How do I make an outgoing socket to a SPECIFIC network interface?

Question

I have a server with two different network interfaces, each with a different IP address. How can I create a socket so it\'ll go out a specific IP address?

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Answer 1

Just a little note - what I really needed is to bind to a specific IP, and just for the sake of completeness, the solution is to bind the socket after creation. Source in python:

import socket
s = socket.socket()
s.bind(("127.0.0.1", 0))
s.connect(("321.12.131.432", 80))

Answer 2

You can certainly bind a socket to a specific device.

I don't know how to do it in python, but using the berkeley socket api (in C) you need to call setsockopt(), using the option SO_BINDTODEVICE.

You pass in an interface descriptor, which is of type struct ifreq. Ideally you would get the contents of the interface descriptor by using ioctl(), and requesting SIOCGIFINDEX - passing the name of the interface (eg. eth0) as an argument.

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edit: Just did a quick search and found this documentation of the socket methods in python. setsockopt() is amongst them.

Answer 3

import socket
s = socket.socket()
s.bind((get_ip_address('eth0'), 0))

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