ZyXEL Communications GS 2200 Manual page 84

Chapter 9 VLAN
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.
TPID User Priority
2 Bytes 3 Bits
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 Declarations are withdrawn by issuing a Leave message.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
register necessary VLAN members on ports across the network. Enable this function to permit VLAN
groups beyond the local Switch.
Please refer to the following table for common IEEE 802.1Q VLAN terminology.
Table 16 IEEE 802.1Q VLAN Terminology
VLAN PARAMETER
VLAN Type
84
CFI VLAN ID
1 Bit 12 bits
TERM DESCRIPTION
Permanent VLAN This is a static VLAN created manually.
Dynamic VLAN This is a VLAN configured by a GVRP registration/
deregistration process.
GS2200-8/24 User's Guide