DnsServer/Apps/FilterAaaaApp/README.md

Filter AAAA App

A DNS App for Technitium DNS Server that filters AAAA responses when an A record also exists.

Overview

• Post-processor – modifies responses after core resolution
• AAAA filtering – returns NODATA when A records exist for the same name
• Bypass support – skip local zones, networks, or domains

Integration / extension points

• Implements: IDnsApplication, IDnsPostProcessor
• Runs as a post-processor.

Configuration

dnsApp.config contains these keys:

Property	Type	Default	Description
enableFilterAaaa	boolean	false	Enables filtering.
defaultTtl	number	30	SOA TTL used for NODATA responses.
bypassLocalZones	boolean	false	Do not modify authoritative answers.
bypassNetworks	string[]	[]	Client networks excluded from filtering.
bypassDomains	string[]	[]	Domain names excluded from filtering.
filterDomains	string[]	[]	Domains eligible for filtering; empty means all domains.

Example

{
  "enableFilterAaaa": true,
  "defaultTtl": 30,
  "bypassLocalZones": false,
  "bypassNetworks": [],
  "bypassDomains": ["ipv6.example.com"],
  "filterDomains": []
}

Runtime behavior

1. Only acts on AAAA responses with NoError.
2. Skips signed responses when DNSSEC is in use.
3. Bypasses configured networks/domains and local zones when set.
4. If the same name has an A record, returns NODATA.

Risks / operational notes

• Can break IPv6-only access if misconfigured.
• Adds an extra A lookup per filtered query.
• NODATA responses are cached negatively.