Optimistic DNS

[lincolnguang]

Prerequisites

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• [-] I am running the latest version
• [-] I checked the documentation and found no answer
• [-] I checked to make sure that this issue has not already been filed

Problem Description

Optimistic DNS can reduce latency caused by DNS resolution when a client reconnects after a record has expired, which idea from apple in page 13.

Proposed Solution

When the local DNS cache expires, Adguard Home can continue answer with the IP in the local cache results with 1 TTL, while a new DNS query is made to update the cache. If client can still connect to the server by using the old results, then that's great and reduces the time waiting for DNS query. And if not, after a short TTL, the new DNS result can be sent to client and reconnect again.

Additional Information

Also, there is another Go project named Clash support this feature, you can check this pr.

[ameshkov]

Makes perfect sense, thanks for filing the feature request!

[lancelot-moon]

This was done in AG for Android...
AdguardTeam/AdguardForAndroid#2539

I'm astonished that it's not provided in AG Home.
Does AG for iOS support Optimistic DNS?

[ameshkov]

I am not so sure DnsLibs (the new implementation that replaced dnsproxy) actually supports optimistic DNS, so I copied this FR there as well: AdguardTeam/DnsLibs#83

[IrineSistiana]

Just in curiosity.

Optimistic DNS can reduce latency caused by DNS resolution when a client reconnects after a record has expired, which idea from apple in page 13.

App developers might know that their servers' IPs will not be changed easily. So it's safe for them to implement Optimistic DNS.

DNS is a system with an eventual consistency model. Is it safe to modify TTL arbitrarily in this way for all clients?

[ameshkov]

Tbh, I doubt it will cause any issues. DNS records TTL does not guarantee an exact precision due to its nature (it's always TTL + latency).