DNS Blocking not Always Effective?

[qwertyuiopas 0]

I have several DNS lists enabled (per device settings), and recently I found that that they're not always effective. By that I means I could still access the supposedly blocked sites irregularly. For example, I could occasionally access https://www3 dot doubleclick dot net (the website will be redirected if the blocking is not effective). Is this is an expected behavior? If so, could this be improvised to have a more strict effectiveness?

Edited ... by qwertyuiopas
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[OpenSourcerer 1363]

Which lists are enabled, and did you check whether the domain is in one of those lists?
You could also try pinpointing which list contains the domain but when enabled does not block the domain.

[qwertyuiopas 0]

I just enabled most ads blocking list, most of them have this domain in the list. Specifically, the most basic "Ads & Trackers Blocklist" have this domain too. I have a personal Scriptable widget setup in my iOS homescreen, so whenever I use the device I notice this issue. Attached is a screenshot when the blocking is not effective (sorry have to redact lots of personal or identifiable information). The red hand icon indicates the blocking is not effective. It's a very simple javascript to test accessibility to the ads site:

async function isAdsBlockActive() {
    try {
        let req = new Request('https://www3.doubleclick.net')
        req.method = "HEAD"
        req.timeoutInterval = 5
        let res = await req.load();
        return false
    } catch (error) {
        return true
    }
}

 

[OpenSourcerer 1363]

Are you sure DNS resolution always goes via AirDNS? Maybe DNS over HTTPS/TLS is enabled, or gets used intermittently (sometimes called Secure DNS or something, not sure with Apple)?
Which VPN client are you using?

[qwertyuiopas 0]

15 hours ago, OpenSourcerer said:

Are you sure DNS resolution always goes via AirDNS? Maybe DNS over HTTPS/TLS is enabled, or gets used intermittently (sometimes called Secure DNS or something, not sure with Apple)?
Which VPN client are you using?

That's a great question. I have no idea, I think it's very unlikely an iOS issue (since VPN on iOS have already exist for quite a long time, if it's a bug I guess it would have been fixed)? I'm using the official Wireguard app. Perhaps AirVPN could comment on this? @Staff

[OpenSourcerer 1363]

1 hour ago, qwertyuiopas said:

I have no idea, I think it's very unlikely an iOS issue (since VPN on iOS have already exist for quite a long time, if it's a bug I guess it would have been fixed)?

It's not a bug if it's a feature. Keep in mind that iOS services for example actively ignore VPN connections, confirmed on iOS 16 and 17. I can certainly imagine them using some Apple DNS server to resolve names for iOS services regardless of DNS settings, and since those widgets are most probably part of an iOS service since an iOS feature is provided, it's possible to connect the dots: DNS resolutions triggered from those widgets may just use the assigned DNS server but with a quick fallback to some Apple DNS server in case it takes "too long".

[qwertyuiopas 0]

That might be the case. Unfortunately I have no way to verify this, at least not via any published documentation on this by Apple. Hopefully someone with deeper knowledge in iOS can verify this.