Suggest an editImprove this articleRefine the answer for “What is IPv4?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**IPv4 (Internet Protocol version 4)** is the fourth version of the internet protocol, which provides addressing and routing of packets in TCP/IP networks. **Key point:** the main problem with IPv4 is its limited number of addresses (2^32 = 4,294,967,296), which is why IPv6 is gradually being adopted.Shown above the full answer for quick recall.Answer (EN)Image**IPv4 (Internet Protocol version 4)** is the *fourth version of the internet protocol*, which provides **addressing and routing of packets in TCP/IP networks**. Short phrasing for the interview: > **IPv4 is a network-layer protocol that assigns unique 32-bit IP addresses to devices and delivers packets from a sender to a receiver.** IPv4 is the foundation of the internet and local networks. --- ## Structure of an IPv4 address An IPv4 address is **32 bits**, divided into 4 octets. Example: ``` 192.168.10.25 ``` In binary form: ``` 11000000.10101000.00001010.00011001 ``` Range of each octet: **0-255**. --- ## Tasks of IPv4 1. **Addressing devices** Each device gets a unique IP within a network. 2. **Routing** Packets travel through routers from network to network. 3. **Fragmentation and reassembly of packets** If the MTU is smaller than the packet size, IPv4 can split it into parts. 4. **Data encapsulation** Data from TCP/UDP is packed into an IPv4 header. --- ## Structure of an IPv4 packet (header) Main header fields: - **Version** - protocol version (4) - **Source IP** - the sender's IP - **Destination IP** - the receiver's IP - **TTL** - limits the number of hops - **Protocol** - which protocol is inside (TCP/UDP/ICMP) - **Total Length** - the packet's length Full header: 20-60 bytes. --- ## Types of IPv4 addresses ### 1. Public (external) Used on the internet. Unique worldwide. ### 2. Private (internal) Used in local networks (not routed on the internet). Ranges: - 10.0.0.0/8 - 172.16.0.0/12 - 192.168.0.0/16 ### 3. Loopback 127.0.0.0/8 Usually: **127.0.0.1** - [localhost](http://localhost). ### 4. APIPA (Link-local) 169.254.0.0/16 Assigned automatically when DHCP is unavailable. ### 5. Multicast 224.0.0.0 - 239.255.255.255 ### 6. Broadcast Broadcast address: **x.x.x.255** (in the classic mask) --- ## IPv4 and subnet masks A **subnet mask** is used to split a network into subnets, for example: ``` 255.255.255.0 → /24 ``` It divides the address into: - the **network** part - the **host** part Example of a /24 network: ``` 192.168.1.0/24 Hosts: 192.168.1.1 - 192.168.1.254 Broadcast: 192.168.1.255 ``` --- ## The problem with IPv4 #### 1. Limited number of addresses: 2^32 = 4,294,967,296 That turned out to be too few for the whole world, so the industry started widely using: - NAT - private networks - CIDR - dynamic address allocation #### 2. IPv4 is officially exhausted Regional internet registries (RIPE, ARIN, and others) have handed out their last pools. That is why IPv6 is being developed. --- ## IPv4 vs IPv6 (briefly) | IPv4 | IPv6 | |---|---| | 32 bits | 128 bits | | 4.3 billion addresses | ~3.4×10^38 | | Notation: 192.168.1.1 | Notation: 2001:db8::1 | | Widely used | Gradually being adopted | | NAT is mandatory | Enough addresses, NAT is not needed | --- ## Examples of IPv4 use in reality - a home router hands out addresses like 192.168.x.x - a web server has a public IP like 203.x.x.x - a computer reaches 8.8.8.8 (Google DNS) - a router splits a network into subnets /24, /30, /16 --- ## Ready answer for the interview > **IPv4 is a network-layer protocol that provides addressing and delivers packets in TCP/IP networks.** > **It uses 32-bit IP addresses, written as four numbers separated by dots.** > **IPv4 defines routing, fragmentation, and the packet format.** > **The main problem with IPv4 is its limited number of addresses, which is why IPv6 is gradually being adopted.** --- ## Cheat sheet (5 seconds before the interview) - IPv4 = a 32-bit IP protocol. - Address: 4 octets (0-255). - Format: A.B.C.D, example: 192.168.1.10. - Private ranges: 10/8, 172.16/12, 192.168/16. - Packets are routed by IP. - Problem: too few addresses, so IPv6 was needed.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.