DNSThingyMagiK

This is my simple, barebones, insecure implementation of a simple DNS server meant for local use. The goal is to support RFC 1035, local records, ad blocking.

For now, it successfully recursively resolves A records.

Features

DNS Message Parsing & Handling

• Can parse and respond to valid DNS queries
• Correctly handles headers (ID, flags, opcode, RCODE)
• Supports question section processing
• Correctly formats answers, authority, and additional sections

Supported Query Types

• A (IPv4 address)
• AAAA (IPv6 address)
• CNAME (Canonical name)
• NS (Nameserver)
• MX (Mail Exchange)
• TXT (Text records)
• PTR (Reverse lookups)
• SOA (Start of Authority)

Query Processing

• Supports recursive queries (if implemented)
• Supports iterative queries (if acting as authoritative server)
• Correctly handles RD (Recursion Desired) flag
• Supports negative responses (NXDOMAIN, NODATA)
• Supports wildcards (*.example.com)

Caching & TTL

• Correctly applies TTL from authoritative responses
• Handles cache expiration and eviction

Error Handling

• Responds correctly to malformed queries
• Returns correct RCODE values (e.g., SERVFAIL, REFUSED, NXDOMAIN) // some
• Handles timeouts and retransmissions

Testing

go test dnsthingymagik/tests

dig @serverip domain.tld

Example:

lovro@LHPw:~$ dig @193.2.231.164 govekar.net

; <<>> DiG 9.18.30-0ubuntu0.24.04.2-Ubuntu <<>> @193.2.231.164 govekar.net
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6752
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;govekar.net.                   IN      A

;; ANSWER SECTION:
govekar.net.            300     IN      A       185.199.109.153
govekar.net.            300     IN      A       185.199.111.153
govekar.net.            300     IN      A       185.199.110.153
govekar.net.            300     IN      A       185.199.108.153

;; Query time: 167 msec
;; SERVER: 193.2.231.164#53(193.2.231.164) (UDP)
;; WHEN: Tue Mar 11 17:40:16 CET 2025
;; MSG SIZE  rcvd: 93

lovro@LHPw:~$

with 8.8.8.8:

lovro@LHPw:~$ dig @8.8.8.8 govekar.net

; <<>> DiG 9.18.30-0ubuntu0.24.04.2-Ubuntu <<>> @8.8.8.8 govekar.net
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19053
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;govekar.net.                   IN      A

;; ANSWER SECTION:
govekar.net.            300     IN      A       185.199.110.153
govekar.net.            300     IN      A       185.199.109.153
govekar.net.            300     IN      A       185.199.111.153
govekar.net.            300     IN      A       185.199.108.153

;; Query time: 51 msec
;; SERVER: 8.8.8.8#53(8.8.8.8) (UDP)
;; WHEN: Tue Mar 11 16:22:12 CET 2025
;; MSG SIZE  rcvd: 104

lovro@LHPw:~$