26. Virtual LANs
ROX™ v2.2 User Guide 267 RuggedBackbone™ RX5000
operate in a VLAN-aware mode while providing functionality required for almost any network application.
However, the IEEE 802.1Q standard defines a set of rules that must be followed by all VLAN-aware
switches:
• Valid VID range is 1 to 4094 (VID=0 and VID=4095 are invalid).
• Each frame ingressing a VLAN-aware switch is associated with a valid VID.
• Each frame egressing a VLAN-aware switch is either untagged or tagged with a valid VID (this means
priority-tagged frames with VID=0 are never sent out by a VLAN-aware switch).
Some applications have requirements conflicting with the IEEE 802.1Q native mode of operation. For
example, some applications explicitly require priority-tagged frames to be received by end devices).
26.1.8. GVRP (GARP VLAN Registration Protocol)
GVRP is a standard protocol built on GARP (the Generic Attribute Registration Protocol) to automatically
distribute VLAN configuration information in a network. Each switch in a network needs only to be
configured with VLANs it requires locally; it dynamically learns the rest of the VLANs configured
elsewhere in the network via GVRP. A GVRP-aware end station, configured for a particular VLAN ID,
can be connected to a trunk on a GVRP-aware switch and automatically become part of the desired
VLAN.
When a switch sends GVRP BPDUs out of all GVRP-enabled ports, GVRP BPDUs advertise all the
VLANs known to that switch (configured manually or learned dynamically through GVRP) to the rest
of the network.
When a GVRP-enabled switch receives a GVRP BPDU advertising a set of VLANs, the receiving port
becomes a member of those advertised VLANs and the switch begins advertising those VLANs via all
the GVRP-enabled ports (other than the port on which the VLANs were learned).
To improve network security using VLANs, GVRP-enabled ports may be configured to prohibit the
learning of any new dynamic VLANs but at the same time be allowed to advertise the VLANs configured
on the switch.
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