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markmcn
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DNS Settings DNS server behaviour

Tue Dec 22, 2015 6:46 am

Hi All,
I'm wondering about the behaviour of Router OS when multiple DNS servers are listed under DNS settings.
Are the servers always queried in the order listed?
Or do they round robin?
I want to point our MT's at a DNS server internally which has some internal domains, Currently there isn't a secondary (I'm working on that)
I want to check they will consistently check that server even if an external dns server such as 8.8.8.8 is defined and only use 8.8.8.8 if our internal server is unreachable
I've checked the manual however I don't see this behaviour outlined
Thanks
Mark
 
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ConnectivityEngineer
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Re: DNS Settings DNS server behaviour

Tue Dec 22, 2015 8:13 am

Round Robin.

While I wondered the same thing - I just did a sniff on port 53 traffic - and sure enough - appeared to be round robin.
Glenn Kelley | MCTNA, MTCWE, MTCTCE, RHCE, RHCSS
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markmcn
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Re: DNS Settings DNS server behaviour

Tue Dec 22, 2015 10:34 am

:( This is unfortunate behaviour.
Thank you very much for sharing your findings.
I just used the packet sniffer to capture traffic and pinged a few random hosts. So It sent all the requests to the first server on the list.
So this is interesting that we are seeing different behaviour. I've emailed MT support requesting they advise on the behaviour.
Once I get a reply I will share
 
markmcn
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Re: DNS Settings DNS server behaviour

Tue Dec 22, 2015 11:05 am

http://forum.mikrotik.com/viewtopic.php ... in#p509059
And regarding how servers for queries are chosen that is correct - router will use 1 cache server and only if it starts to not respond will go to next entry and change only if current one is not responding.
Now the next question becomes if the primary server becomes unreachable and the queries start flowing to the secondary, Will they revert to the primary when it become available again without the secondary failing.
 
Sob
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Re: DNS Settings DNS server behaviour

Tue Dec 22, 2015 2:33 pm

Generally the idea of multiple DNS servers is just redundancy. All are equal, all have the same data. If one dies, you can use another, no matter which one. That's all.

If you want to use internal domains known only by your internal server and still be able to access rest of the world in case your internals server is not available, then ask MikroTik to finally implement per-domain forwarding. That would be the proper way.
People who quote full posts should be spanked with ethernet cable. Some exceptions for multi-topic threads may apply.

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