ZyXEL Communications IES-708-22A - Manual (Page 140)

Chapter 17 VLAN
IES-708-22A User’s Guide
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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.
The IES-708-22A handles up to 4094 VLANs (VIDs 1-4094). The device accepts incoming
frames with VIDs 1-4094.
17.2.1 Forwarding Tagged and Untagged Frames
Each port on the device 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 IES-708-22A
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 IES-708-22A
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 a per-VLAN,
per-port basis (recall 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.
17.3 VLAN Status Screen
To open this screen, click Advanced Application > VLAN.
TPID
2 Bytes
User Priority
3 Bits
CFI
1 Bit
VLAN ID
12 bits