I am writing a daemon running on an embedded platform that needs to change the default route of the device according to which interface it is connecting on at a given time. How can I do this programatically? I know I can use system(“route del default && route add default gateway blah”); etc but is there a more direct way?
UPDATE: I solved my particular problem by discovering a patch to pppd that allows a replacedefaultroute option. The patch also includes code for programmatically modifying the routing table. It is included in this gentoo bug report http://bugs.gentoo.org/227321
Check out SIOCADDRT/SIOCDELRT ioctls (Stevens’ “Unix Network Programming” would be a good reference.)