I took a DMOZ[1] dump, extracted all unique domain-name port combinations and checked their IPv6 connectivity. 3 388 012 : 100.000% : total 3 260 296 : 96.230% : IPv4 only 122 560 : 3.620% : bad NS 3 372 : 0.100% : IPv6 working 1 694 : 0.050% : broken or "fake" IPv6 broken: TCP connect failed fake: IPv6 mapped IPv4 addresses (e.g. ::ffff:1.2.3.4) 33.4% of all services that advertised IPv6 failed to deliver or in other words the IPv6 failure rate is ten times the NS failure rate. Seems high, thus a cross check via TLDs' NS: 270 : 100.0% : TLD total (excluding the IDN tests) 268 : 99.3% : IPv4 working 2 : 0.7% : IPv4 broken (HM and KP) 177 : 65.6% : IPv6 working 8 : 3.0% : IPv6 broken 1910 : 100.0% : NS total 1500 : 78.5% : IPv4 only 31 : 1.6% : IPv4 broken 356 : 19.1% : IPv6 working 23 : 1.2% : IPv6 broken IPv6 failure rates of 4.3% (TLD) and 6.1% (NS) is lower than the above 33.4% but are still significantly higher than the IPv4 failure rates of 0.7% (TLD) and 1.6% (NS). TLD root-NSs usually are managed by dedicated infrastructure organisations thus better trouble shooting than the DMOZ listed ones get is expected and suggests the above 33.4% failure rate isn't some kind of sampling artifact. About 4 days later I did a more detailed check of the hosts with broken IPv6: 1624 : hosts total 827 : connection timed out 382 : no route to host 249 : connection refused 95 : network unreachable 54 : SixXS never received a route announcement for that block 43 : broadcast address 30 : * IPv4 in IPv6 22 : IPv6 assignments reclaimed (3ffe::/16) 16 : * no IPv6 (::) 12 : * IPv4 only 10 : * IPv6 working 4 : IPv6 never assigned 4 : local (fe80::/10) 2 : local (::1) 2 : broken NS Issues(cases not marked with a star) do tend to arise but why are fundamental issues like "connection timed out", "no route to host" and "connection refused" so frequent? (testing was done from 2a01:4d0:102::31) Thomas [1] http://www.dmoz.org/help/getdata.html