Federation fails when using IPv6 DNS servers

[benhylau]

Federation fails with:

2016-08-10 22:27:45,916 - synapse.http.matrixfederationclient - 183 - WARNING - POST-4- {GET-O-2} Sending request failed to matrix.org: GET matrix://matrix.org/_matrix/federation/v1/query/profile?field=avatar_url&user_id=%40benhylau%3Amatrix.org: InvalidA
ddressError - InvalidAddressError: IPv4 port write() called with IPv6 address

Removing my IPv6 DNS servers in /etc/resolv.conf fix federation:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# nameserver 2001:4860:4860::8844 <-- comment out
# nameserver 2001:4860:4860::8888 <-- comment out
nameserver 8.8.8.8

Seems to be a known issue that has come up in #matrix:matrix.org many times.

[ara4n]

Yup. the official bug for this is https://matrix.org/jira/browse/SYN-254

[ara4n]

...and now fixed on develop by #1696, we believe :)

[ara4n]

...except apparently it's still broken on develop :(

[kyrias]

@glyph Do you know the state of using IPv6 resolvers in twisted, if there's any work going on regarding it? Currently twisted's trunk still doesn't work with them.

[glyph]

@kyrias I'm afraid I don't understand the question. Twisted's trunk only recently added support for them. What do you consider an "IPv6 resolver"?

[kyrias]

@glyph An IPv6 resolver is a resolver queried over IPv6.

[glyph]

@kyrias Oh, so just an IPv6 address for looking up A records, not a resolver that can resolve AAAA records? Huh. In what sense does that not work? Are you talking about something in twisted.names?

[kyrias]

@glyph Yes.

>>> from twisted.names import client
>>> client.getHostByName('google.com')
<Deferred at 0x7f1818a1f290 current result: <twisted.python.failure.Failure twisted.internet.error.InvalidAddressError: >>

[glyph]

@kyrias This is definitely a serious bug in Twisted. It's been filed here - https://twistedmatrix.com/trac/ticket/8877 - unfortunately that's still fairly recent. Sorry about that!

[swift11]

@glyph Weird: it's a bug with "normal" priority in Twisted...

[glyph]

@swift11: Priority is not really used in our bugtracker. You can tell if something is really high priority by whether it gets fixed or not :)