DNS Name Server (Go)

Simple UDP DNS responder written in Go. It listens on port 53 and answers A (IPv4) queries for a few hard-coded names (for now).

Requirements

• Go 1.25+

Build

make build
# outputs ./ns

Run Port 53 is privileged; run with sudo or grant the binary the capability:

# Option 1: run as root
sudo ./ns

# Option 2: allow binding to low ports, then run normally
sudo setcap 'cap_net_bind_service=+ep' ./ns
./ns

What it does

• Listens on UDP :53
• Supports only IN A questions
• Answers using an in-memory map:
  • example.com. -> 1.2.3.4
  • localhost. -> 5.6.7.8
  • test.local. -> 8.9.1.2
• Returns NXDOMAIN for other names/types

Quick test In another shell after starting the server:

dig @127.0.0.1 example.com A +short
dig @127.0.0.1 localhost A +short
dig @127.0.0.1 test.local A +short

Project layout

• cmd/main.go: starts the UDP server on :53
• internal/dns/handler.go: decodes queries and builds responses
• pkg/utils/utils.go: DNS message pack/unpack helpers