直接看 xip.io 的說明就可以了：「xip.io: wildcard DNS for everyone」。
重點：
10.0.0.1.xip.io resolves to 10.0.0.1
www.10.0.0.1.xip.io resolves to 10.0.0.1
mysite.10.0.0.1.xip.io resolves to 10.0.0.1
foo.bar.10.0.0.1.xip.io resolves to 10.0.0.1
可以拿來測試...