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

John Horne john.horne at plymouth.ac.uk
Tue Mar 12 14:19:51 CET 2019

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.

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 Horne | Senior Operations Analyst | Technology and Information Services
University of Plymouth | Drake Circus | Plymouth | Devon | PL4 8AA | UK

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