Raw IP packets on Linux

Mike Ayers mike.ayers at tumbleweed.com
Sun Aug 15 09:09:10 CEST 2004


Mike Ayers <mike.ayers <at> tumbleweed.com> writes:

> What am I getting wrong here?   What address type does this socket expect?

After further review, I find that AF_PACKET wants addresses that contain the
interface and protocol number.  You can also specify an ethernet address, but it
will be ignored (in fact, you can only specify a subset of ethernet addresses,
as the address argument is parsed as 's').

Quick summary: socket( AF_PACKET, SOCK_DGRAM ) is useless.

Workaround: use socket( AF_PACKET, SOCK_RAW ) and create your own ethernet
headers, which (provided you're using true ethernet, which most of us are), is
just the 6 byte ethernet destination address followed by the 6 byte ethernet
source address (.i.e your own), followed by 0x0800 (IP) in two bytes.  Really
pretty simple if you're already using raw sockets, eh?


     HTH,

/|/|ike





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