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

[Adam Goryachev]

On 13/3/19 12:19 am, John Horne 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.
>
Maybe also refer them to this: http://shouldiblockicmp.com/

ie, don't block all ICMP.... some is required so that the Internet thing 
works properly...

Regards,
Adam

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Adam Goryachev Website Managers www.websitemanagers.com.au
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