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Chapter 49: GARP VLAN Registration Protocol
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Without GVRP, you would have to manually add the Sales VLAN to switch
#2. But with GVRP, the VLAN is added automatically. Here is how GVRP
would resolve the problem in the example.
1. Port 1 on switch #1 sends to port 2 on switch #2 a PDU that contains
the VIDs of all the VLANs on the switch, including VID 11 for the Sales
VLAN.
2. Switch #2 examines the PDU it receives on port 2 and notes that it
does not have a VLAN with a VID 11. In response, it creates the VLAN
as a dynamic GVRP VLAN, assigning it a VID 11 and the name
GVRP_VLAN_11. (The name of a dynamic GVRP VLAN has the prefix
“GVRP_VLAN_”, followed by the VID number.) The switch then adds
port 2, the port that received the PDU, as a tagged member of the
VLAN.
3. Switch #2 sends a PDU from port 3 containing all the VIDs of the
VLANs on the switch, including the new GVRP_VLAN_11 with its VID
of 11. (Note that port 3 is not yet a member of the VLAN. Ports are
added to VLANs when they receive PDUs from other network devices,
not when they transmit PDUs.)
4. Switch #3 receives the PDU on port 4 and, after examining it, notes
that one of the VLANs on switch #2 has the VID 11, which matches the
VID of an already existing VLAN on the switch. So it does not create
the VLAN because it already exists. It then determines whether the
port that received the PDU, in this case port 4, is a member of the
VLAN. If it is not a member, it automatically adds the port to the VLAN
as an tagged dynamic GVRP port. If the port is already a member of
the VLAN, then no change is made.
5. Switch #3 sends a PDU out port 4 to switch #2.
6. Switch #2 receives the PDU on port 3 and then adds the port as a
tagged dynamic GVRP port to the dynamic GVRP_VLAN_11 VLAN.
There is now a communications path for the end nodes of the Sales VLAN
on switches #1 and #3. GVRP created the new GVRP_VLAN_11 dynamic
GVRP VLAN with a VID of 11 on switch #2 and added ports 2 and 3 to the
VLAN as tagged dynamic GVRP ports.