lazydns

ECS (EDNS Client Subnet) Plugin

ecs prepares EDNS0 Client Subnet (ECS) options and stores them in the request Context metadata for downstream forwarders to include in upstream queries.

Arguments

• forward (bool): copy client-provided EDNS0 options if present.
• send (bool): derive ECS from the client IP (from metadata client_addr) and attach it.
• preset (string): use a preset IP address instead of deriving from client.
• mask4 (int): IPv4 source prefix length (default: 24).
• mask6 (int): IPv6 source prefix length (default: 48).

Examples

Basic forwarding of client-provided options:

plugins:
  - type: ecs
    args:
      forward: true

Derive from client address and send ECS:

plugins:
  - type: ecs
    args:
      send: true
      mask4: 24
      mask6: 56

Use a preset IP for ECS (testing / fixed subnet):

plugins:
  - type: ecs
    args:
      preset: "192.0.2.1"
      mask4: 24

Exec quick-setup

ecs supports an exec-style quick_setup string with comma-separated key=value options, for example:

ecs: forward=true
ecs: send=true,mask4=20,mask6=40
ecs: preset=192.0.2.1

Metadata keys

• edns0_options: Vec<(u16, Vec)> — encoded EDNS0 options produced by this plugin.
• edns0_preserve_existing: bool — whether to preserve existing options when forwarding.

When to use

• Use ecs when upstream selection should be influenced by (or should include) client subnet information, for example when interacting with geo-aware authoritative servers or CDNs.

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