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C-12 APPENDIX C: ATM AND VLAN MANAGEMENT BASICS
Trunk (VLT). A VLT port in one switch unit must be connected only to a
VLT port in the second switch unit so that the traffic can be switched to
the correct VLAN.
Tagging To distinguish between data frames belonging to different
VLANS which are sent over a common VLT between two switch units,
frame tagging is employed. Each frame which is sent along the VLT is
tagged with a VLAN identifier.
The tag is added to the frame (encapsulated) by the transmitting switch
port and is removed by the receiving switch port, restoring the original
frame. Alteration of the original frame only occurs in transmissions
between switch devices and is not propagated to the rest of the network.
Protocol-based VLANs
Protocol-based
vLANS
In the LANplex 2500/6000, VLAN membership is based on a set of
policies, or criteria, for grouping users.
Protocol-based VLANs group one or more switch ports together for a
specified network layer 3 protocol, such as IP or AppleTalk. These VLANs
make flooding decisions based on the network layer protocol of the
frame. In addition, for IP VLANs, you can also make flooding decisions
based on layer 3 subnet address information.
Protocol-sensitive VLANs allow the restriction of flood traffic for both
routable and non-routable protocols. They have a relatively simple
configuration comprising one or more protocols and groups of switch
ports. These protocol-sensitive VLANs operate independently of each
other and are simple to configure.
One port in multiple
VLANs
Additionally, the same switch port can belong to multiple VLANs. For
example, you could have port 1 on a LANplex assigned to several IP
subnet VLANs, plus one IPX VLAN, one AppleTalk VLAN, and one NetBIOS
VLAN. In a multiprotocol environment, protocol-sensitive VLANs can be
very effective for controlling broadcast and multicast flooding.
Protocol Suite The protocol suite describes which protocol entities can comprise a
protocol-based VLAN. For example, LANplex VLANs support the IP
protocol suite, which is made up of the IP, ARP, and RARP protocols.