ZyXEL Communications Plumbing Product metrogigabit switch User Manual

Chapter 9 VLAN

MGS3700-12C User’s Guide

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. 

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

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. 

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 Declarations are withdrawn by issuing a Leave 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 (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 VLAN groups beyond the local Switch.