# Connectivity test and score

Canonical page: https://test-ipv6.run/

The test starts when the page loads and runs in the visitor's browser. Each test fetches a small object from a host with a specific DNS setup and records success, failure, timeout and latency.

## The tests
1. **IPv4 DNS record**: a host with only an A record. Expected to succeed on almost every network.
2. **IPv6 DNS record**: a host with only an AAAA record. Fails on networks without IPv6; a quick failure is acceptable, a long timeout is not.
3. **Dual-stack DNS record**: a host with both A and AAAA records. The most important test: if it fails or times out, many websites that publish IPv6 will be slow or unreachable.
4. **IPv6 large packet (MTU/PMTUD)**: compares a small and a larger object over IPv6. Failure points to MTU or Path MTU Discovery problems, often caused by tunnels, PPPoE or firewalls dropping ICMPv6.
5. **Dual-stack large object**: dual-stack performance with a larger payload.
6. **Default protocol**: which protocol the browser picks when a site offers both. Runs only when the IPv4 and IPv6 tests both pass.
7. **IPv6-only DNS server**: whether the visitor's DNS resolver can reach authoritative nameservers that only have IPv6 addresses.

## Score and readiness
The page shows an IPv6 score and an IPv4 score from 0 to 10, and a readiness level:
- **Full IPv6 Support** (10): IPv4, IPv6 and dual-stack all work with good performance.
- **IPv6 Available** (8–9): IPv6 works, with minor issues listed.
- **Partial dual-stack**: IPv4 and IPv6 work but the dual-stack test did not pass cleanly.
- **Broken IPv6** (0): IPv6 is configured but does not work, so dual-stack sites may hang for a long time before falling back. Fix IPv6 or disable it until the ISP offers working native IPv6.
- **IPv4 only** (0): no IPv6 connectivity. Common; most sites still work over IPv4.
- **IPv6 only**: no IPv4 connectivity, for example on some mobile networks with NAT64.

Points are taken off for MTU problems, slow IPv6 or IPv4 responses, an unreachable IPv6-only nameserver, and a browser that avoids IPv6 even when it works. Results that are still running are shown as pending rather than failed.

## Common causes of a low score
- The ISP or router has not enabled IPv6, or the router hands out IPv6 addresses without a working route.
- A VPN or proxy that tunnels only IPv4, or blocks IPv6.
- Firewalls dropping ICMPv6 "Packet Too Big" messages (MTU/PMTUD failures).
- A DNS resolver without IPv6 transport.

Related: [Domain IPv6 checker](https://test-ipv6.run/domain-checker.md), [Readiness map](https://test-ipv6.run/readiness-map.md), [Overview](https://test-ipv6.run/index.md).