[Xymon] What does the 'dns' test do?

SebA spah at syntec.co.uk
Tue Mar 12 14:57:00 CET 2019

I don't really understand why you would be negating the dns test on the
server, rather than just removing it altogether.  You will be slowing down
xymonnet if you have tests that are getting blocked by firewalls /
iptables.  If you're interested in a test that checks iptables is running,
I made a simple extension script I might be able to share.

Kind regards,


On Tue, 12 Mar 2019 at 13:20, John Horne <john.horne at plymouth.ac.uk> wrote:

> On Sun, 2019-03-10 at 21:17 +0000, John Horne wrote:
> > Hi,
> >
> > Using the 4.3.28 Terabithia RPMs, can someone tell me what the 'dns' test
> > actually does?
> >
> > We actually negate the test ('!dns'), and run a client-side dns test
> ('dnsr')
> > to check that resolution is working. As far as I remember the standard
> 'dns'
> > test checks that the client DNS service can resolve something. This will
> > always fail in our case as the client DNS service is always restricted to
> > just the local host. (No querying allowed from an external server.)
> >
> > I'm trying to work out why most of our servers are taking less than a
> second
> > - giving a 'Server unavailable' reply, but others are taking around 20
> > seconds for a 'Timeout' reply. I know why the timeout is 20 seconds, I'm
> just
> > wondering why it's not giving a 'Server unavailable' reply.
> >
> Hi,
> Thanks for the replies about this.
> It seems the network infrastructure in which our monitoring server sits is
> blocking ICMP from some networks. Clients in those networks are correctly
> sending back an ICMP reject via its local firewall, but these are blocked.
> So
> the Xymon server times out the connection instead. I've asked if ICMP
> rejects
> can be allowed through.
> John.
> --
> John Horne | Senior Operations Analyst | Technology and Information
> Services
> University of Plymouth | Drake Circus | Plymouth | Devon | PL4 8AA | UK
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