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User’s Manual of
Adding an IEEE802.1Q Tag
Dest. Addr. | Src. Addr. | Length/E. type | Data | Old CRC |
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Original Ethernet
Dest. Addr.
Src. Addr.
E. type
Tag
Length/E. type
Data
New CRC
New Tagged Packet
Priority
CFI VLAN ID
■Port VLAN ID
Packets that are tagged (are carrying the 802.1Q VID information) can be transmitted from one 802.1Q compliant network device to another with the VLAN information intact. This allows 802.1Q VLAN to span network devices (and indeed, the entire network – if all network devices are 802.1Q compliant).
Every physical port on a switch has a PVID. 802.1Q ports are also assigned a PVID, for use within the switch. If no VLAN are defined on the switch, all ports are then assigned to a default VLAN with a PVID equal to 1. Untagged packets are assigned the PVID of the port on which they were received. Forwarding decisions are based upon this PVID, in so far as VLAN are concerned. Tagged packets are forwarded according to the VID contained within the tag. Tagged packets are also assigned a PVID, but the PVID is not used to make packet forwarding decisions, the VID is.
A switch port can have only one PVID, but can have as many VID as the switch has memory in its VLAN table to store them.
Because some devices on a network may be
■Default VLANs
The Switch initially configures one VLAN, VID = 1, called "default." The factory default setting assigns all ports on the Switch to the "default". As new VLAN are configured in
■Assigning Ports to VLANs
Before enabling VLANs for the switch, you must first assign each port to the VLAN group(s) in which it will participate. By default all ports are assigned to VLAN 1 as untagged ports. Add a port as a tagged port if you want it to carry traffic for one or more
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