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Chapter 9 VLAN

GS2200-8/24 User’s Guide

level is significant and the default VID of the ingress port is given as the VID of the frame. Of the

4096 possible VIDs, a VID of 0 is used to identify priority frames and value 4095 (FFF) is reserved,

so the maximum possible VLAN configurations are 4,094.

Forwarding Tagged and Untagged Frames

Each port on the Switch is capable of passing tagged or untagged frames. To forward a frame from

an 802.1Q VLAN-aware switch to an 802.1Q VLAN-unaware switch, the Switch first decides where

to forward the frame and then strips off the VLAN tag. To forward a frame from an 802.1Q VLAN-

unaware switch to an 802.1Q VLAN-aware switch, the Switch first decides where to forward the

frame, and then inserts a VLAN tag reflecting the ingress port's default VID. The default PVID is

VLAN 1 for all ports, but this can be changed.

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.

9.1.2.1 Automatic VLAN Registration

GARP and GVRP are the protocols used to automatically register VLAN membership across switches.

GARP

GARP (Generic Attribute Registration Protocol) allows network switches to register and de-register

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.

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 Declarations are withdrawn by issuing a Leave message.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.

GVRP

GVRP (GARP VLAN Registration Protocol) is a registration protocol that defines a way for switches to

groups beyond the local Switch.

Please refer to the following table for common IEEE 802.1Q VLAN terminology.

TPID

2 Bytes

User Priority

3 Bits

CFI

1 Bit

VLAN ID

12 bits

Table 16 IEEE 802.1Q VLAN Terminology

VLAN PARAMETER TERM DESCRIPTION

VLAN Type Permanent VLAN This is a static VLAN created manually.

Dynamic VLAN This is a VLAN configured by a GVRP registration/

deregistration process.