Panasonic NN46240-502 - Manual (Page 64)

Nortel Secure Router 8000 Series
Configuration - LAN Access and MAN Access 4 VLAN configuration
VLAN classification
Theoretically, you can classify VLANs in the following ways:
• Based on ports: The VLAN is classified based on the port numbers of a switch.
• Based on MAC addresses: The VLAN is classified based on the MAC addresses of
network interface cards.
• Based on the network layer protocol: For example, hosts running IP belong to one
VLAN, and those running internetwork packet exchange (IPX) belong to another VLAN.
• Based on the network address
The 802.1Q standard draft, issued by the IEEE in 1999, defines the standards for classifying
VLANs based on ports and MAC addresses.
VLAN frame formats
The IEEE 802.1Q standard modifies the Ethernet frame format. It adds a 4-byte 802.1Q tag
between the source MAC address and the protocol type fields, as shown in Figure 4-4.
Figure 4-4 VLAN frame format based on 802.1Q
Leader
Character
Destination
Address
Source
Address
802.1Q Tag
Type
PRI/
CFI
/VID
Length
/Type
Data
FCS
(CRC-32)
8 bytes 6 bytes 6 bytes 4 bytes 2 bytes 46-1517 bytes 4 bytes
The 802.1Q tag contains the following four fields:
• Type: It has two bytes, indicating the frame type. The value 0x8100 indicates an 802.1Q
tag frame, which is discarded by devices that do not support the 802.1Q standard.
• Priority (PRI): It has three bits, indicating the priority of a frame. It is used in Quality of
Service (QoS). The value ranges from 0 to 7.
• CFI: It has one bit, and is the abbreviated form of Canonical Format Indicator. It
indicates whether a MAC address is canonical and is used on token ring and Fiber
Distributed Digital Interface (FDDI).
• VLAN ID (VID): It has 12 bits and specifies the VLAN to which this frame belongs. In
the Secure Router 8000 Series, the VLAN ID 0 represents the default VLAN.
How a switch processes frames
A switch processes frames in three stages:
Step 1 The switch receives frames. Received frames can be VLAN frames with tags, or Ethernet
frames without tags. According to type and configuration of the receiving port, the switch
adds tags, discards the data frames, or processes the frames.
Step 2 The switch finds and forwards frames. According to the destination MAC address and VLAN
ID of the frames, the Layer 2 switch finds information about the VLAN configuration and
then determines to which port the frames should be sent.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 4-5