TL;DR

*.10.20.30.40.nip.io resolves to 10.20.30.40. *.10.20.30.40.sslip.io too.

When experimenting (e.g. with Dokku) it’s useful to be able and set up some resolvable DNS name that maps onto a specific address, without the need to get our own domain.

Enter nip.io, sslip.io and - if all that you need back is just 127.0.0.1, everything that still works in this gist.

There are a few variations that can be useful, let’s see some examples assuming that our target IP address is 10.20.30.40.

• For something really intuitive and quick, just put your IPv4 address and follow it with .nip.io:

10.20.30.40.nip.io   # --> 10.20.30.40

• everything that comes before it is valid too, i.e. there are wildcards all down the rabbit hole:

www.10.20.30.40.nip.io        # --> 10.20.30.40, a regular service
whatever.10.20.30.40.nip.io   # --> 10.20.30.40, first-level wildcard
app1.dokku.10.20.30.40.nip.io # --> 10.20.30.40, second-level wildcard

• if all these dots are likely to annoy your application, it’s possible to substitute them with dashes. It’s still quick, although possibly a little less intuitive:

10-20-30-40.nip.io            # --> 10.20.30.40, look, dashes!
whatever.10-20-30-40.nip.io   # --> 10.20.30.40, *dot* after whatever
whatever-10-20-30-40.nip.io   # --> 10.20.30.40, *dash* after whatever

• Too long to type? Hexadecimal representation to the rescue! The hexadecimal counterpart of 10.20.30.40 is 0a141e28, so:

0a141e28.nip.io            # --> 10.20.30.40, look, hexadecimal!
whatever.0a141e28.nip.io   # --> 10.20.30.40, *dot* after whatever
whatever-0a141e28.nip.io   # --> 10.20.30.40, *dash* after whatever

Want to transform your dotted representation into hex? No problem:

$ perl -e 'printf "%02x%02x%02x%02x\n", split /\./, shift' 10.20.30.40
0a141e28

• Need support for IPv6? Shift to sslip.io, two additional chars to type but you’re asking for 6 instead of 4, so you have to give 2 more! In this case, you can only go with dashes:

--1.sslip.io                  # --> ::1
2a01-4f8-c17-b8f--2.sslip.io  # --> 2a01:4f8:c17:b8f::2

• In a local development environment, you can also leverage many more services that support wildcards and just answer with 127.0.0.1:

here.fbi.com
what.ever.localtest.me
hey.mama.lacolhost.com

So now, future me… you will not forget!

To everyone else: stay safe folks!