This is just a summary of the more common assignments. See RFC 1700 for the complete list.
| Decimal | Hex | Keyword | Protocol |
| 0 | 0 | Reserved | |
| 1 | 1 | ICMP | Internet Control Message |
| 6 | 6 | TCP | Transmission Control |
| 8 | 8 | EGP | Exterior Gateway Protocol |
| 9 | 9 | IGP | any private interior gateway |
| 17 | 11 | UDP | User Datagram |
| 46 | 2E | RSVP | Reservation Protocol |
| 47 | 2F | GRE | General Routing Encapsulation |
| 50 | 32 | SIPP-ESP | SIPP Encap Security Payload |
| 51 | 33 | SIPP-AH | SIPP Authentication Header |
| 88 | 58 | (E)IGRP | (Exterior) Interior Gateway Routing Protocol |
| 101-254 | 65-FE | Unassigned | |
| 255 | FF | Reserved |
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