Setting socket outgoing port number in Linux kernel

Question

I am trying to integrate multipath tcp (https://www.multipath-tcp.org/) into a project, and I would like to modify the source code in order to manually choose the outgoing socket port for a new mptcp subflow so that I can identify the packets going in and out within my application.

The address is created with:

inet_create(sock_net(meta_sk), &sock, IPPROTO_TCP, 1);

and bound:

sock.ops->bind(&sock, (struct sockaddr *)&loc_in, sizeof(struct sockaddr_in));

and then connected:

sock.ops->connect(&sock, (struct sockaddr *)&rem_in,
            sizeof(struct sockaddr_in), O_NONBLOCK);

My question is this: How can I manually set the outgoing port of a socket at kernel level, and/or where is the port set in this sequence of calls, so I can modify it?

Remy Lebeau · Accepted Answer · 2016-07-05 19:14:28Z

2

You would set the outgoing port in the loc_in structure that you use to bind() the socket to a local adapter/interface, eg:

struct sockaddr_in loc_in;
loc_in.sin_family = AF_INET;

// desired port...
loc_in.sin_port = htons(...);

// IP of desired adapter to connect() from...
loc_in.sin_addr.s_addr = inet_addr("...");

edited Jul 5, 2016 at 19:14

Remy Lebeau

609k36 gold badges516 silver badges875 bronze badges

answered Jul 5, 2016 at 15:53

4pie0

29.9k10 gold badges86 silver badges125 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

BeefSupreme Over a year ago

Thanks! Exactly what I needed.

Collectives™ on Stack Overflow

Setting socket outgoing port number in Linux kernel

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related