Final answer:
The function htonl() is used to convert a long integer to the network byte order, ensuring consistent data interpretation across different endianness in TCP/IP networks.
Step-by-step explanation:
The function used to convert a long integer to the network byte order is htonl(). This stands for "Host TO Network Long" and is used within network programming to ensure that the data sent over a network is understood by computers with different endianness. When a computer sends data to a computer with a different byte order, it could lead to incorrect data interpretation unless this conversion is done. Using htonl() properly converts the byte order from the host's endianness to the network's big-endian format, which is the standard used in TCP/IP networks.