How to programmatically edit the routing table

Question

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

Answer 1

Check out SIOCADDRT/SIOCDELRT ioctls (Stevens' "Unix Network Programming" would be a good reference.)

Answer 2

I typed

man route

cause I know sometimes I can get a hint in the "see also" section for how to do the same thing programatically. I saw there was a man page on page 4 for "route" (route(4) was in the see also section). So tried

man 4 route

and it looked promising for doing what the route command can do programmitically.

Note I just noticed this is only for BSD systems. Here is a URL with the manpage http://www.manpagez.com/man/4/route/. This may or may not be helpful. Maybe you can google some of the stuff in here and add the word "linux".