Friday, October 19, 2012

How data looks when we see it at different layers


What Data Looks Like on an Ethernet Network



An Ethernet frame has a 14 byte header, a data section, and a 4 byte trailer.
Ethernet header contains the address of the machine that should read the frame, the address of the machine that sent the frame, and the Ether Type
Ether Type is used to indicate which protocol is encapsulated in the payload of an Ethernet Frame.
0800 – IPv4, 0806 – ARP, 8035 – RARP, 8600 – IPv6
802.1Q tag
The IEEE 802.1Q tag is an optional 4-octet field that indicates Virtual LAN (VLAN) membership and IEEE 802.1p priority.
Payload Data
The minimum payload is 42 Bytes when 802.1Q tag is present and 46 Bytes when absent and the maximum payload is 1500 Bytes. Non-standard jumbo frames allow for larger maximum payload size
Frame check sequence (CRC)
The frame check sequence is a 4-octet cyclic redundancy check which allows detection of corrupted data within the entire frame.