ZyXEL Communications P-660H-T1 v3s, Руководство пользователя

Страница: 136 / 272

Chapter 12 802.1Q/1P
P-660H-T1v3s User’s Guide
136
IEEE 802.1Q Tagged VLAN
Tagged VLAN uses an explicit tag (VLAN ID) in the MAC header to identify the
VLAN membership of a frame across bridges - they are not confined to the device
on which they were created. The VLAN ID associates a frame with a specific VLAN
and provides the information that devices need to process the frame across the
network.
PVC
A virtual circuit is a logical point-to-point circuit between customer sites.
Permanent means that the circuit is preprogrammed by the carrier as a path
through the network. It does not need to be set up or torn down for each session.
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 device to an 802.1Q VLAN-unaware
device, the P-660H-T1v3s first decides where to forward the frame and then strips
off the VLAN tag. To forward a frame from an 802.1Q VLAN-unaware device to an
802.1Q VLAN-aware switch, the P-660H-T1v3s 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.
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.