> But this has chances to fail.  Why not do it the other way around, which
> will be completely safe?  I.e.:
> 
> #ifndef IRIX
> #include <netinet/ip_var.h>
> #endif
> #include <netinet/if_ether.h>
> 
> (Replace IRIX by the appropriate macro.)

well, it is not an IRIX-specific problem. Rather it is a problem of
netinet/ip_var.h being included twice on anything but Linux
(see include/libnet.h).
Maybe I will first look into whether the problem still exists with the
current stable version of libnet.

-- 
Georg Schwarz    http://home.pages.de/~schwarz/
 georg.schwarz@freenet.de  +49 178 8545053