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IXP400 Software
Access-Layer Components: Ethernet Database (IxEthDB) API
Programmer’s Guide IXP400 Software Version 2.0 April 2005
Document Number: 252539, Revision: 007 163
10.3.4.1 Background – VLAN Data in Ethernet Frames
According to IEEE802.3, an untagged or normal Ethernet frame has the fields listed in Table 25.
The
Length/Type field is differentiated by whether its numerical value is greater than or equal to
0x600. If it is greater than or equal to 0x600, the field is interpreted as Type, which additionally
implies that there is no LLC/SNAP header in the frame. Otherwise, the field is interpreted as
Length, i.e. the number of bytes in the
MAC client data field. In this case, it is also implied that the
first field in the
MAC client data field is an LLC/SNAP header.
Table 25. Untagged MAC Frame Format
012345678910111213
Destination address Source address
Length/
Type
MAC client data and pad (46–
1500 bytes)
FCS
Table 26. VLAN Tagged MAC Frame Format
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Destination address Source address
VLAN
TPID
VLAN
TCI
Length/
Type
MAC client data and pad
(46–1500 bytes)
FCS