Forwarding Tagged And Untagged Frames; Automatic Vlan Registration; Garp - ZyXEL Communications Multi-service Access Platform MSAP2000 User Manual

MSAP2000 AAMS User's Guide
priority frame, meaning that only the priority 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
2 Bytes
The MSAP2000 AAMS handles up to 4094 VLANs (VIDs 1-4094). The switch
accepts incoming frames with VIDs 1-4094.

8.2.1 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 by the destination 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.

8.3 Automatic VLAN Registration

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

8.3.1 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.
User Priority
CFI
1 Bits
3 Bits
85
VLAN ID
12 bits