Summary: We can't port "Debian netcat" to OS X without definining this. Who knows, perhaps someday there will be a Debian GNU/Darwin. Contributor: Loic Fosse <fosse@gostai.com> Index: netcat-1.10/netcat.c =================================================================== --- netcat-1.10.orig/netcat.c 2008-01-20 22:57:53.000000000 -0500 +++ netcat-1.10/netcat.c 2008-01-20 23:07:25.000000000 -0500 @@ -86,6 +86,10 @@ #include <unistd.h> #endif +#ifndef SOL_IP +# define SOL_IP IPPROTO_IP +#endif + /* handy stuff: */ #define SA struct sockaddr /* socket overgeneralization braindeath */ #define SAI struct sockaddr_in /* ... whoever came up with this model */