[pptp-server] how to detect GRE filtering?

[Ismandy Ali]

Hi  all,
     Correct me if I am wrong. One way to detect that there is some kind
of filtering on port 1723 is using traceroute to the port 1723. So, how
to detect that there is some kind of filtering  on  protocol 47 for GRE?

any help is greatly appreciated

Kukulkan