| 0 | HOPOPT | IPv6 Hop-by-Hop Option |
| 1 | ICMP | Internet Control Message |
| 2 | IGMP | Internet Group Management |
| 3 | GGP | Gateway-to-Gateway |
| 4 | IP | IP in IP (encapsulation) |
| 5 | ST | Stream |
| 6 | TCP | Transmission Control Protocol |
| 8 | EGP | Exterior Gateway Protocol |
| 9 | IGP | any private interior gateway |
| 10 | BBN-RCC-MON | BBN RCC Monitoring |
| 11 | NVP-II | Network Voice Protocol |
| 17 | UDP | User Datagram |
| 18 | MUX | Multiplexing |
| 19 | DCN-MEAS | DCN Measurement Subsystems |
| 20 | HMP | Host Monitoring |
| 21 | PRM | Packet Radio Measurement |
| 22 | XNS-IDP | XEROX NS IDP |
| 27 | RDP | Reliable Data Protocol |
| 28 | IRTP | Internet Reliable Transaction |
| 29 | ISO-TP4 | ISO Transport Protocol Class 4 |
| 30 | NETBLT | Bulk Data Transfer Protocol |
| 31 | MFE-NSP | MFE Network Services Protocol |
| 32 | MERIT-INP | MERIT Internodal Protocol |
| 34 | 3PC | Third Party Connect Protocol |
| 37 | DDP | Datagram Delivery Protocol |
| 39 | TP++ | TP++ Transport Protocol |
| 40 | IL | IL Transport Protocol |
| 46 | RSVP | Reservation Protocol |
| 47 | GRE | General Routing Encapsulation |
| 48 | MHRP | Mobile Host Routing Protocol |
| 50 | ESP | Encapsulation Security Payload |
| 51 | AH | Authentication Header |
| 53 | SWIPE | IP with Encryption |
| 54 | NHRP | NBMA Next Hop Resolution Protocol |
| 61 | | any host internal protocol |
| 63 | | any local network |
| 64 | SAT-EXPAK | SATNET and Backroom EXPAK |
| 65 | KRYPTOLAN | Kryptolan |
| 66 | RVD | MIT Remote Virtual Disk Protocol |
| 68 | | any distributed file system |
| 69 | SAT-MON | SATNET Monitoring |
| 70 | VISA | VISA Protocol |
| 75 | PVP | Packet Video Protocol |
| 80 | ISO-IP | ISO Internet Protocol |
| 84 | TTP | TTP |
| 85 | NSFNET-IGP | NSFNET-IGP |
| 86 | DGP | Dissimilar Gateway Protocol |
| 87 | TCF | TCF |
| 88 | EIGRP | EIGRP |
| 91 | LARP | Locus Address Resolution Protocol |
| 92 | MTP | Multicast Transport Protocol |
| 93 | AX.25 | AX.25 Frames |
| 94 | IPIP | IP-within-IP Encapsulation Protocol |
| 95 | MICP | Mobile Internetworking Control Pro. |
| 97 | ETHERIP | Ethernet-within-IP Encapsulation |
| 98 | ENCAP | Encapsulation Header |
| 99 | | any private encryption scheme |
| 100 | GMTP | GMTP |
| 115 | L2TP | Layer Two Tunneling Protocol |
| 255 | | Reserved |