[pptp-server] how to detect GRE filtering?

[Neale Banks]

On Tue, 29 May 2001, Ismandy Ali wrote:

>      Correct me if I am wrong.

I'll try ;-)

> One way to detect that there is some kind
> of filtering on port 1723 is using traceroute to the port 1723.

Not sure how you would achieve this with traditional traceroute, which
typically uses UDP (unix) or Ping (MS) to probe the path.

You could however use hping for this.  See:

	http://www.kyuzz.org/antirez/hping.html

> So, how
> to detect that there is some kind of filtering  on  protocol 47 for GRE?

Maybe hping can do this now too (I don't know).  There are patches for
unix traceroute to use GRE packets.

Some of us have posted pointers to patched-traceroute packages (.rpm,
.deb) here.

The original patch is at:

ftp://ftp.rubyriver.com/pub/jhardin/masquerade/ip_masq_vpn.html

HTH,
Neale.