The egress (outgoing) port(s) of a frame is determined on the combination of the destination MAC address and the VID of the frame. For a unicast frame, the egress port (based on the destination MAC address) must be a member of the VID, also; otherwise, the frame is blocked. A broadcast frame (or a multicast frame for a multicast group that is known by the system) is duplicated only on ports that are members of the VID (except the ingress port itself), thus confining the broadcast to a specific domain.
Whether to tag an outgoing frame depends on the setting of the egress port on an individual VLAN and port basis (remember that a port can belong to multiple VLANs). If the tagging on the egress port is enabled for the VID of a frame, then the frame is transmitted as a tagged frame; otherwise, it is transmitted as an untagged frame.
8.2 Automatic VLAN Registration
GARP and GVRP are the protocols used to automatically register VLAN membership across switches.
8.2.1 GARP
GARP (Generic Attribute Registration Protocol) allows network switches to register and deregister attribute values with other GARP participants within a bridged LAN. GARP is a protocol that provides a generic mechanism for protocols that serve a more specific application, for example, GVRP.
8.2.1.1 GARP Timers
Switches join VLANs by making a declaration. A declaration is made by issuing a Join message using GARP. Declarations are withdrawn by issuing a Leave message. A Leave All message terminates all registrations. GARP timers set declaration timeout values.
8.2.2 GVRP
GVRP (GARP VLAN Registration Protocol) is a registration protocol that defines a way for switches to register necessary VLAN members on ports across the network. Enable this function to permit VLANs groups beyond the local switch.
Please refer to the following table for common IEEE 802.1Q VLAN terminology.
Table 13 IEEE 802.1Q VLAN Terminology
VLAN PARAMETER | TERM | DESCRIPTION |
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|
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VLAN Type | Permanent VLAN | This is a static VLAN created manually. |
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|
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| Dynamic VLAN | This is a VLAN configured by a GVRP registration/ |
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| deregistration process. |
85 | Chapter 8 VLAN |