[pydotorg-www] ipv6 connectivity issues

["Martin v. Löwis"]

> It looks that python.org is not available over IPv6 again: 

Miquel van Smoorenburg of XS4ALL has looked in the issue, and determined
it to be a misconfiguration at the University of Warsaw. UoW was
announcing 2001:6a0:4000::/34 in BGP, even though they own
2001:6a0::/32. XS4ALL has a policy of filtering routes with prefixes
longer than /32 in the 2001::/16 range. Therefore, XS4ALL could not
route to UoW. While this is, strictly speaking, a policy issue at
XS4ALL, this policy is widely accepted in the internet community, and
implemented by more sites than just XS4ALL.

Tomasz Klicki of ICM, University of Warsaw, has since fixed the BGP
announcement, so it seems to be working from our end now (i.e. a
traceroute to spider1.mimuw.edu.pl succeeds).

Michael: if this comes up again, please ask submitters to provide an
IP address of the node from which they have tried to connect (in this
case, hop 1 from Lukasz' report worked as well, but that wasn't
the actual node that he used). The next step is then to do a traceroute
to the machine from dinsdale. If this fails, chances are apparently
high that it fell through the XS4ALL BGP filter.

In the case of the clara.net looking glass, the issue seems more tricky.
When tracing to python.org, they use 2001:504:1::A500:6939:1 as hop 1,
which is a system that appears to be unreachable from many networks.
When connecting elsewhere, they use 2001:A88:0:1::F9, which can be
reached from python.org just fine. I've contacted them.

Regards,
Martin