Re: Recommended DNS server for a medium 20-30k users isp

[David Guo via NANOG <nanog () lists nanog org>]

Hi,

We use PowerDNS Recursor together with dnsdist to handle millions of DNS requests per day for more than 100k users. In 
our experience, a small server such as one from the Intel E22xx series with 32 GB of RAM is sufficient for this setup.

Based on my experience, you only need to install dnsdist for load balancing and implement per-IP rate limiting.

Best regards,
David


From: William Herrin via NANOG <nanog () lists nanog org>
Date: Friday, August 8, 2025 at 17:21
To: North American Network Operators Group <nanog () lists nanog org>
Cc: DurgaPrasad - DatasoftComnet <dp () datasoftcomnet com>, William Herrin <bill () herrin us>
Subject: Re: Recommended DNS server for a medium 20-30k users isp

On Thu, Aug 7, 2025 at 5:44 PM DurgaPrasad - DatasoftComnet via NANOG
<nanog () lists nanog org> wrote:
> Do you have any recommendations for recursive DNS servers for a medium sized (20-30k users) ISP.
> We have used powerdns and unbound but sometimes find the caching times a bit on upper side. Any suggestions between 
> these two or anything new?
> Also need points on how much we tune the settings
> pros and cons if any.

Howdy,

For 30k users, a pair of bind9 servers will do just fine without any
special performance tuning. Whether you use bind9 or any other DNS
server software, the key things are that these should be bare metal,
not virtual machines, and they should be dedicated to the DNS task.
VMs or competing workloads introduce latency which will be perceptible
in your DNS performance. You'll observe that the CPU is lightly used
on these machines, and that's the result you want to see.

This is true even if, for some reason, the bulk of your users do not
employ DOH to a public server for the web browser DNS lookups.


On Thu, Aug 7, 2025 at 7:17 PM Smoot Carl-Mitchell via NANOG
<nanog () lists nanog org> wrote:
> DNS clients typically round robin requests between servers.

They do not. DNS resolvers may round-robin requests between
authoritative servers, but clients usually talk to resolvers in the
order configured. It's something to keep in mind if you want to spread
the load between the DNS resolvers. 30k users is not enough for it to
make much difference.

Regards,
Bill Herrin


--
William Herrin
bill () herrin us
https://bill.herrin.us/
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