IPv6 ConnectivityFrequently Asked Questions
What is an MTU / Path MTU Discovery problem?
IPv6 requires routers to NOT fragment packets — instead, the sender must discover the maximum packet size (MTU) for the path and not exceed it. If ICMPv6 "Packet Too Big" messages are blocked by a firewall, the sender never learns about a smaller MTU, causing large packets to be silently dropped. The result: small web pages load fine, but large pages hang. Check that ICMPv6 Type 2 (Packet Too Big) is permitted through all firewalls in your network path.
Why don't I have an IPv6 address?
IPv6 addresses are provided by your ISP or your router. If you do not have one, your ISP may not yet offer IPv6, your router may not be configured to request one, or your operating system may have IPv6 disabled. Contact your ISP or check your router settings.
What is 6to4?
6to4 is an automatic tunneling mechanism that lets hosts with a public IPv4 address communicate using IPv6 without explicit configuration. It works by embedding the IPv4 address in an IPv6 prefix (2002::/16). The quality of 6to4 varies: it relies on public relay routers that you do not control. Performance may be poor. Native IPv6 from your ISP is strongly preferred.
What is Teredo, and why does it say 'minimum'?
Teredo is a transition mechanism that tunnels IPv6 over UDP/IPv4. 'Teredo minimum' means your Teredo implementation can reach direct IPv6 addresses but cannot resolve IPv6 DNS names (AAAA records). This makes it useless for browsing IPv6 web sites by name. Consider enabling native IPv6 or using a proper tunnel broker.
Why are my tests being blocked by browser plugins?
Ad blockers, script blockers (such as NoScript), and privacy tools often block JSONP requests to external domains. The test works by fetching URLs from several different subdomains; if any of those are blocked, the test cannot run correctly. Try temporarily disabling browser extensions and reloading the page.
IPv6 connections work, but AAAA lookups fail — why?
Some DNS resolvers, operating systems, or browser configurations suppress IPv6 DNS lookups (AAAA records) even when IPv6 connectivity is available. This means your browser will never try to connect to IPv6-only sites by name, even though it could. This is often a resolver or OS configuration issue.
My ISP's DNS server has no IPv6 access — is that a problem?
For most users today, no. However, as more content moves to IPv6-only, a DNS resolver without IPv6 access may be unable to reach authoritative name servers that are IPv6-only, potentially causing resolution failures.
I have IPv6 but my browser avoids it — what does that mean?
When both IPv4 and IPv6 are available and your browser consistently chooses IPv4, it may indicate that your IPv6 connection is flaky or slow. Modern browsers use 'Happy Eyeballs' (RFC 6555/8305), which races both connections and uses whichever wins. If IPv4 always wins, something in your IPv6 path may be slow or unreliable.