CODEWITHSUNDEEP
clinuxsocketstcp
user1415536
user1415536

Reputation: 266

Raw sockets linux

May be the question is a bit stupid, but I'll ask it. I read a lot about raw sockets in network, have seen several examples. So, basically with raw sockets it's possible to build own stack of headers, like stack = IP + TCP/UDP + OWN_HEADER. My question is, is it possible to get some kind of ready frame of first two(IP + TCP/UDP) from the linux kernel and then just append own header to them? The operating system in question is linux and the language is C.

I cannot find any function which can do such a thing, but may be I'm digging in a wrong direction.

Upvotes: 0

Views: 1373

Answers (3)

phenompbg
phenompbg

Reputation: 401

I don't think you understand what RAW sockets are for. With RAW sockets (s = socket (AF_INET, SOCK_RAW, IPPROTO_RAW)) you have to build everything above the physical layer yourself.

That means you build the IP header (if you want to build your protocol on top of IP of course), you could do your own thing here with AF_PACKET. And if you want TCP, you build the TCP header yourself, and add it to the IP header. In most cases when you use RAW sockets, this is where you would start building your own protocol in place of TCP or UDP, otherwise why use RAW Sockets in the first place? IF you wanted to build your own ICMP or SCTP implementation for example, you would use RAW Sockets.

If you really want to understand how this works I suggest building your own version of "ping" (ICMP echo request implementation, in other words). Its easy to do and easy to test and will force you to get your hands a little dirty.

The man pages cover this entire topic quite well if you ask me. Start at socket.

Upvotes: 1

Claudio
Claudio

Reputation: 10947

I would rely on existing protocols (i.e., UDP for best-effort and TCP for reliable) and encapsulate my own header inside them. In practice, this means embed your own protocol over a standard UDP/TCP connection. This way, you can use existing kernel and user-level tools.

If you want to do the other way around (i.e., UDP/TCP encapsulated in your own header) you have to design/implement your own protocol in the linux kernel, which is quite complicated.

Upvotes: 3

nos
nos

Reputation: 229108

No, that is not possible for raw sockets.

You either sit on top of TCP/UDP, in which case the IP stack takes care of the headers and the operation of the protocol(e.g. in the case of TCP how to slice up your data into segments),

So, if you want to add stuff on top of TCP or UDP, that's what a normal TCP or UDP socket is for.

Or you sit on top of IP, in which case it is your responsibility to craft whatever you want on top of IP - That's what a raw socket is for. Though in this case you can construct the IP header as well, or opt in to have the IP stack generate the IP header too.

Upvotes: 2

Related Questions