Legacy Document

Important: The information in this document is obsolete and should not be used for new development.

Inside Macintosh: Networking With Open Transport / Part 2 - Open Transport Reference: Chapter 29 - TCP/IP Services Reference / Options

Protocol Levels
The protocol level specifies the protocol to which the option applies. You specify the protocol level in the level field of the TOption structure when you specify an option.
enum {
   INET_IP  = 0x0,   /* IP */
   INET_TCP = 0x06,  /* TCP */
   INET_UDP = 0x11   /* UDP */
};