Internet Protocol
Embed This Widget
Add the script tag and a data attribute to embed this widget.
Embed via iframe for maximum compatibility.
<iframe src="https://ipfyi.com/iframe/entity//" width="420" height="400" frameborder="0" style="border:0;border-radius:10px;max-width:100%" loading="lazy"></iframe>Paste this URL in WordPress, Medium, or any oEmbed-compatible platform.
https://ipfyi.com/entity//Add a dynamic SVG badge to your README or docs.
[](https://ipfyi.com/entity//)Use the native HTML custom element.
J. Postel · 1981-09
Abstract
RFC 791 specifies Internet Protocol version 4 (IPv4), the fundamental network-layer protocol of the internet. It defines the format of IP datagrams, addressing, fragmentation, reassembly, and the basic routing model used to interconnect networks.
Why This RFC Matters
RFC 791 is one of the foundational documents of the modern internet, establishing the 32-bit IPv4 addressing scheme and the datagram forwarding model that has carried the world's data for over four decades. Its design embraced simplicity at the network layer — IP itself makes no guarantees about delivery or ordering, pushing reliability to higher layers like TCP. The 32-bit address space, which originally seemed vast, eventually drove the development of NAT, CIDR, and ultimately IPv6. Despite its age, IPv4 as defined in RFC 791 remains the dominant network-layer protocol in 2026.