An IP protocol number identifies what comes next in an IP packet: IPv4 carries it in the 8-bit Protocol field, while IPv6 uses the 8-bit Next Header field. For the familiar examples, TCP is 6, UDP is 17, and ICMP is 1. These are not TCP or UDP port numbers; ports identify service endpoints within transport protocols.
What is an IP protocol number?
An IP protocol number is an 8-bit identifier in the IP header that tells a receiver how to interpret the next-level content. The field is named Protocol in IPv4 and Next Header in IPv6. IANA’s Assigned Internet Protocol Numbers registry records the identifiers and their assignments; the IPv6 Next Header column also marks values used for extension headers.
The number is a header value, not a human-readable application name. It indicates the protocol or header type specified by the registry, but by itself it does not establish which application produced a packet or whether traffic is safe.
Common IP protocol numbers
These decimal values and labels appear in the IANA registry. The table is a practical selection, not a complete listing.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →#1 Best Overall
- Used Book in Good Condition
| Decimal value | IANA label | Meaning |
|---|---|---|
| 0 | HOPOPT | IPv6 Hop-by-Hop Options; also marked as an IPv6 extension header. |
| 1 | ICMP | Internet Control Message Protocol. |
| 2 | IGMP | Internet Group Management Protocol. |
| 4 | IPv4 | IPv4 encapsulation. |
| 6 | TCP | Transmission Control Protocol. |
| 17 | UDP | User Datagram Protocol. |
| 41 | IPv6 | IPv6 encapsulation. |
| 47 | GRE | Generic Routing Encapsulation. |
| 50 | ESP | Encapsulating Security Payload; also marked as an IPv6 extension header. |
| 58 | IPv6-ICMP | ICMP for IPv6. |
| 132 | SCTP | Stream Control Transmission Protocol. |
| 253–254 | Reserved for experimentation and testing | Set aside for experimentation and testing. |
| 255 | Reserved | Reserved. |
For any other value, use the live IANA protocol-number table to distinguish assigned values from unassigned or reserved entries. Registry contents can change, so do not treat an old printed list as authoritative for a current packet.
IP protocol numbers versus port numbers
These identifiers answer different questions. The IP protocol number identifies the next-level protocol carried after the IP header. A transport port identifies a service endpoint within a transport protocol such as TCP or UDP.
Rank #2
| Comparison | IP protocol number | Transport port number |
|---|---|---|
| Where it appears | In the IPv4 Protocol field or IPv6 Next Header field. | In the transport protocol header, such as TCP or UDP. |
| What it identifies | The next-level protocol or, for some values in IPv6, an extension header. | A service endpoint associated with a transport protocol. |
| Examples | 6 = TCP; 17 = UDP. | A port value used with a transport protocol; the value alone is not an IP protocol number. |
| Registry | IANA Assigned Internet Protocol Numbers. | IANA Service Name and Transport Protocol Port Number Registry. |
IANA divides the port registry into System Ports (0–1023), User Ports (1024–49151), and Dynamic and/or Private Ports (49152–65535); dynamic ports are not assigned. IANA advises that assigned System and User ports should not be used before registration. These port ranges do not describe IP protocol numbers.
A registered port is not evidence that traffic is legitimate or even that it corresponds to the registered service. IANA’s port registry cautions: “ASSIGNMENT OF A PORT NUMBER DOES NOT IN ANY WAY IMPLY AN ENDORSEMENT OF AN APPLICATION OR PRODUCT, AND THE FACT THAT NETWORK TRAFFIC IS FLOWING TO OR FROM A REGISTERED PORT DOES NOT MEAN THAT IT IS "GOOD" TRAFFIC, NOR THAT IT NECESSARILY CORRESPONDS TO THE ASSIGNED SERVICE.”
Rank #3
For port-name and port-number management procedures, see RFC 6335, which describes the IANA port registry as the authoritative registry for service names and port numbers.
How to look up an IP protocol number
- Open the IANA Protocol Numbers registry.
- Find the decimal value shown in the packet’s IPv4 Protocol or IPv6 Next Header field.
- Read the registry’s name, description, references, and IPv6 extension-header designation where applicable. Check whether the entry is assigned, reserved, or unassigned rather than assuming every possible value names a usable protocol.
The IANA page showed “Last Updated 2026-03-09” when checked. Because assignments and status can change, the live registry is the right source for a present-day lookup.
Rank #4
Why older assigned-number lists may differ
IP protocol assignments are maintained registry data, not a fixed list. The IANA table includes assignments, unassigned ranges, reserved values, experimental/testing values, and references; it also notes that value 84 was assigned to TTP until March 2023. Confirm a current value in IANA’s table rather than relying on an old compilation.
RFC 1700, Assigned Numbers, published in October 1994, is useful historical context, but it is not the live source for current assignments.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsQuick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
