ZyXEL Communications GS1350 Series User Manual page 122

The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for Ethernet switches. If a
frame received at an Ethernet port has a CFI set to 1, then that frame should not be forwarded as it is to
an untagged port. The remaining twelve bits define the VLAN ID, giving a possible maximum number of
4,096 VLANs. Note that user priority and VLAN ID are independent of each other. A frame with VID
(VLAN Identifier) of null (0) is called a 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 User Priority
2 Bytes 3 Bits
Fo rwa rding T a g g e d a nd Unta g g e d Fra m e s
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 Po rt VL AN T runking
Enable
VL AN T runking
that port. This is useful if you want to set up VLAN groups on end devices without having to configure the
same VLAN groups on intermediary devices.
Refer to the following figure. Suppose you want to create VLAN groups 1 and 2 (V1 and V2) on devices
A and B. Without
D and E; otherwise they will drop frames with unknown VLAN group tags. However, with
enabled on a port(s) in each intermediary switch you only need to create VLAN groups in the end
devices (A and B). C, D and E automatically allow frames with VLAN group tags 1 and 2 (VLAN groups
that are unknown to those switches) to pass through their VLAN trunking ports.
Port VLAN Trunking
Fig ure 96
9.1.2.2 VL AN Prio rity
At the time of writing, you can create static VLANs, Voice VLANs, MAC-based VLANs and Vendor ID-
based VLANs on the Switch when the VLAN type is set to
processes the VLAN rules in sequence. The sequence (priority) of the VLANs is:
Chapter 9 VLAN
CFI VLAN ID
1 Bit 12 bits
on a port to allow frames belonging to unknown VLAN groups to pass through
, you must configure VLAN groups 1 and 2 on all intermediary switches C,
VL AN T runking
GS1350 Series User's Guide
. When a packet is received, the Switch
802.1Q
122
VL AN T runking