{"id":51,"date":"2026-10-10T09:20:00","date_gmt":"2026-10-10T09:20:00","guid":{"rendered":"https:\/\/www.whatismyipaddressinquire.com\/blog\/?p=51"},"modified":"2026-10-08T03:04:21","modified_gmt":"2026-10-08T03:04:21","slug":"private-ranges-versus-public-ranges","status":"publish","type":"post","link":"https:\/\/www.whatismyipaddressinquire.com\/blog\/private-ranges-versus-public-ranges\/","title":{"rendered":"Private Ranges Versus Public Ranges"},"content":{"rendered":"

TL;DR:<\/strong> Private ranges are hallways reused in millions of networks. Public ranges are the addresses that can be routed between organizations, when they are actually assigned and allowed. A random generator can emit either shape, so you have to read the number before you drop it into a diagram. Private is not a synonym for safe to scan, and public-looking is not a synonym for yours. Sort a few draws with the random IP generator<\/a> until the ranges are boring to recognize.<\/p>\n

The VPN plan that used the office’s hallway<\/h2>\n

A two-person consultancy set up a VPN between a home office and a rented desk. Both ends used 192.168.1.0\/24 because both routers had shipped that way. The tunnel came up and then every other connection got confused, because both sides believed they owned the same hallway. Printers at home appeared as if they were at the desk. The fix was to renumber one side to 192.168.50.0\/24, which is still private and no longer a twin. A random public address would have been the wrong fix. They did not need a public block. They needed two private blocks that did not collide. The generator became useful afterward, when they wrote the setup notes and needed an example of a public-looking client that was clearly not 192.168.1.20.<\/p>\n

The ranges worth recognizing on sight<\/h2>\n

Private IPv4, the blocks anyone may use inside a network and nobody should see routed on the public internet, includes 10.0.0.0\/8, 172.16.0.0\/12, and 192.168.0.0\/16. If a generated address starts with 10, or with 192.168, you are looking at a hallway. 172 is the tricky one: 172.16 through 172.31 are private, and 172.15 or 172.32 are not in that block. People memorize “172 is private” and then mislabel a public address, or the reverse.<\/p>\n

    \n
  • 10.x.x.x:<\/strong> private, very common in offices and clouds.<\/li>\n
  • 192.168.x.x:<\/strong> private, very common in homes.<\/li>\n
  • 172.16.x.x through 172.31.x.x:<\/strong> private. Check the second octet.<\/li>\n
  • Anything else:<\/strong> not these hallways. It might be public, reserved, or documentation. Keep reading.<\/li>\n<\/ul>\n

    What random output is allowed to land on<\/h2>\n

    A generator that picks four numbers with a wide net will sometimes hit a private block and often hit something that looks publicly routable. Neither result tells you the address is unused. Private addresses are heavily used; they are simply used in parallel inside many buildings. A draw of 10.1.2.3 is someone’s server inside someone’s network, and also yours if you assign it inside yours. It is not a unique name on the internet. A draw of a public-looking address might be a unique name on the internet right now. Treating both as “just examples” is fine in a labeled paragraph and careless in a config that dials out.<\/p>\n

    Link-local 169.254.0.0\/16 is a third shape: the address a device gives itself when DHCP fails. It is not a private hallway you plan, and it is not a public address. If a generator emits one, do not use it as the example of a healthy LAN host. Use it as the example of a DHCP failure, or draw again.<\/p>\n

    NAT is why the hallway stays hidden<\/h3>\n

    Home routers translate many private addresses into one public exit. That is why a what-is-my-IP page and a laptop’s adapter page disagree, and why a random private address in a doc must not be described as “what the internet sees.” If your paragraph is about the exit, you want a public-shaped example and a sentence about translation. If your paragraph is about finding a printer, you want 192.168 and a sentence about staying inside the building. The generator will not choose the paragraph for you.<\/p>\n

    A five-minute sorting drill<\/h2>\n

    Generate ten addresses. Mark each private, link-local, or other. For the 172s, look at the second octet before you mark. You should be able to do this without a search box after one sitting. Then take one “other” and decide, separately, whether your document should replace it with a documentation range before publication. Recognition and publication policy are two skills. The consultancy only needed the first skill to stop the VPN collision. The second skill keeps the write-up from naming a stranger.<\/p>\n

    Cloud VPCs reuse the same hallways<\/h3>\n

    A VPC default of 10.0.0.0\/16 and a home lab of 10.0.0.0\/16 will collide the day you connect them, just as the consultancy’s two 192.168.1 networks did. Random-looking private addresses are not unique across companies. When you pick a lab block, write it down and check it against the office and the cloud account before the tunnel exists. The generator can suggest a host inside a block. It cannot see the other networks you already numbered.<\/p>\n

    Name the hallway or do not use it<\/h2>\n

    When a draw starts with 10 or 192.168, call it private in the notes or draw again for a different lesson. When it does not, refuse the shortcut of calling it “fair game.” The consultancy’s overlapping hallways were a private-range problem with a private-range fix. A random public number would have added a routing problem they did not have. Read the range before you fall in love with the specimen.<\/p>\n","protected":false},"excerpt":{"rendered":"

    10, 172.16\u201331, and 192.168 are reusable hallways. A public-looking draw is not automatically yours to contact.<\/p>\n","protected":false},"author":1,"featured_media":38,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"","neve_meta_content_width":0,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":"","footnotes":""},"categories":[4],"tags":[],"class_list":["post-51","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-networking-concepts"],"_links":{"self":[{"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/posts\/51","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/comments?post=51"}],"version-history":[{"count":1,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/posts\/51\/revisions"}],"predecessor-version":[{"id":52,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/posts\/51\/revisions\/52"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/media\/38"}],"wp:attachment":[{"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/media?parent=51"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/categories?post=51"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.whatismyipaddressinquire.com\/blog\/wp-json\/wp\/v2\/tags?post=51"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}