The protocol parameter in socket and WSASocket is an identifier that establishes a network type and a method for identifying the various transport protocols that run on the network. Unlike IP, IPX does not use a single protocol value for selecting a transport stack. Since there is no network requirement to use a specific value for each transport protocol, we are free to assign them in a manner convenient for Windows Sockets applications. We avoid values 0..255 in order to avoid collisions with the corresponding PF_INET protocol values.
| Name | Value | Socket Types | Description |
|---|---|---|---|
| Reserved | 0-255 | Reserved for PF_INET protocol values. | |
| NSPROTO_IPX | 1000 - 1255 | SOCK_DGRAM SOCK_RAW | Datagram service for IPX. |
| NSPROTO_SPX | 1256 | SOCK_STREAM SOCK_SEQPKT | Reliable packet exchange using fixed-sized packets. |
When NSPROTO_SPX is specified, the SPX II protocol will automatically be utilized if both endpoints are capable of doing so.