Confused about the header size for a Ethernet frame
ethernet, frame, header, lan
Solution
A regular 802.3/Eth-II ethernet frame doesn't carry VLAN info. 802.1Q can carry VLAN (and QoS) info over to the receiving end.
If the ethertype is 0x8100 then you got yourself an 802.1Q tag which is another 4 bytes in addition to the 14 bytes (dmac+smac+type).
See wikipedia for reference. http://en.wikipedia.org/wiki/Ethernet_frame
EDIT:
Regular Eth-II/802.3 has a total length of:
dmac(6)+smac(6)+etype(2)+payload(1500)+crc(4) = 1518 bytes
For the case of Eth-II/802.3 with 802.1Q tagging:
dmac(6)+smac(6)+8100(2)+vlan/Qos(2)+etype(2)+payload(1500)+crc(4) = 1522 bytes
Problem
I was researching a few things about `VLANs` and came across the `VLAN tag` and also the headers. If we have a MTU for a standard `802.3 Ethernet frame` (1518 bytes) what is included in the header `802.3`? Also how do we calculate the header length for that? What is the difference between `802.3 and 802.1q`? I know that the VLAN tag requires extra bytes but how to calculate how many bytes needed to the `802.1q VLAN tag`? Thanks in advance