Change default DNS resolvers and MTU to 1500

[hawkff]

Summary

• Change fresh-install remote DNS default to Quad9 DoH: https://dns.quad9.net/dns-query
• Change fresh-install direct DNS default to Cloudflare IP DoH: https://1.1.1.1/dns-query
• Change fresh-install global VPN/TUN MTU default from 9000 to 1500

Notes

• This only changes hardcoded defaults in DataStore.kt and global_preferences.xml.
• Existing installs with saved preferences keep their current values.
• No profile import/export behavior is changed.

Validation

• git diff --check
• GitHub CI passed
• CodeRabbit passed
• Greptile passed

[coderabbitai]

📝 Walkthrough

Walkthrough

Default values in DataStore.kt and global_preferences.xml are updated: MTU drops from 9000 to 1500, remoteDns switches from https://dns.google/dns-query to https://dns.quad9.net/dns-query, and directDns switches from https://223.5.5.5/dns-query to https://1.1.1.1/dns-query.

Changes

Default Configuration Value Updates

Layer / File(s)	Summary
MTU and DNS endpoint defaults app/src/main/java/io/nekohasekai/sagernet/database/DataStore.kt, app/src/main/res/xml/global_preferences.xml	mtu default reduced from 9000 to 1500; remoteDns default changed from https://dns.google/dns-query to https://dns.quad9.net/dns-query; directDns default changed from https://223.5.5.5/dns-query to https://1.1.1.1/dns-query. Both the Kotlin DataStore property defaults and the XML preference defaultValue attributes are updated in sync.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐇 Hop, hop, defaults refined!
MTU trimmed, endpoints redesigned,
Quad9 and Cloudflare combined,
The rabbit rewired DNS aligned —
Network preferences optimized! 🌐

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main changes: updating default DNS to Quad9 and MTU to 1500, which are the primary modifications across both modified files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The PR description clearly outlines the three main changes: DNS defaults (Quad9), and MTU reduction (9000→1500), matching the changeset.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@app/src/main/java/io/nekohasekai/sagernet/database/DataStore.kt`:
- Line 129: The default DNS provider in the directDns variable is set to
Cloudflare (1.1.1.1) instead of the intended Quad9 provider (9.9.9.9) for DNSSEC
and malicious-domain blocking. Change the hardcoded default value in the
directDns declaration from "https://1.1.1.1/dns-query" to
"https://9.9.9.9/dns-query" to align with the PR objective.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 634601e7-9d20-4b89-947e-b1ec97adf675

📥 Commits

Reviewing files that changed from the base of the PR and between 03725eb and a3eb787.

📒 Files selected for processing (2)

• app/src/main/java/io/nekohasekai/sagernet/database/DataStore.kt
• app/src/main/res/xml/global_preferences.xml

[coderabbitai]

⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Direct DNS default does not match the stated Quad9 objective.

directDns is set to Cloudflare (1.1.1.1), but the PR objective specifies Quad9 IP-based DoH (9.9.9.9) for DNSSEC + malicious-domain blocking defaults. Please align both code and XML to the intended provider.

Suggested fix

--- a/app/src/main/java/io/nekohasekai/sagernet/database/DataStore.kt
+++ b/app/src/main/java/io/nekohasekai/sagernet/database/DataStore.kt
@@
-    var directDns by configurationStore.string(Key.DIRECT_DNS) { "https://1.1.1.1/dns-query" }
+    var directDns by configurationStore.string(Key.DIRECT_DNS) { "https://9.9.9.9/dns-query" }

--- a/app/src/main/res/xml/global_preferences.xml
+++ b/app/src/main/res/xml/global_preferences.xml
@@
-            app:defaultValue="https://1.1.1.1/dns-query"
+            app:defaultValue="https://9.9.9.9/dns-query"

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@app/src/main/java/io/nekohasekai/sagernet/database/DataStore.kt` at line 129,
The default DNS provider in the directDns variable is set to Cloudflare
(1.1.1.1) instead of the intended Quad9 provider (9.9.9.9) for DNSSEC and
malicious-domain blocking. Change the hardcoded default value in the directDns
declaration from "https://1.1.1.1/dns-query" to "https://9.9.9.9/dns-query" to
align with the PR objective.