CODEWITHSUNDEEP
linuxtcp
kagali-san
kagali-san

Reputation: 3082

Linux: how to send TCP packet from specific port?

How to open a raw socket for sending from specific TCP port? I want to have all my connections always go from a range of ports below ephemerals.

Upvotes: 3

Views: 5687

Answers (2)

MarkR
MarkR

Reputation: 63538

Making a tcp connection using raw sockets is somewhere between difficult and impossible; you'd need to implement the entire tcp protocol in your program AND also stop the kernel from sending its own replies to the packets (if the kernel has IP bound on that address on that interface).

This is probably not what you want. However, if you did want it, it is trivial to send tcp frames with any source port you want, as you get to specify it in the tcp header, which of course, if you're implementing your own TCP layer, you'll need to understand.

Upvotes: 1

thkala
thkala

Reputation: 86333

If you are using raw sockets, then just fill in the correct TCP source port in the packet header.

If, instead, you are using the TCP socket interface (socket(), connect() and friends), then you can set the source port by calling the bind() system call for the client socket - exactly as you would to set the listening port for the server socket.

Upvotes: 6

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