Riverstone Networks WICT1-12 - Manual (Page 79)

Riverstone Networks RS Switch Router User Guide Release 8.0 5-15
Bridging Configuration Guide GARP/GVRP
5.11 GARP/GVRP
The Generic Attribute Registration Protocol (GARP) is a generic attribute dissemination mechanism. In the case of the
GARP VLAN Registration Protocol (GVRP), the attribute is the VLAN ID (VID).
GVRP uses GARP Protocol Data Units (PDUs) to register and de-register VLAN IDs on ports. When you enable
GVRP on the RS and one of its ports receives a GVRP request for an existing VLAN to which it does not belong,
GVRP registers the VLAN ID on the port, effectively adding the port to the VLAN. For example, VLAN RED is
configured on ports et.1.1 and et.1.2 of the RS. Port et.1.3 receives a GVRP request for VLAN RED, of which it is not
a member. If GVRP is enabled on port et.1.3, it will autmoatically become a member of VLAN RED and pass traffic
for this VLAN. But if GVRP is not enabled on port et.1.3, VLAN registration will not occur, and traffic for VLAN
RED will never reach port et.1.3.
GVRP also provides a mechanism for dynamically creating and removing VLANs. When you turn on dynamic VLAN
creation and the RS receives a request for a VLAN that does not exist on the RS, GVRP dynamically creates that
VLAN and adds the port that received the request.
GVRP propagates this VLAN information throughout the active topology, enabling all GVRP-aware devices to
dynamically establish and update their knowledge of VLANS and their members, including the ports through which
those members can be reached. (For details on GARP refer to IEEE 802.1d. For details on GVRP, refer to IEEE
802.1q.)
Note GVRP will only add a port to a VLAN if the port is an 802.1q trunk port.
GARP/GVRP provides the following benefits:
• The administrator is not required to know ahead of time which VLANS should be configured on the
network.
• The administrator does not have to manually configure all VLANS on the network.
• It prunes unnecessary traffic if a VLAN goes down.
5.11.1 Running GARP/GVRP with STP
Anytime GARP /GVRP configures a VLAN or adds ports to a VLAN, this information needs to be propagated on all
other ports that are part of the active topology. If STP is disabled, this includes all ports, except the input port. If STP
is enabled, this includes all ports that are in the forwarding mode, except the input port.