ZyXEL Communications 2002 Series Guide de l'utilisateur télécharger pdf (Page 47)

VES-1000 Series Ethernet Switch

General, Switch and IP Setup 4-9

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.

Each port on the switch is capable of receiving tagged or untagged frames. You can configure a VES-1000 Series

switch to receive only tagged or all frames on a port-by-port basis. If it is set to tagged-only on a port, then only

tagged frames are allowed to enter from that port and untagged frames are dropped; if set to all, then both tagged

and untagged frames are allowed to enter the switch. The VES-1000 Series switch does not alter the VID of a

frame if it is already tagged; however, when an untagged frame enters the switch, it is assigned the default port

VID (PVID) of the ingress (incoming) port. Thus a frame always has a VID inside the switch, regardless of

whether it is tagged or not on the wire. The default PVID is 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 (or multicast without IGMP snooping) 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 be members of multiple VID). 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.

Figure 4-6 Forwarding Tagged/Untagged Frames to 802.1Q VLAN Aware/Unaware Devices

4.2.7 IGMP Snooping

Traditionally, IP packets are transmitted in one of either two ways - Unicast (1 sender to 1 recipient) or Broadcast

(1 sender to everybody on the network). Multicast delivers IP packets to just a group of hosts on the network.

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ZyXEL Communications 2002 Series Guide de l'utilisateur Page 47