Bug 15126

that's by upstream design (and have been for a very long time).

if an ipv6 address is available, it will always return it, if not it will return an ipv4 one.

you need to completely block out ipv6 init if you want to enforce ipv4

CC: (none) => tmb

(In reply to Thomas Backlund from comment #1)
> that's by upstream design (and have been for a very long time).
> 
> if an ipv6 address is available, it will always return it, if not it will
> return an ipv4 one.

Well guessing that is causing my cups service problems in a default out of the box setup.

> you need to completely block out ipv6 init if you want to enforce ipv4

Any idea what systemd service/trigger I need to disable/mask?

(In reply to Bit Twister from comment #2)
> (In reply to Thomas Backlund from comment #1)
> > that's by upstream design (and have been for a very long time).
> > 
> > if an ipv6 address is available, it will always return it, if not it will
> > return an ipv4 one.
> 
> Well guessing that is causing my cups service problems in a default out of
> the box setup.
> 

Why ? ::1 matches localhost, so it's available... 

> > you need to completely block out ipv6 init if you want to enforce ipv4
> 
> Any idea what systemd service/trigger I need to disable/mask?

Not an systemd thing... it's lower level... you need to block ipv6 module from loading / initializing...

Something like:
echo "alias net-pf-10 off" >> /etc/modprobe.d/disable-ipv6.conf
echo "blacklist ipv6" >>/etc/modprobe.d/disable-ipv6.conf
echo "options ipv6 disable=1" >>/etc/modprobe.d/disable-ipv6.conf

and reboot.


The first line blocks auto-loading
The second line blocks alias loading
The third line ensures it stays disabled even if someone / something force loads the ipv6 module.

(In reply to Thomas Backlund from comment #3)
> (In reply to Bit Twister from comment #2)
> > (In reply to Thomas Backlund from comment #1)
> > > that's by upstream design (and have been for a very long time).
> > > 
> > > if an ipv6 address is available, it will always return it, if not it will
> > > return an ipv4 one.
> > 
> > Well guessing that is causing my cups service problems in a default out of
> > the box setup.
> > 
> 
> Why ? ::1 matches localhost, so it's available... 

It may be but default cups /etc/cups/cupsd.conf Listen directive is
   Listen *:631
which will cause an 
     Jan 24 12:12:58 wb.home.test cupsd[23936]: Unable to open listen socket
     for address [v1.::]:631 - Address family not supported by protocol.
error, which will cause unable to open socket problem when I turn the printer on.

Sounds like a CUPS bug then.

(In reply to David Walser from comment #5)
> Sounds like a CUPS bug then.

I would not think so. If ipv6 is disabled during install, then getent should not be returning something like
$ getent hosts $(hostname)
::1             wb.home.test

instead of
$ dig +short $(hostname)
192.168.0.132

(In reply to Thomas Backlund from comment #3)

> Not an systemd thing... it's lower level... you need to block ipv6 module
> from loading / initializing...

Was still getting applications running ipv6 connections before modprobe commands  gained control or my /etc/sysctl.d/ ipv6 disables.

Workaround is add  ipv6.disable=1 to kernel boot arguments.

Summary: 5b2: getent returning ipv6 value in a ipv4 setup. => 6_s1: getent returning ipv6 value in a ipv4 setup.

(In reply to Bit Twister from comment #6)
> (In reply to David Walser from comment #5)
> > Sounds like a CUPS bug then.
> 
> I would not think so. If ipv6 is disabled during install, then getent should
> not be returning something like

What do you mean by disabled?

CC: (none) => pterjan

(In reply to Pascal Terjan from comment #8)
> > I would not think so. If ipv6 is disabled during install, then getent should
> > not be returning something like
> 
> What do you mean by disabled?

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-desktop root=LABEL=cauldron noiswmd ipv6.disable=1 audit=0 vga=795

$ grep ipv6 /etc/sysctl.d/xx__sysctl.conf
# disable all ipv6
# http://ask.xmodulo.com/disable-ipv6-linux.html
net.ipv6.conf.all.disable_ipv6  =  1
net.ipv6.conf.default.disable_ipv6  =  1
net.ipv6.conf.lo.disable_ipv6  =  1

$ grep -v ^# /etc/modprobe.d/20_xx__custom.conf | sort | uniq

alias net-pf-10 off
blacklist firewire-core
blacklist ipv6
blacklist thunderbolt
options ipv6 disable=1

You say it was disabled during install, did all of this get written by the install?

(In reply to Pascal Terjan from comment #10)

> You say it was disabled during install, did all of this get written
> by the install?

No. I would add ipv6.disable=1 on clean installs in boot setup. 
The rest after install, or would be there on upgrades.