> > No, that wasn't the reason.   Traceroute uses udp because udp is "real"
> > traffic - that is, routers are going to be routing udp packets just the
> > same way they process any other packets between the source and destination.
> > ICMP is occasionally treated somewhat specially.   If you want honest
> > traceroute reports it is better to get them from packets as close to being
> > real traffic as possible.
> 
> I really don't buy that.
> 
> I mean I _really_ don't buy that.  I have never heard anyone use that as
> the reason before and I have heard a lot of people who should know state
> that it is because of the reason I gave.
> 
> The number of places where ICMP will be routed differently is very small.

Not "routed differently". "Treated somewhat specially" is a reasonable
description of how for instance Cisco routers process ICMP messages (that
must be handled by the router itself) at lower priority than other traffic.
ICMP messages passing *through* the router is treated like any other
traffic.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no