[nzlug] Ping/Traceroute issue.. Nagios involved.. VMWare involved..

[Nick 'Zaf' Clifford]

Michael Hutchinson wrote:
> <snip> 
>
> We have noticed an anomaly recently, to do with the ability of Bob to
> ping certain monitored sites. Occasionally, PING will start failing for
> one site and continue to fail for some time. If we take any other
> computer on the same subnet, and get it to ping the site, it works. Bob,
> however, cannot. Bob still monitors all other sites just fine. We have
> used other PC's right next to Bob (same network, same external IP
> address) both with windows and linux OS's but Bob is the only one with
> the issue. 
>   
<snip>


When you say PINGs are failing, are you talking about just using Nagios
(eg it pipes up with PING failures), or are you also talking the actual
command, ping.
Eg do you log into the box, and type: ping <target>, and get any response?
If the ping command works, then its almost definately a Nagios fault,
and needs to be reported on that mailing list.

If the ping command doesn't work, then we get into the fun stuff.

Can the nagios box ping any other host on the target network, or any
other network?

Someone mentioned wireshark. This is a nice gui tool, but tcpdump is
perfectly suitable to doing this type of analysis, and has minimal
dependancies.

Run tcpdump icmp > ping.log on both machines (eg the nagios machine and
the machine that is failing), and compare. You should see something like:
nagios->target icmp ping request
target->nagion icmp ping reply

If both logs are showing that, then great, everything is, in theory,
working (if its not then you've got even more oddities!)

I suspect you'll find that either the target isn't getting the pings, or
the replies aren't reaching nagios.

I'd also look closely at any cheapish ADSL routers on either end. I've
found some that block both outgoing and incoming ping requests and
replies (<sarcasm>because, maybe sending a ping to someone, and getting
a response, could be dangerous!</sarcasm>).
I've also found some cheap ADSL routers that fail intermittently.

Hope that helps,
Nick