[Fwd: Re: Making ICMP the default traceroute protocol?]
From: Clark Gaylord (gaylord_at_dirtcheapemail.com)
Date: 01/24/05
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Date: Mon, 24 Jan 2005 13:01:05 -0500 To: freebsd-net@freebsd.org
Marian Durkovic wrote:
> seems that in today's networking environment the original traceroute
>concept utilising high UDP ports no longer works - since those ports
>are now typically blocked by firewalls.
>
> However, when traceroute is performed using ICMP protocol, the results
>are much better.
>
> Therefore, I'd like to propose to patch
>
>src/contrib/traceroute/traceroute.c
>
> so the ICMP protocol is the first one in
I disagree. Firstly, IWFs tend to also block ICMP. Secondly, routers
sometimes queue ICMP differently than UDP (not just in their own
processing, which they almost always do, but also in their forwarding),
giving even more distortion to these data than they naturally possess
otherwise. In particular, if filtering happens, this becomes obvious;
if differential queueing happens, it is difficult to notice that is
likely what is happening as it doesn't break the trace, it just distorts
the data. Finally, knowing that there is some IWF between me and the
destination is usually a good indication of where a performance problem
resides. ;-)
This is most likely to make a difference at the end hop itself, though
of course filtering can happen anywhere along the path.
If you are finding that your destinations tend to need ICMP, I'd
recommend aliasing traceroute to "traceroute -I".
--ckg
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