What’s Behind https://16843009? Decoding IPv4 Integer and Alternate Notations

When you type the seemingly non‑existent URL https://16843009 into a browser, it loads a colorful Cloudflare public DNS page and the address bar changes to https://one.one.one.one/. This happens because the server issues an HTTP redirect.

Running the command curl -i https://16843009 shows a response that includes the line Location: https://one.one.one.one/, indicating that the server tells the client to fetch the resource at the new address.

The integer 16843009 is not random; it is the decimal representation of the IPv4 address 1.1.1.1. An IPv4 address is a 32‑bit unsigned integer, and the conversion follows the formula: a.b.c.d = a×256³ + b×256² + c×256 + d Applying the formula to 1.1.1.1 gives 1×256³ + 1×256² + 1×256 + 1 = 16843009. Hence the two notations are equivalent.

Because they represent the same 32‑bit value, 16843009 and 1.1.1.1 are merely different textual forms of the same IPv4 address.

IPv4 addresses can be expressed in several alternative notations, many of which are legacy but still supported by protocols and tools like curl:

32‑bit integer : 16843009 Hexadecimal : 0x01010101 Octal : 001.001.001.001 Two‑segment dotted decimal : a.b (e.g., 1.65793 where 65793 = 1×256² + 1×256 + 1)

Three‑segment dotted decimal : a.b.c (e.g., 1.1.257)

These notations are rarely used in everyday networking but remain in the specification and source code of networking tools. For example, the curl source contains historical handling of such forms.

Another numeric URL, http://2130706433, resolves to the loopback address 127.0.0.1, demonstrating the same principle.

IPv4 address notations

Although modern applications typically use the familiar dotted‑decimal form, understanding the underlying integer representation helps explain redirects like the one from https://16843009 to https://one.one.one.one/ and clarifies why different textual forms map to the same network endpoint.