[3xblah]

"So, in practical terms, what's the difference between this CNAME trick and building the same thing in-house to run your own analytics?"

In practical terms, based on what we have seen up to now, few websites will run their own analytics.

Thus, focusing on the third party services is effective against most tracking.

The "CNAME trick" might be viewed as a good thing because it is putting evolutionary pressure on users to utilise DNS to "block" ads instead of using popular graphical web browsers to do the work. These browsers are written by companies or organisations that derive substantial revenue from online advertising.

[icebraining]

> it is putting evolutionary pressure on users to utilise DNS to "block" ads instead of using popular graphical web browsers to do the work

How so? Browser and browser addons are perfectly capable of blocking these subdomains.

[garren]

It's not that browser add-ons aren't capable of blocking them, it's that a) browser extensions generally don't have access to dns resolution, b) even if they did, cname tracker resolution would increase overall latency due to multiple requests to identify trackers /outside/ of normal resolution, c) it's trivial for a host to create a new cname for a tracker, so automating this makes a lot of sense from their perspective in order to avoid blocklists.

Extensions now have to identify which cnames are a front for which trackers, block the new tracker, and somehow manage to stay below the max rules-per-extension that the browser allows (30k for Chrome[0]). See original nextdns.io post for details [1].

[0] https://www.xda-developers.com/google-chrome-manifest-v3-ad-...

[1] https://medium.com/nextdns/cname-cloaking-the-dangerous-disg... ( https://outline.com/Y6PKr3 )

[bscphil]

> it's trivial for a host to create a new cname for a tracker, so automating this makes a lot of sense from their perspective in order to avoid blocklists.

This is the part I'm skeptical of. If your site is HTTPS, and a user forbids mixed content, all your ads have to be served over HTTPS. That means whenever you create a new CNAME, the ad server (not run by you) has to generate a new certificate, or else you have to give them a cert for *.yourdomain.com. Both are pretty big asks. Even if the ad server can automatically generate new certs, they're going to show up in a transparency log and can be automatically added to blocklists based on that.

So I'm not sure it's going to make much of a difference which blocking method people use. All the Easylist (or whoever) folks have to do is add new subdomains to their blocklist - the exact same thing an ad blocking DNS provider is doing.

Edit: the process for obtaining a certificate from Adobe for a new tracking CNAME looks absolutely excruciating, which is good evidence for my point. https://docs.adobe.com/content/help/en/core-services/interfa...

[3xblah]

"... the exact same thing an ad blocking DNS provider is doing."

Just to be clear, I was not advocating using third party DNS.

Using djbdns I can just "block" all non-www subdomains for a domain with a single line in a zone file (if using tinydns) or a single byte file in a directory (if using dnscache) and then add entries in the zone file for any specific subdomains I want to "allow".

It is only an opinion, but I think the ability to wildcard all subdomains makes DNS-based methods of blocking trackers easier to manage and allows it to scale better than having to list every tracker subdomain in a blocklist.

[bscphil]

> Just to be clear, I was not advocating using third party DNS.

Well, you weren't, but the OP is a Show HN by a company offering such a service.

> It is only an opinion, but I think the ability to wildcard all subdomains makes DNS-based methods of blocking trackers easier to manage

I dunno, I think for most people uBlock rules are going to be easier to handle then setting up their own DNS server. Sure, I have my own resolver too (Unbound), but since you need an ad blocker on top of that anyway, I just keep my rules in uBlock. The following is all you need to block all subdomains but allow the bare domain:

  ||example.org^
  @@*/example.org/*

Or to allow www:

  @@www.example.org^

[3xblah]

With uBlock, is it possible to block all subdomains but allow a specific subdomain?

A resolver (e.g., unbound) is only one half of the DNS method I use. The other is an authoritative nameserver (e.g., nsd). For my own purposes, the resolver is optional.