Definiendo el campo de Protocolo.

IP usa un número de protocolo en el el encabezado para identificar cual protocolo usar para un datagrama en particular. El ruteador lee el número de protocolo del encabezado, lo compara a las entradas en la tabla de protocolos de transporte, y entonces lo pasa al protocolo apropiado. Por ejemplo, si el número es 6, IP entrega el datagrama a TCP; si el número de protocolo es 17, IP lo entrega a UDP.

Aunque casi siempre se usa TCP o UDP, hay otros protocolos que pueden usar IP, hay aproximadamente 100 protocolos registrados para propósitos especiales. Los números usados por protocolosTCP son asignados y publicados por un grupo llamado Internet Assigned Numbers Authority (IANA). Los números asignados por la IANA son documentados en el RFC1700.

Protocolo	Campo de Protocolo
Transmission Control Protocol (TCP)	6
User Datagram Protocol (UDP)	17
Internet Control Message Protocol (ICMP)	1
IPv6	41
ICMP para IPv6	58
EIGRP	88

 

http://www.iana.org/assignments/protocol-numbers
No.r	Protocol
0	IPv6 Hop-by-Hop Option
1	Internet Control Message
2	Internet Group Management
3	Gateway-to-Gateway
4	IP in IP (encapsulation)
5	Stream
6	Transmission Control
7	CBT
8	Exterior Gateway Protocol
9	any private interior gateway
10	[SGC]
11	Network Voice Protocol
12	PUP
13	ARGUS
14	EMCON
15	Cross Net Debugger
16	Chaos
17	User Datagram
18	Multiplexing
19	DCN Measurement Subsystems
20	Host Monitoring
21	Packet Radio Measurement
22	XEROX NS IDP
23	Trunk-1
24	Trunk-2
25	Leaf-1
26	Leaf-2
27	Reliable Data Protocol
28	Internet Reliable Transaction [RFC938
29	ISO Transport Protocol Class 4 [RFC905
30	Bulk Data Transfer Protocol
31	MFE Network Services Protocol [MFENET
32	[HWB]
33	Sequential Exchange Protocol
34	Third Party Connect Protocol
35	Inter-Domain Policy Routing Protocol [MXS1]
36	XTP
37	Datagram Delivery Protocol
38	IDPR-CMTP IDPR Control Message Transport Proto [MXS1]
39	TP++ Transport Protocol
40	IL Transport Protocol
41	Ipv6
42	Source Demand Routing Protocol
43	[Deering]
44	[Deering]
45	Inter-Domain Routing Protocol [Sue Hares]
46	Reservation Protocol
47	General Routing Encapsulation
48	Mobile Host Routing Protocol[David Johnson]
49	BNA
50	Encap Security Payload for IPv6 [RFC2406]
51	Authentication Header for IPv6
52	Integrated Net Layer Security TUBA [GLENN]
53	IP with Encryption
54	NBMA Address Resolution Protocol [RFC1735]
55	IP Mobility
56	Transport Layer Security Protocol [Oberg]  using Kryptonet key management
57	SKIP
58	[RFC1883]
59	[RFC1883]
60	[RFC1883]
61	[IANA]
62	CFTP
63	[IANA]
64	[SHB]
65	[PXL1]
66	MIT Remote Virtual Disk Protocol
67	Internet Pluribus Packet Core
68	[IANA]
69	SATNET Monitoring
70	VISA Protocol
71	Internet Packet Core Utility
72	Computer Protocol Network Executive [DXM2]
73	Computer Protocol Heart Beat
74	Wang Span Network
75	Packet Video Protocol
76	[SHB]
77	SUN ND PROTOCOL-Temporary
78	WIDEBAND Monitoring
79	WIDEBAND EXPAK
80	ISO Internet Protocol
81	VMTP
82	[DRC3]
83	VINES
84	TTP
85	[HWB]
86	Dissimilar Gateway Protocol
87	TCF
88	EIGRP
89	OSPFIGP
90	[SPRITE
91	Locus Address Resolution Protocol
92	Multicast Transport Protocol
93	AX.25 Frames
94	IP-within-IP Encapsulation Protocol [JI6]
95	Mobile Internetworking Control Pro. [JI6]
96	Semaphore Communications Sec. Pro.
97	Ethernet-within-IP Encapsulation [RFC3378]
98	Encapsulation Header
99	[IANA]
100	GMTP
101	Ipsilon Flow Management Protocol [Hinden]
102	PNNI over IP
103	Protocol Independent Multicast [Farinacci]
104	ARIS
105	SCPS
106	QNX
107	Active Networks
108	IP Payload Compression Protocol [RFC2393]
109	Sitara Networks Protocol
110	[Volpe]
111	[Lee]
112	Virtual Router Redundancy Protocol [RFC3768]
113	PGM Reliable Transport Protocol [Speakman]
114	[IANA]
115	Layer Two Tunneling Protocol
116	D-II Data Exchange (DDX)
117	Interactive Agent Transfer Protocol [Murphy]
118	Schedule Transfer Protocol
119	SpectraLink Radio Protocol
120	UTI
121	Simple Message Protocol
122	SM
123	Performance Transparency Protocol
124	[Przygienda]
125	[Partridge]
126	Combat Radio Transport Protocol
127	Combat Radio User Datagram
128	[Waber]
129	[Hollbach]
130	Secure Packet Shield
131	[Petri]
132	SCTP Stream Control Transmission Protocol [Stewart]
133	Fibre Channel
134	[RFC3175]
135	[RFC-ietf-mobileip-ipv6-24.txt]
136	[RFC-ietf-tsvwg-udp-lite-02.txt]
137	unassigned
252
253	[RFC3692]
254	[RFC3692]
255	[IANA]