В интернет-протоколе версии 4 (IPv4) [RFC791] есть поле под названием "Протокол" для определения протокола следующего уровня. В этом 8-битном поле указывается номер протокола из таблицы ниже. Актуальность таблицы: 26.02.2021

Decimal	Keyword	Protocol	Reference
0	HOPOPT	IPv6 Hop-by-Hop Option	[RFC8200]
1	ICMP	Internet Control Message	[RFC792]
2	IGMP	Internet Group Management	[RFC1112]
3	GGP	Gateway-to-Gateway	[RFC823]
4	IPv4	IPv4 encapsulation	[RFC2003]
5	ST	Stream	[RFC1190][RFC1819]
6	TCP	Transmission Control	[RFC793]
7	CBT	CBT	[Tony_Ballardie]
8	EGP	Exterior Gateway Protocol	[RFC888][David_Mills]
9	IGP	any private interior gateway (used by Cisco for their IGRP)	[Internet_Assigned_Numbers_Authority]
10	BBN-RCC-MON	BBN RCC Monitoring	[Steve_Chipman]
11	NVP-II	Network Voice Protocol	[RFC741][Steve_Casner]
12	PUP	PUP	[Boggs, D., J. Shoch, E. Taft, and R. Metcalfe, "PUP: An Internetwork Architecture", XEROX Palo Alto Research Center, CSL-79-10, July 1979; also in IEEE Transactions on Communication, Volume COM-28, Number 4, April 1980.][[XEROX]]
13	ARGUS (deprecated)	ARGUS	[Robert_W_Scheifler]
14	EMCON	EMCON	[<mystery contact>]
15	XNET	Cross Net Debugger	[Haverty, J., "XNET Formats for Internet Protocol Version 4", IEN 158, October 1980.][Jack_Haverty]
16	CHAOS	Chaos	[J_Noel_Chiappa]
17	UDP	User Datagram	[RFC768][Jon_Postel]
18	MUX	Multiplexing	[Cohen, D. and J. Postel, "Multiplexing Protocol", IEN 90, USC/Information Sciences Institute, May 1979.][Jon_Postel]
19	DCN-MEAS	DCN Measurement Subsystems	[David_Mills]
20	HMP	Host Monitoring	[RFC869][Bob_Hinden]
21	PRM	Packet Radio Measurement	[Zaw_Sing_Su]
22	XNS-IDP	XEROX NS IDP	["The Ethernet, A Local Area Network: Data Link Layer and Physical Layer Specification", AA-K759B-TK, Digital Equipment Corporation, Maynard, MA. Also as: "The Ethernet - A Local Area Network", Version 1.0, Digital Equipment Corporation, Intel Corporation, Xerox Corporation, September 1980. And: "The Ethernet, A Local Area Network: Data Link Layer and Physical Layer Specifications", Digital, Intel and Xerox, November 1982. And: XEROX, "The Ethernet, A Local Area Network: Data Link Layer and Physical Layer Specification", X3T51/80-50, Xerox Corporation, Stamford, CT., October 1980.][[XEROX]]
23	TRUNK-1	Trunk-1	[Barry_Boehm]
24	TRUNK-2	Trunk-2	[Barry_Boehm]
25	LEAF-1	Leaf-1	[Barry_Boehm]
26	LEAF-2	Leaf-2	[Barry_Boehm]
27	RDP	Reliable Data Protocol	[RFC908][Bob_Hinden]
28	IRTP	Internet Reliable Transaction	[RFC938][Trudy_Miller]
29	ISO-TP4	ISO Transport Protocol Class 4	[RFC905][<mystery contact>]
30	NETBLT	Bulk Data Transfer Protocol	[RFC969][David_Clark]
31	MFE-NSP	MFE Network Services Protocol	[Shuttleworth, B., "A Documentary of MFENet, a National Computer Network", UCRL-52317, Lawrence Livermore Labs, Livermore, California, June 1977.][Barry_Howard]
32	MERIT-INP	MERIT Internodal Protocol	[Hans_Werner_Braun]
33	DCCP	Datagram Congestion Control Protocol	[RFC4340]
34	3PC	Third Party Connect Protocol	[Stuart_A_Friedberg]
35	IDPR	Inter-Domain Policy Routing Protocol	[Martha_Steenstrup]
36	XTP	XTP	[Greg_Chesson]
37	DDP	Datagram Delivery Protocol	[Wesley_Craig]
38	IDPR-CMTP	IDPR Control Message Transport Proto	[Martha_Steenstrup]
39	TP++	TP++ Transport Protocol	[Dirk_Fromhein]
40	IL	IL Transport Protocol	[Dave_Presotto]
41	IPv6	IPv6 encapsulation	[RFC2473]
42	SDRP	Source Demand Routing Protocol	[Deborah_Estrin]
43	IPv6-Route	Routing Header for IPv6	[Steve_Deering]
44	IPv6-Frag	Fragment Header for IPv6	[Steve_Deering]
45	IDRP	Inter-Domain Routing Protocol	[Sue_Hares]
46	RSVP	Reservation Protocol	[RFC2205][RFC3209][Bob_Braden]
47	GRE	Generic Routing Encapsulation	[RFC2784][Tony_Li]
48	DSR	Dynamic Source Routing Protocol	[RFC4728]
49	BNA	BNA	[Gary Salamon]
50	ESP	Encap Security Payload	[RFC4303]
51	AH	Authentication Header	[RFC4302]
52	I-NLSP	Integrated Net Layer Security TUBA	[K_Robert_Glenn]
53	SWIPE (deprecated)	IP with Encryption	[John_Ioannidis]
54	NARP	NBMA Address Resolution Protocol	[RFC1735]
55	MOBILE	IP Mobility	[Charlie_Perkins]
56	TLSP	Transport Layer Security Protocol using Kryptonet key management	[Christer_Oberg]
57	SKIP	SKIP	[Tom_Markson]
58	IPv6-ICMP	ICMP for IPv6	[RFC8200]
59	IPv6-NoNxt	No Next Header for IPv6	[RFC8200]
60	IPv6-Opts	Destination Options for IPv6	[RFC8200]
61		any host internal protocol	[Internet_Assigned_Numbers_Authority]
62	CFTP	CFTP	[Forsdick, H., "CFTP", Network Message, Bolt Beranek and Newman, January 1982.][Harry_Forsdick]
63		any local network	[Internet_Assigned_Numbers_Authority]
64	SAT-EXPAK	SATNET and Backroom EXPAK	[Steven_Blumenthal]
65	KRYPTOLAN	Kryptolan	[Paul Liu]
66	RVD	MIT Remote Virtual Disk Protocol	[Michael_Greenwald]
67	IPPC	Internet Pluribus Packet Core	[Steven_Blumenthal]
68		any distributed file system	[Internet_Assigned_Numbers_Authority]
69	SAT-MON	SATNET Monitoring	[Steven_Blumenthal]
70	VISA	VISA Protocol	[Gene_Tsudik]
71	IPCV	Internet Packet Core Utility	[Steven_Blumenthal]
72	CPNX	Computer Protocol Network Executive	[David Mittnacht]
73	CPHB	Computer Protocol Heart Beat	[David Mittnacht]
74	WSN	Wang Span Network	[Victor Dafoulas]
75	PVP	Packet Video Protocol	[Steve_Casner]
76	BR-SAT-MON	Backroom SATNET Monitoring	[Steven_Blumenthal]
77	SUN-ND	SUN ND PROTOCOL-Temporary	[William_Melohn]
78	WB-MON	WIDEBAND Monitoring	[Steven_Blumenthal]
79	WB-EXPAK	WIDEBAND EXPAK	[Steven_Blumenthal]
80	ISO-IP	ISO Internet Protocol	[Marshall_T_Rose]
81	VMTP	VMTP	[Dave_Cheriton]
82	SECURE-VMTP	SECURE-VMTP	[Dave_Cheriton]
83	VINES	VINES	[Brian Horn]
84	TTP	Transaction Transport Protocol	[Jim_Stevens]
84	IPTM	Internet Protocol Traffic Manager	[Jim_Stevens]
85	NSFNET-IGP	NSFNET-IGP	[Hans_Werner_Braun]
86	DGP	Dissimilar Gateway Protocol	[M/A-COM Government Systems, "Dissimilar Gateway Protocol Specification, Draft Version", Contract no. CS901145, November 16, 1987.][Mike_Little]
87	TCF	TCF	[Guillermo_A_Loyola]
88	EIGRP	EIGRP	[RFC7868]
89	OSPFIGP	OSPFIGP	[RFC1583][RFC2328][RFC5340][John_Moy]
90	Sprite-RPC	Sprite RPC Protocol	[Welch, B., "The Sprite Remote Procedure Call System", Technical Report, UCB/Computer Science Dept., 86/302, University of California at Berkeley, June 1986.][Bruce Willins]
91	LARP	Locus Address Resolution Protocol	[Brian Horn]
92	MTP	Multicast Transport Protocol	[Susie_Armstrong]
93	AX.25	AX.25 Frames	[Brian_Kantor]
94	IPIP	IP-within-IP Encapsulation Protocol	[John_Ioannidis]
95	MICP (deprecated)	Mobile Internetworking Control Pro.	[John_Ioannidis]
96	SCC-SP	Semaphore Communications Sec. Pro.	[Howard_Hart]
97	ETHERIP	Ethernet-within-IP Encapsulation	[RFC3378]
98	ENCAP	Encapsulation Header	[RFC1241][Robert_Woodburn]
99		any private encryption scheme	[Internet_Assigned_Numbers_Authority]
100	GMTP	GMTP	[[RXB5]]
101	IFMP	Ipsilon Flow Management Protocol	[Bob_Hinden][November 1995, 1997.]
102	PNNI	PNNI over IP	[Ross_Callon]
103	PIM	Protocol Independent Multicast	[RFC7761][Dino_Farinacci]
104	ARIS	ARIS	[Nancy_Feldman]
105	SCPS	SCPS	[Robert_Durst]
106	QNX	QNX	[Michael_Hunter]
107	A/N	Active Networks	[Bob_Braden]
108	IPComp	IP Payload Compression Protocol	[RFC2393]
109	SNP	Sitara Networks Protocol	[Manickam_R_Sridhar]
110	Compaq-Peer	Compaq Peer Protocol	[Victor_Volpe]
111	IPX-in-IP	IPX in IP	[CJ_Lee]
112	VRRP	Virtual Router Redundancy Protocol	[RFC5798]
113	PGM	PGM Reliable Transport Protocol	[Tony_Speakman]
114		any 0-hop protocol	[Internet_Assigned_Numbers_Authority]
115	L2TP	Layer Two Tunneling Protocol	[RFC3931][Bernard_Aboba]
116	DDX	D-II Data Exchange (DDX)	[John_Worley]
117	IATP	Interactive Agent Transfer Protocol	[John_Murphy]
118	STP	Schedule Transfer Protocol	[Jean_Michel_Pittet]
119	SRP	SpectraLink Radio Protocol	[Mark_Hamilton]
120	UTI	UTI	[Peter_Lothberg]
121	SMP	Simple Message Protocol	[Leif_Ekblad]
122	SM (deprecated)	Simple Multicast Protocol	[Jon_Crowcroft][draft-perlman-simple-multicast]
123	PTP	Performance Transparency Protocol	[Michael_Welzl]
124	ISIS over IPv4		[Tony_Przygienda]
125	FIRE		[Criag_Partridge]
126	CRTP	Combat Radio Transport Protocol	[Robert_Sautter]
127	CRUDP	Combat Radio User Datagram	[Robert_Sautter]
128	SSCOPMCE		[Kurt_Waber]
129	IPLT		[[Hollbach]]
130	SPS	Secure Packet Shield	[Bill_McIntosh]
131	PIPE	Private IP Encapsulation within IP	[Bernhard_Petri]
132	SCTP	Stream Control Transmission Protocol	[Randall_R_Stewart]
133	FC	Fibre Channel	[Murali_Rajagopal][RFC6172]
134	RSVP-E2E-IGNORE		[RFC3175]
135	Mobility Header		[RFC6275]
136	UDPLite		[RFC3828]
137	MPLS-in-IP		[RFC4023]
138	manet	MANET Protocols	[RFC5498]
139	HIP	Host Identity Protocol	[RFC7401]
140	Shim6	Shim6 Protocol	[RFC5533]
141	WESP	Wrapped Encapsulating Security Payload	[RFC5840]
142	ROHC	Robust Header Compression	[RFC5858]
143	Ethernet	Ethernet	[RFC8986]
144-252		Unassigned	[Internet_Assigned_Numbers_Authority]
253		Use for experimentation and testing	[RFC3692]
254		Use for experimentation and testing	[RFC3692]
255	Reserved		[Internet_Assigned_Numbers_Authority]