Suggest an editImprove this articleRefine the answer for “What are private IP addresses?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**Private IP addresses** are special IPv4 address ranges intended for use only within local networks (LAN) and are not routed on the internet. **Key point:** they are reserved by RFC 1918 and require NAT to reach the global network.Shown above the full answer for quick recall.Answer (EN)Image**Private IP addresses** are special IPv4 address ranges intended for use **only within local networks (LAN)** and **not routed on the internet**. Short wording for an interview: > **Private IP addresses are addresses reserved for internal networks, which are not used on the global Internet and require NAT to reach the outside world.** --- ## Why private addresses are needed - So that **any number of devices** inside an office, home, or company can have unique addresses. - To **save public IPv4 addresses**, which are scarce. - To ensure **security**: internal nodes are not visible from the internet. Main idea: > **The internal network uses a private IP, and it reaches the Internet through NAT.** --- ## Ranges of private IPv4 addresses RFC 1918 defines three ranges: ### **1. 10.0.0.0/8** From **10.0.0.0** to **10.255.255.255** Pros: a huge range (16 million hosts). Used in large companies, VPNs, and data centers. --- ### **2. 172.16.0.0/12** From **172.16.0.0** to **172.31.255.255** Used less often, but also common in corporate networks. --- ### **3. 192.168.0.0/16** From **192.168.0.0** to **192.168.255.255** The most common home and office subnets: - 192.168.0.0/24 - 192.168.1.0/24 - 192.168.100.0/24 --- ## Important properties of private addresses #### **1. Not routed on the internet** Routers **filter** private ranges: packets do not pass through the WAN. #### **2. Require NAT to reach the internet** Private IP → NAT/PAT → Public IP This is done by a home router or a corporate firewall. #### **3. Can be reused many times** The same addresses can repeat across millions of different networks. #### **4. Not globally unique** The address 192.168.1.10 can exist at your home, at the office, and at your neighbor's - that is normal. --- ## Usage examples - Home network: - 192.168.0.10: laptop - 192.168.0.1: router - Corporate network: - 10.0.12.15: workstation - 10.1.0.5: file server - ISP / VPN: - 172.16.x.x: different company branches --- ## Why private IP is secure A device with a private IP: - **is not visible from the internet** - **is not directly accessible by IP** - requires port forwarding - is protected by NAT + a firewall This reduces the likelihood of external attacks. --- ## Private vs public IP | Comparison | Private IP | Public IP | |---|---|---| | Internet accessibility | No | Yes | | Routed globally | No | Yes | | Uniqueness | Only within the network | Unique worldwide | | Commonly used | In LANs | On servers, ISP routers | | NAT required | Yes | No | --- ## Common confusion: 192.0.2.x, 198.18.x.x are not private There are other special ranges too: - 192.0.2.0/24: documentation - 198.18.0.0/15: testing But **they are not private**: do not confuse them with RFC 1918.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.