Protip: xip.io with dd-wrt
If you're using DD-WRT with DNSmasq and "No DNS rebind" enabled (the default,) add the following to "Additional DNSmasq options" to allow xip.io to work:
rebind-domain-ok=xip.io
Then save and apply settings in DD-WRT. Alternately you can directly edit dnsmasq.conf. Give it a quick test with
dig 127.0.0.1.xip.io
This probably also works for similar services like ngrok.com, nip ...