Altera Triple Speed Ethernet MegaCore Function - Manual (Page 193)

fields. VLAN tagging is defined by the IEEE Standard 802.1Q. VLAN tagging can identify and separate many
groups' network traffic from each other in enterprise and metro networks. Each VLAN group can consist
of many users with varied MAC address in different geographical locations of a network. VLAN tagging
increases and scales the network performance and add privacy and safety to various groups and customers'
network traffic.
VLAN tagged frames have a maximum length of 1522 bytes, excluding the preamble and the SFD fields.
Figure A-2: VLAN Tagged MAC Frame Format
7 octets PREAMBLE
1 octet SFD
6 octets DESTINATION ADDRESS
6 octets SOURCE ADDRESS
2 octets CLIENT LENGTH/TYPE
PAYLOAD DATA
0..42 octets PAD
4 octets FRAME CHECK SEQUENCE
EXTENSION (half duplex only)
Frame length
2 octets
2 octets
VLAN info
LENGTH/TYPE (VLAN Tag 0x8100)
0..1500/9600 octets
In metro Ethernet applications, which require more scalability and security due to the sharing of an Ethernet
link by many service providers, MAC frames can be tagged with two consecutive VLAN tags (stacked VLAN).
Stacked VLAN frames contain an additional 8-byte field between the source address and client length/type
fields, as illustrated.
Figure A-3: Stacked VLAN Tagged MAC Frame Format
7 octets PREAMBLE
1 octet SFD
6 octets DESTINATION ADDRESS
6 octets SOURCE ADDRESS
2 octets
PAYLOAD DATA
0..38 octets PAD
4 octets FRAME CHECK SEQUENCE
Frame length
2 octets
2 octets
VLAN info
Stacked VLANs
2 octets
2 octets
VLAN info
EXTENSION (half duplex only)
CLIENT LENGTH/TYPE
LENGTH/TYPE (VLAN Tag 0x8100)
LENGTH/TYPE (VLAN Tag 0x8100)
0..1500/9600 octets
Ethernet Frame Format Altera Corporation
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VLAN and Stacked VLAN Frame Format A-2
2014.06.30