Manpages - ares_set_local_dev.3

ares_set_local_dev - Bind to a specific network device when creating sockets.

  #include <ares.h>

  void ares_set_local_dev(ares_channel channel, const char* local_dev_name)

The ares_set_local_dev function causes all future sockets to be bound to this device with SO_BINDTODEVICE. This forces communications to go over a certain interface, which can be useful on multi-homed machines. This option is only supported on Linux, and root privileges are required for the option to work. If SO_BINDTODEVICE is not supported or the setsocktop call fails (probably because of permissions), the error is silently ignored.

*ares_set_local_ip4*(3) *ares_set_local_ip6*(3)

This function was added in c-ares 1.7.4

Ben Greear