Hi,
I recently enabled IPv6 support on my firewall (Bering-uClibc
3.1.1-beta3) and mostly it's working fine. There is however a problem
with the ntp daemon from package ntpd.lrp (version 4.2.4p3 Rev 1). I
have been using "classic" ntpd in preference to openntpd because I have
had problems with openntpd crashing in the past and I like the better
status reporting that comes with ntpd.
Without IPv6 (i.e. without kernel module ipv6.o loaded) ntpd works fine.
The output in /var/log/daemon.log looks like this:
ntpd[866]: ntpd [email protected] Tue Jan 20 10:48:02 UTC 2009 (1)
ntpd[868]: signal_no_reset: signal 13 had flags 4000000
ntpd[868]: precision = 2.000 usec
ntpd[868]: Listening on interface #0 wildcard, 0.0.0.0#123 Disabled
ntpd[868]: Listening on interface #1 lo, 127.0.0.1#123 Enabled
ntpd[868]: Listening on interface #2 eth0, 192.168.10.66#123 Enabled
ntpd[868]: kernel time sync status 0040
Simply by running "insmod ipv6" and then "svi ntp restart" it changes to
this:
ntpd[888]: ntpd [email protected] Tue Jan 20 10:48:02 UTC 2009 (1)
ntpd[890]: signal_no_reset: signal 13 had flags 4000000
ntpd[890]: precision = 2.000 usec
ntpd[890]: Listening on interface #0 wildcard, 0.0.0.0#123 Disabled
ntpd[890]: unable to bind to wildcard socket address :: - another
process may be running - EXIT
There's a discussion of the problem on the ntp:questions mailing list:
http://149.20.54.235/pipermail/questions/2007-April/013832.html
In summary, on Linux, when a process opens port 123 on the IPv4 wildcard
address "0.0.0.0" this also opens the IPv6 wildcard address "::" so that
when ntpd later tries to specifically open the IPv6 address it fails.
There are some #ifdef entries in the ntp source code which look like
they should address this problem (in particular those checking for
IPV6_V6ONLY) but for some reason they're not working on Bering-uClibc.
I'm running standard ntpd (4.2.4p8) on Fedora 12, with IPv4 and IPv6
addresses, and that works great. I therefore tried building 4.2.4p8 and
also the latest stable version, 4.2.6, for Bering-uClibc but they all
fail in the same way as 4.2.4p3.
I will keep investigating with the aim of getting both IPv4 and IPv6 to
work, but a drastic workaround is to completely disable IPv6 support in
ntpd at compile time. In file source/ntp/buildtool.mk we explicitly pass
"--enable-ipv6" to the "configure" script and changing this to
"--disable-ipv6" makes ntpd work (using only IPv4) even when IPv6
addresses are present. I think that is a better option than having it
fail completely.
Has anybody solved a similar problem with other programs? Since
everything works on Fedora I think this must be due to an issue with 2.4
kernels (as opposed to 2.6), with uClibc or with the Bering-uClibc build
environment.
If nothing better turns up I plan to go ahead and change buildtool.mk to
remove IPv6 support from ntpd.
davidMbrooke
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