settings:
 Access Port: The port connects to a single device that is not tagged. The user must define the
default port PVID that assigns which VLAN the device belongs to. Once the ingress packet of this
Access Port egresses to another Trunk Port (the port needs all packets to carry tag information),
the switch will insert this PVID into this packet so the next 802.1Q VLAN switch can recognize it.
 Trunk Port: The port connects to a LAN that consists of untagged devices, tagged devices
and/or switches and hubs. In general, the traffic of the Trunk Port must have a Tag. Users can
also assign a PVID to a Trunk Port. The untagged packet on the Trunk Port will be assigned the
port default PVID as its VID.
 Hybrid Port: The port is similar to a Trunk port, except users can explicitly assign tags to be
removed from egress packets.
The following section illustrates how to use these ports to set up different applications.
Sample Applications of VLANs Using Weidmüller Switches