ifunit - undefined reference

Hi,
I'm working on QNx4.25, watcom C compiler 10.6, tcpip stack v5.0
I am doing a porting work to qnx.
In regards to that i would like to get information on ifunit().
ifunit() is a function which will map the interface name with interface
pointer(struct ifnet *).

The program which i am porting is in user address space. On compilation
it gives me error message
ifunit- undefined reference.

The prototype (in /usr/includ/net/if.h ) goes like this 
struct ifnet *ifp;
struct ifnet *ifunit (char *ifname) ;

pls give me tip for solving this. Waiting for it, since this has to be
fixed very soon.
Thanks in advance
Divakar



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