If I have a packet sending out from a LAN, can I find out which computer in the LAN sending out this packet?

Question

If I have a packet sending out from a LAN, can I find out which computer in the LAN sending out this packet?

Does this out going packet contains source information such as MAC address?

Answer 1

http://www.ietf.org/rfc/rfc2464.txt

Read section 3, "Frame Format". Each frame has a source Ethernet address, aka MAC address. All you need to do is read the memory at that offset. This is for IPv6, check out IPv4 here: http://www.ietf.org/rfc/rfc791.txt (see section 3, "Specification")