IPv4, or Internet Protocol version 4, is a network-layer protocol that moves datagrams from source addresses to destination addresses across interconnected networks. It provides the addressing and forwarding framework, but does not itself guarantee that data arrives, arrives in order, or is retransmitted if lost.
What is IPv4?
IPv4 is the protocol used to address and carry datagrams across networks. Routers examine a datagram’s destination address and forward it toward its destination. As RFC 791 puts it, the Internet Protocol’s purpose is “to move datagrams through an interconnected set of networks.” The specification was published in September 1981 and remains the foundational definition of IPv4, although the RFC Editor notes that parts of it have since been updated.
As an Amazon Associate I earn from qualifying purchases.
An IPv4 address is a 32-bit address, divided into four 8-bit octets. The familiar dotted-decimal form writes each octet as a number separated by periods—for example, 192.0.2.1. The address identifies a source or destination in an IPv4 datagram; it is not the protocol itself.
How does an IPv4 datagram work?
IPv4 carries data in independent datagrams. Each datagram has a header followed by its data. The header identifies the format as IPv4 and contains source and destination addresses, along with fields that help routers and receiving systems handle the datagram.
#1 Best Overall
The header includes a version field, header-length field, service indication, total length, identification, fragmentation flags and offset, Time to Live, protocol identifier, header checksum, source and destination addresses, and optional fields. The version field is four bits; IPv4 uses the value 4. The address fields are four octets apiece.
Header size and datagram length
The Internet Header Length field measures the header in 32-bit words. Its minimum value is five words, or 20 octets; its four-bit maximum value is 15 words, or 60 octets. The 16-bit Total Length field counts the entire datagram, including both header and data, and permits a maximum specified length of 65,535 octets. That field limit does not mean a datagram of that size can travel across every network in practice.
What IPv4 does—and does not—guarantee
IPv4 handles addressing and forwarding, and its specification includes mechanisms for fragmentation and reassembly when networks have different packet-size limits. It does not provide end-to-end reliability, sequencing, or flow control. A datagram may be lost, duplicated, or delivered out of order; IPv4 alone does not correct those outcomes. Other protocols or applications must provide any reliability or ordering they require.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsIPv4 is therefore not a connection-oriented service. Its datagrams are handled independently, rather than as part of a virtual circuit established by IPv4 itself. RFC 791 defines the protocol’s core behavior; RFC 1812 sets out requirements for IPv4 routers and their forwarding role.
Rank #3
Why the distinction matters
When someone says “IPv4,” they mean the Internet Protocol version and its datagram format. An “IPv4 address” is one of the 32-bit addresses used in that format. Keeping the terms separate makes it easier to understand network settings: an address identifies an endpoint at the IP layer, while the protocol defines how datagrams are represented and forwarded.
Quick Recap
Sources
- RFC 791: Internet Protocol, Jon Postel, September 1981.
- RFC 1812: Requirements for IP Version 4 Routers.
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.
