TCP/IP Filtering in WINNT Protocol codes

Microsoft enables the TCP/IP filtering function at the protocol level, only allowing certain protocols to be accepted by the machine. According to the OS error pop-up, these protocols are defined by numbers ranging from 0 to 256, however, I am unable to find any documentation on the number assignments. I have tried Tech Net, the Microsoft Knowledge base and every book on WINNT and TCP/IP that I could find, to no avail. Does anyone have this information to share? Thank You! Mike@portergroupinc.com