Sunday 10 June 2012

Ethernet Format decided by two byte field in Ethernet Header

In Ethernet header we have different type of Ethernet headers like Ethernet-II, 802.3, 802.3 with 802.2 LLc,

802.3 with 802.2 and SNAP etc. To decide which format it is following the two byte field is checked after

Destination and source address of 802.3 header. If the value lies in range of 0x0000-0x05DC (1500 in

decimal) the value indicated length other wise if it is greater than 0x05DC it is Ethertype for Ethernet-II frame.

Like STP frames has length field in format : 802.3 (length) +LLC+STP

Normal ICMP frames has: Ethernet-II (ethertype-0800)+IP+ICMP