DNS Resolution very slow

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Posts: 17
Joined: Mon Jun 06, 2016 8:31 am

DNS Resolution very slow

Unread post by Jackal-75 » Thu Sep 15, 2016 12:25 am

Hello guys,

since i put my synology nas (with DNS server installed) like primary DNS resolver for my DHCP scope, all client got very long DNS resolutions times, it forward to the router which forward directly to google DNS.
I've skipped it by setting the NAS like secondary and problem disappear query directly at router, anyone know this problem and how solve it?

All DHCP client are connected by wifi or cable to the router, same for the NAS, mine is a little network with maximun 10 or 12 devices connected, NAS is located at 50Mt cable lenght far from router and there is a switch before it, i am in fear for broadcast domain problem but usually these problem ar in the big network and switches should eliminate collisions' problems.


Posts: 16
Joined: Fri Nov 27, 2015 2:58 pm

Re: DNS Resolution very slow

Unread post by kolossi » Sat Feb 17, 2018 1:34 pm

I know this is an old post, but just to say I found the default cache size in Synology DNS Server of 10MB seems to be completely inadequate.

Go to DNS Server from DSM desktop, then Settings, and set "Maximum Cache Size" to 50MB or larger if you can afford it from your NAS's current memory use.

With 10MB set, I was consistently getting 400-500ms for dns lookups from the browser, even for sites recently looked up. I cleared the _browser_ cache between each test, but Synology dns server clearly wasn't caching its lookup.

Changing the cache size to 50MB got it to more like 200ms which was on a par with setting the DNS server on the PC direct to google's
2xDS415+ (2x4TB+2x2TB/1x4TB, WD Red, Raid1/btrfs, Mem:8GB), 2TB c2 backup
Mailplus Server, Chat, Moments, Audio station, Note station, Mediawiki, Hyperbackup,
Dns server, Dhcp, Universal search - and lots of files


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