Yes — master.cz has IPv6.

Has both IPv4 (A) and IPv6 (AAAA) addresses.

Measured 2026-11-04 18:37 UTC. We reuse a result for up to a week, so we aren't testing the same site over and over. Check master.cz now

IPv6 readiness

Website, mail and DNS all work over IPv6.

Website over IPv6 master.cz has an AAAA record and answers on it. ✓ 2a01:430:100:2b::5 answers · 443	yes
www over IPv6 www.master.cz has an AAAA record and answers on it. ✓ 2a01:430:100:2b::5 answers · 443	yes
Mail servers (MX) have IPv6 Every mail server has an AAAA record. mail.master.cz ✓ns3.master.cz ✓	yes
Nameservers have IPv6 3 of 3 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up. ns1.master.cz ✓ns2.master.cz ✓ns3.master.cz ✓	yes

First measured 2026-11-04; last confirmed 2026-11-04.

HTTPS over IPv6 · not part of the grade yet
Loads over IPv6 with a valid certificate after 1 redirect: HTTP 200.

https://master.cz/ via 2a01:430:100:2b::5 → 301https://www.master.cz/ via 2a01:430:100:2b::5 → 200

works

Nothing keeping you from an A

Nothing to fix
Show it off: add the badge to your README.
[![IPv6](https://aaaa.bot/badge/master.cz.svg)](https://aaaa.bot/master.cz)

Check again

master.cz Has IPv6

A (IPv4)	80.79.16.235
AAAA (IPv6)	2a01:430:100:2b::5

www.master.cz Has IPv6

A (IPv4)	80.79.16.235
AAAA (IPv6)	2a01:430:100:2b::5

Browsers on dual-stack networks will usually pick IPv6 here (the "Happy Eyeballs" algorithm races both and prefers v6).

Copy the evidence — a citation-ready record of this measurement

IPv6 measurement: master.cz
Measured 2026-11-04 18:37:13 UTC by aaaa.bot (one server on Fly.io, region iad)

A (IPv4):    80.79.16.235
AAAA (IPv6): 2a01:430:100:2b::5
www AAAA:    2a01:430:100:2b::5

Readiness grade A: Website, mail and DNS all work over IPv6.
- Website over IPv6: master.cz has an AAAA record and answers on it.
    2a01:430:100:2b::5: answers (TCP 443)
- www over IPv6: www.master.cz has an AAAA record and answers on it.
    2a01:430:100:2b::5: answers (TCP 443)
- Mail servers (MX) have IPv6: Every mail server has an AAAA record.
- Nameservers have IPv6: 3 of 3 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up.

Reachability = a TCP connection opened on port 443 (or 80).

HTTPS over IPv6 (not graded): Loads over IPv6 with a valid certificate after 1 redirect: HTTP 200.
    https://master.cz/ via 2a01:430:100:2b::5 -> HTTP 301, certificate: valid
    https://www.master.cz/ via 2a01:430:100:2b::5 -> HTTP 200, certificate: valid
DNS answers via DNS-over-HTTPS (Cloudflare). Method: https://aaaa.bot/method
Permanent link: https://aaaa.bot/r/yFEMQKt9pD

Permanent link: aaaa.bot/r/yFEMQKt9pD · How we measure

Checked 2026-11-04 18:37:13 UTC. Full DNS report: dns.pizza/domain/master.cz · Age, certificate and blocklists: how.is/master.cz · JSON: /api/v1/master.cz