How do I send UDP packet from a specific interface on Linux?

c linux sockets udp

13,250

Solution 1

You can bind a socket to a specific interface by using the SO_BINDTODEVICE socket option, however this requires root privileges.

Alternately, you can set the IP_PKTINFO option, and use sendmsg for sending, setting the in_pktinfo's ipi_ifindex to the index of your interface.

Solution 2

Use bind. You cannot send UDP packets via an interface that does not have an IP address, because UDP uses the Internet Protocol and the Internet Protocol requires an IP address.

13,250

jackhab

Updated on May 14, 2022

Comments

jackhab about 2 years

How do I send UDP packet from a specific interface on Linux using C? Should I use bind? Is it possible to send UDP from the interface not having IP address?

Thanks.
nategoose over 13 years

Unless you send them as raw packets.
Oswald over 13 years

@nategoose That would be cheating.
jackhab over 13 years

Bind does not help. The source IP of the UDP packet is correct (i.e. it's the IP of the interface I'm trying to send from) but the packet itself goes from the default interface.
Hasturkun over 13 years

Wouldn't that only work for multicast? (also, appears to require an address)
Hasturkun over 13 years

@Jack: You probably have a misconfigured routing table.
Hi-Angel over 9 years

Don't you know: is it a crossplatform way? E.g. would it work this way on Windows®?
Hasturkun over 9 years

@Hi-Angel: I haven't tried it, but apparently you can use the IPPROTO_IP IP_UNICAST_IF socket option on Windows. This option takes an interface index, and should also work on current Linux systems (was added in 2012 and is present in Linux v3.4).
Hi-Angel over 9 years

Hmm, interesting… I didn't found a mention about the option in GNU/Linux docs, but found a short note that it was added to help WINE project. I hope the WINE project aware of it :D
Hi-Angel over 9 years

Okay, I found a mails when a wine developer requested the feature, and some patch, possibly from wine developer too. But about was it implemented it the WINE or not, I found only this patch. Not sure what it does, but I am suppose that it checks if the linux kernel defined but IP_UNICAST_IF not, so fall back to old implementation. If suppose that WINE developers uses up-to-date kernel, then in all the new WINE versions used the real kernel option.
Joseph Wahba over 7 years

Could you please have a look on my question ? stackoverflow.com/questions/41192809/…
Joseph Wahba over 7 years

Could you please have a look on my question ? stackoverflow.com/questions/41192809/…
Compholio almost 3 years

Yes, I implemented IP_UNICAST_IF for Wine and it's been supported since Linux 3.3.