Internet Protocol (IP) Numbers

General info

IANA is a standards organization that controls global IP address allocation, autonomous system number (ASN) allocation, Domain Name System (DNS) root zone managegement, media types (MIME type) and other Internet Protocol related symbols. Currently IANA ia a function of Internet Corporation for Assigned Names and Numbers (ICANN) organization. They delegates allocations of IP address blocks to Regional Internet Registries (RIRs).

General info

In the Internet Protocol version 4 (IPv4), a 8-bit field called "Protocol" identifies the next level protocol.

In Internet Protocol version 6 (IPv6), a field (also 8-bit) is called the "Next Header". Next header can contain Extension Header options that are located between IPv6 header and the transport-layer header in a packet. IPv6 extension headers can have arbitrary length.

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Here are some interesting trivia facts about Internet Protocol (IP) numbers
IP Protocol Numbers

IP numbers depends on the IP version. IPv4 header uses Protocol field and IPv6 header the Next Header field (IPv6 header). They act as markers for the specific protocols contained within data packets and dictate how the subsequent data is structured after the header.

IPv4 vs. IPv6

In both IPv4 and IPv6 headers, there's a designated area reserved for protocol identification, although they are named differently. In IPv4, this area is referred to as the Protocol field, whereas in IPv6, it's known as the Next Header field.


In both IPv4 and IPv6 headers, the sections dedicated to protocol numbers are 8 bits in width, enabling the accommodation of up to 256 distinct protocol numbers.


The Internet Assigned Numbers Authority (IANA) is tasked with the responsibility of overseeing and releasing the roster of IP protocol numbers.

First and Last

The initial protocol number (0x00) is allocated to the IPv6 Hop-by-Hop Option, while the final one (0x3B) is designated for the No Next Header in IPv6.

Common Protocols

Among the widely recognized protocols facilitating internet communication are

  • ICMP (Internet Control Message Protocol) is assigned protocol number 1. It's widely used for diagnostic and control purposes in IP networks, including ping requests and responses.
  • TCP (Transmission Control Protocol) is assigned protocol number 6. It's a core protocol in the Internet protocol suite and is responsible for establishing and maintaining connections between devices.
  • UDP (User Datagram Protocol) is assigned protocol number 17. It's another core protocol in the Internet protocol suite, providing a connectionless communication mechanism suitable for applications where real-time and loss-tolerant data transmission is needed.
  • IP-in-IP (IP encapsulation within IP) is assigned protocol number 4. It's used for tunneling packets within an IP network, often employed in virtual private networks (VPNs) and other network overlay scenarios.
  • GRE (Generic Routing Encapsulation) is assigned protocol number 47. It's a tunneling protocol used to encapsulate a wide variety of network layer protocols inside virtual point-to-point links.
  • ESP (Encapsulating Security Payload) is assigned protocol number 50. It's a protocol within the IPsec suite used for providing confidentiality, integrity, and authenticity for IP datagrams. ESP is commonly employed in Virtual Private Networks (VPNs) and other secure communication scenarios, where data privacy and security are paramount.
    ESP achieves confidentiality through encryption and integrity through the use of cryptographic mechanisms. It encapsulates the payload of IP packets, along with additional security information, to ensure secure transmission over potentially untrusted networks.
    ESP can operate in two modes: transport mode and tunnel mode. In transport mode, only the payload of the IP packet is encrypted and/or authenticated, leaving the original IP header intact. In tunnel mode, the entire original IP packet is encapsulated within a new IP packet, providing end-to-end security between network gateways.
    Overall, ESP plays a crucial role in securing communications over the Internet and other IP-based networks, safeguarding sensitive data from unauthorized access and tampering.
  • OSPF (Open Shortest Path First) is assigned protocol number 89. It's a dynamic routing protocol used in Internet Protocol (IP) networks to distribute routing information within autonomous systems.
  • SCTP (Stream Control Transmission Protocol) is assigned protocol number 132. It's a transport-layer protocol that combines the features of both TCP and UDP, offering reliable, ordered delivery of data along with congestion control and multiplexing.

These are just a few examples of the many protocol numbers and their associated protocols used in IP networking. Each protocol number plays a crucial role in defining how data is transmitted and managed across networks.

Specialized Uses

The well-known port numbers, widely recognized and frequently used on the internet, typically span from 0 to 123. However, for specific and specialized tasks, port numbers can extend far beyond this range to accommodate various niche applications and services.

These numerical identifiers are crucial for the internet's operation, facilitating the accurate routing of data to its intended application or service. Fascinating, isn’t it?