zkNetinetIn.h is a portable wrapper for the POSIX header <netinet/in.h>. It is part of the libzk library because <netinet/in.h> doesn't exist in Standard C.

zkNetinetIn.h - Supported Macros from <netinet/in.h>
Macro Description
IPPROTO_IP Dummy for IP.
IPPROTO_ICMP Control message protocol.
IPPROTO_TCP TCP.
IPPROTO_UDP User datagram protocol.
INADDR_ANY Local host address.
INADDR_BROADCAST Broadcast address.

zkNetinetIn.h - Supported Types from <netinet/in.h>
Type Description
in_port_t An unsigned integral type of exactly 16 bits.
in_addr_t An unsigned integral type of exactly 32 bits.
struct in_addr, with members:  
in_addr_t s_addr
 
struct sockaddr_in, with members:  
sa_family_t    sin_family
 
in_port_t      sin_port
 
struct in_addr sin_addr
 
unsigned char  sin_zero[8]