portmasters and traceroutes

Jack McKinney (jackmc@bga.com)
Wed, 5 Jun 1996 09:10:22 -0500 (CDT)

I have seen a weird problem with the portmasters and traceroute.
When we connect a Windows 95 machine to a PM2/3.1.1 with PPP, and then
try to traceroute somewhere, the portmaster never shows up in the
list. It appears to not be responding. I don't have an actual example,
but the tracert from the W95 machine typically looks like:

1 * * *
2 some.computer.com
3 whatever.is.next
...

It does this even with tracert -n (no hostname resolution). IP
addresses show up at each hop except the first: the portmaster.
The portmaster is apprently not responding to the packets as it should
in the first line. My first thought is that the portmaster does not generate
ICMP port unreachable errors when attempting to connect to a non-existant
UDP port. However, I can traceroute form a machine on the LAN side of the
PM to the Windows 95 machine, and the portmaster _does_ show up in the list.
Next thought: it doesn't respond to unreachable UDP ports on the serial
interfaces... not so: If I connect Linux (Slackware, kernel 1.2.13) to the
portmaster and do a traceroute, I _do_ see the portmaster. Next thought:
Windows 95 does not interpret ICMP port unreachable. Not so either: the
other hops do show up.

Has anyone else seen this phenomenon? It sounds like a Windows 95
problem, except that I don't see this problem when I connect a W95 machine
up to a UNIX box over SLIP (so it _could_ be a W95 PPP problem).

--
"You gotta take the time to         Jack McKinney
     smell the daisywheels."        jackmc@bga.com
    -Bob, on Reboot                 Real/Time Communications (451-0046)
                                    Programmer/System Administrator