DNS

Web pages today are complex. Your browser will make on average 40¹ DNS queries to find the various parts of an average web page, so implementing a local DNS system is key to keeping things fast.

In general, you can implement either a caching or recursive server with the choice between speed vs privacy.

Types of DNS Servers

A caching server accepts and caches queries, but doesn’t actually do the lookup itself. It forwards the request on to another DNS server and waits for the answer. If you have a lot of clients configured to use it, chances are someone else has already asked for what you want and it can supply the answer quickly from cache.

A recursive server does more than just cache answers. It knows how to connect to the root of the internet and find out itself. If you need to find some.test.com, it will connect to the .com server, ask where test.com is, then connect to test.com and ask it for some.

Comparison

Between the two, the caching server will generally be faster. If you connect to a large DNS service they will almost always have things cached. You will also get geographically relevant results as content providers work with DNS providers to direct you to the closest content cache.

With a recursive server, you do the lookup yourself and no single entity is able to monitor your DNS queries. You also aren’t dependant upon any upstream provider. But you make every lookup ’the long way’, and that can take many hundreds of milliseconds on some cases, a large part of a page load time.

Testing

In an ad hoc test on a live network with about 5,000 residential user devices, about half the queries were cached. The other half were sent to either quad 9 or a local resolver. Quad 9 took about half the time that the local resolver did.

Here are the numbers - with Steve Gibson’s DNS benchmarker against pi-hole forwarding to a local resolver vs pi-hole forwarding to quad 9. Cached results excluded.

    Forwarder     |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  - Uncached Name | 0.015 | 0.045 | 0.214 | 0.046 | 100.0 |
  - DotCom Lookup | 0.015 | 0.019 | 0.034 | 0.005 | 100.0 |
  ---<O-OO---->---+-------+-------+-------+-------+-------+

    Resolver      |  Min  |  Avg  |  Max  |Std.Dev|Reliab%|
  ----------------+-------+-------+-------+-------+-------+
  - Uncached Name | 0.016 | 0.078 | 0.268 | 0.079 | 100.0 |
  - DotCom Lookup | 0.018 | 0.035 | 0.078 | 0.017 | 100.0 |
  ---<O-OO---->---+-------+-------+-------+-------+-------+

Selection

This test is interesting, but not definitive. While the DNS benchmark shows that the uncached average is better, page load perception is different than the sum of DNS queries. A page metric test would be good, but in general, faster is better.

Use a caching server.

One last point: use your ISP’s name server when possible. They will direct you to their local content caching systems for Netflix, Google (YouTube) and Akamai. If you use quad 9 like I did, you may get to a regional content location, but you miss out on things optimized specifically for your geographic location.

They are (probably) capturing all your queries for monetization, and possibly directing you to their own their own advertising server when you mis-key in a domain name. So you’ll need to decide;

Speed vs privacy.