Port-Based Virtual LANs (VLANs) and GVRP

GVRP

General Operation

When GVRP is enabled on a switch, the VID for any static VLANs configured on the switch is advertised (using BPDUs—Bridge Protocol Data Units) out all ports, regardless of whether a port is up or assigned to any particular VLAN. A GVRP-aware port on another device that receives the advertisements over a link can dynamically join the advertised VLAN.

A dynamic VLAN (that is, a VLAN learned through GVRP) is tagged on the port on which it was learned. Also, a GVRP-enabled port can forward an advertise­ ment for a VLAN it learned about from other ports on the same switch (internal source), but the forwarding port will not itself join that VLAN until an adver­ tisement for that VLAN is received through a link from another device (exter­ nal source) on that specific port

Operating Note: When a GVRP-aware port on a switch learns a VID through GVRP from another device, the switch begins advertising that VID out all of its ports except the port on which the VID was learned.

Core switch with static VLANs (VID= 1, 2, & 3). Port 2 is a member of VIDs 1, 2, & 3.

1.Port 2 advertises VIDs 1, 2, & 3.

2.Port 1 receives advertise­ ment of VIDs 1, 2, & 3 AND becomes a member of VIDs 1, 2, & 3.

3.Port 3 advertises VIDs 1, 2, & 3, but port 3 is NOT a member of VIDs 1, 2, & 3 at this point.

4.Port 4 receives advertise­ ment of VIDs 1, 2, & 3 AND becomes a member of VIDs 1, 2, & 3.

5.Port 5 advertises VIDs 1, 2, & 3, but port 5 is NOT a member of VIDs 1, 2, & 3 at this point.

Port 6 is statically configured to be a member of VID 3.

Switch 1

 

Switch 2

 

 

Switch 3

 

 

Static VLAN con-

 

 

 

GVRP On

 

GVRP On

 

 

GVRP On

 

 

figured End Device

 

 

 

 

 

 

 

 

(NIC or switch)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

with GVRP On

 

 

 

 

2

 

 

1

 

3

 

4

 

5

 

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

11.Port 2 receives advertisement of VID 3. (Port

2is already statically configured for VID 3.)

9.Port 3 receives advertise­ ment of VID 3 AND becomes a member of VID 3. (Still not a member of VIDs 1 & 2.)

10.Port 1 advertises VID 3.

7. Port 5 receives advertise­ 6. Port 6 advertises VID 3. ment of VID 3 AND becomes

a member of VID 3. (Still not a member of VIDs 1 & 2.)

8.Port 4 advertises VID 3.

Figure 11-24. .Example of Forwarding Advertisements and Dynamic Joining

Note that if a static VLAN is configured on at least one port of a switch, and that port has established a link with another device, then all other ports of that switch will send advertisements for that VLAN.

11-35