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MAGNUM 6K SWITCHES, MNS-6K USER GUIDE
In the tag VLAN, an identifier called the VLAN identifier (VID) is either inserted or
manipulated. This manipulated VLAN tag allows VLAN information to be propagated across
devices or switches, allowing VLAN information to span multiple switches.
As described earlier, VLAN is an administratively configured LAN or broadcast domain. Instead
of going to the wiring closet to move a cable to a different LAN segment, the same task can be
accomplished remotely by configuring a port on an 802.1Q-compliant switch to belong to a
different VLAN. The ability to move end stations to different broadcast domains by setting
membership profiles for each port on centrally managed switches is one of the main advantages
of 802.1Q VLANs.
802.1Q VLANs aren't limited to one switch. VLANs can span many switches. Sharing VLANs
between switches is achieved by inserting a tag with a VLAN identifier (VID) into each frame. A
VID must be assigned for each VLAN. By assigning the same VID to VLANs on many switches,
one or more VLAN (broadcast domain) can be extended across a large network.
802.1Q-compliant switch ports, such as those on the Magnum 6K family of switches, can be
configured to transmit tagged or untagged frames. A tag field containing VLAN information can
be inserted into an Ethernet frame. If a port has an 802.1Q-compliant device attached (such as
another switch), these tagged frames can carry VLAN membership information between switches,
thus letting a VLAN span multiple switches. Normally connections between switches can carry
multiple VLAN information and this is call port trunking or 802.1Q trunks.
There is one important caveat: administrators must ensure ports with non-802.1Q-compliant
devices attached are configured to transmit untagged frames. Many network interface cards such
as those for PCs printers and other “dumb” switches are not 802.1Q-compliant. If they receive a
tagged frame, they will not understand the VLAN tag and will drop the frame. In situations like
these, its best to use port based VLANs for connecting to these devices.
Sometimes a port may want to listen to broadcasts across different VLANs or propagate the
VLAN information on to other ports. This port must thus belong to multiple VLANs so that the
broadcast information reaches the port accurately. If the port also wants to send broadcast traffic,
the proper egress (sending out of information) and ingress (receiving information) has to be
configured on the Magnum 6K family of switches. In Tag based VLAN this is similar but only if
the port is tagged for each VLAN.
Private VLANs
Private VLANs are VLANs which are private to a given switch in a network. For Magnum 6K
family of switches, the Private VLANs are usually restricted to a single switch. Private
VLANs are implemented on Magnum 6K family of switches using Port based VLAN. See the
section on Port VLAN for additional information.
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