ZyXEL Communications IES-1248 VDSL-SWITCH User Manual page 126

IES-1248 User's Guide
12.2.1 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.
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. For a broadcast frame, it is duplicated only on ports (except the
ingress port itself) that are members of the VID, 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.
12.2.2 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Declarations are withdrawn by issuing a Leave message.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 VLANs groups beyond the
local switch.
Please refer to the following table for common GARP terminology.
12-2 VLAN