[Nagiosplug-help] check_udp suitable to mimic traceroute?

[Ralph.Grothe at itdz-berlin.de]

Hello Nagios Users,

mapping of our network topology close enough to reality gives me
some headache
because many of the gateways along the routes that my nagios
checks pass
there are, what I like to call "black hole gateways", that don't
reply to
ICMP packets.

Though I suspect that all of them are so called "manageable" and
thus should
support at least SNMPv1 (or even better) I am not given queryable
OIDs, nor
the community phrase (if GETs were enabled at all) from the
devices' admins
(most of whom I even don't know).

Thus, a decent check_snmp would be futile and the usual
check_icmp would fail.
However, I found that at least a few of those devices appear in
the hop stack of
a traceroute output to many of my monitored hosts.

This indicates to me that in the end not all of the gateways are
that 
"black holeish", but release some light rays in form of ICMP
response packets,
like "TTL expired", which I guess traceroute's functionality
relies on.

I am not into packet mangling apart from occassional snoop or
tcpdump
packet sniffs when trouble calls for it.
Therefore, I would like to resort to available plug-ins instead
of having to
write my own ones at that level if possible.
The best I think I could achieve anyway, would be to write a Perl
plug-in that
builds on Net::Pcap or similar if I referred to the appropriate
RFCs.

So to avoid the hassle could one use check_udp, or any other of
the vanilla plug-ins,
to this end?

All I know is that such a UDP datagram would probably require the
TTL set to 1
to have the checked gateway decrement it by one and send an ICMP
expiration
notification packet back to the sender, much like traceroute.

But how would one combine UDP query and ICMP response with
available plug-ins?

Regards

Ralph