Another IPv6 problem

David Cantrell dcantrell at redhat.com
Mon Oct 23 17:17:55 UTC 2006


Michael H. Warfield wrote:
> Hey all,
> 
> 	I've run into another problem with IPv6 and FC6.  This one is not a
> "show stopper" (which it would be too late for, anyways) and more of an
> extreme annoyance and install problem.
> 
> 	I just went to install FC6 into one of my networks which uses static
> IPv4 addresses and stateless autoconf for IPv6.  Guess what.  Can't do
> it.  If you specify a static IPv4 address in the install, you also have
> to specify a static IPv6 address if you have IPv6 enabled.  That sucks
> out loud.  IPv6 and IPv4 configurations are independent.

In stage 1, yes.  If your network settings need to be configured that 
way post-install, you can set it up that way with the stage2 network 
configuration screen.

> 	What's worse, I now realize, is that if you are using dhcp for IPv4,
> it's also attempting to use dhcp6 for IPv6!  Gag!  That can result in
> terrible slowdowns for network startup in IPv6 environments which are
> only using stateless autoconf, whether you are using dhcp for IPv4 or
> static IPv4 addresses.  If people are wondering why their FC6 installs
> take forever to configure their network interfaces - surprise, you've
> got IPv6 enabled and are using dhcp for IPv4 and don't have an IPv6
> dhcp6 server.  Let the bitching begin.

IPv4 and IPv6 DHCP are enabled by default for network installs.  Pass 
'noipv6' or uncheck the IPv6 box in stage1 if you want to skip bringing 
up IPv6 for installation.  Theses settings carry over to stage2, but you 
can change them before it writes out the config files on the host system.

> 	Bascally, someone was thinking in terms of IPv4 think when they
> designed the installer and took no allowance for IPv6 autoconf (which
> should be the most common method) and assumed that if you had IPv4 dhcp
> you would have IPv6 dhcp, which is patently not a valid assumption at
> all.  There are certainly reasons and advantages to having a dhcp6
> server, but I'm just betting that very few installations are going to.

Yes, I was thinking that.  IPv6 autoconf will work its way in to rawhide 
post-FC6.  Your help and input testing rawhide after FC6 would be really 
useful.

> 	The choices for IPv4 and IPv6 are orthogonal and different.
> 
> 	IPv4:	dhcp  / static / disabled
> 	IPv6:	dhcp6 / static / autoconf
> 
> 	If IPv6 is loaded, there appears to be no practical way to "disable"
> IPv6 on an interface and the default is for "stateless autoconf" if IPv6
> forwarding is disabled (/etc/sysctl.conf).
> 
> 	Workaround is to disable IPv6 on that interface at install.  It really
> doesn't disable IPv6 at all, it still configures and will then autoconf,
> if you have IPv6 forwarding disabled).  So, "disabling" IPv6 has exactly
> the opposite effect and results in it being enabled and autoconf'ed
> properly.  Some of life's little ironies.

Please describe this RFE in Bugzilla.  I've been talking to someone else 
about the IPv4/IPv6 options in the installer.  What we have right now is 
definitely not complete and/or correct in all places.  There are many 
things that need to be completed here, but it's difficult to work what 
appears to be a simple change in to the installer.  I'd like to know all 
possible configuration paths and then do the UIs.

-- 
David Cantrell
Red Hat / Westford, MA




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