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PowerConnect B-Series FCX Configuration Guide 435
53-1002266-01
VLAN overview
13
FIGURE 89 Packet containing a Dell 802.1Q VLAN tag
If you configure a VLAN that spans multiple devices, you need to use tagging only if a port
connecting one of the devices to the other is a member of more than one port-based VLAN. If a port
connecting one device to the other is a member of only a single port-based VLAN, tagging is not
required.
If you use tagging on multiple devices, each device must be configured for tagging and must use
the same tag value. In addition, the implementation of tagging must be compatible on the devices.
The tagging on all Dell PowerConnect devices is compatible with other Dell PowerConnect devices.
Figure 90 shows an example of two devices that have the same Layer 2 port-based VLANs
configured across them. Notice that only one of the VLANs requires tagging.
Untagged Packet Format
6 bytes
Destination
Address
6 bytes
Source
Address
2 bytes
Type
Field
Up to 1500 bytes
Data Field
4 bytes
CRC
Ethernet II
IEEE 802.3
802.1q Tagged Packet Format
4 bytes
802.1q
Tag
Ethernet II with 802.1q tag
IEEE 802.3 with 802.1q tag
Tag Protocol Id (TPID)
Octet 1
Octet 2
802.1p
(3 bits)
VLAN ID (12 bits)
Octet 4
1
23
45
6
78
6 bytes
Destination
Address
6 bytes
Source
Address
2 bytes
Length
Field
Up to 1496 bytes
Data Field
4 bytes
CRC
6 bytes
Destination
Address
6 bytes
Destination
Address
6 bytes
Source
Address
6 bytes
Source
Address
4 bytes
802.1q
Tag
2 bytes
Type
Field
2 bytes
Length
Field
Up to 1500 bytes
Data Field
Up to 1496 bytes
Data Field
4 bytes
CRC
4 bytes
CRC