[CentOS] IPv6 broken on Linode

[Pete Biggs]

On Thu, 2017-02-16 at 00:37 -0800, Alice Wonder wrote:
> https://forum.linode.com/viewtopic.php?f=19&t=14570&p=72785
> 
> I can not figure out what I need to do.
> 
> Apparently according to linode support, the VM is trying to grab an IPv6 
> address with some privacy stuff enabled by default causing it to not 
> grab the IPv6 address that is assigned to me.

I'm no IPv6 expert (as in I know nothing), but look at the options that
dhclient is using when it's running - there are various v6 specific
options that would affect what's happening. 'man dhclient' is useful
here.

> 
> 
> I know CentOS follows Red Hat so I'm not suggesting this is CentOS's 
> fault, but stuff like this really is why I am a much bigger fan of KISS 
> with simple key=value configuration files that don't seem to exist 
> anymore with Linux networking in the Red Hat world.

Yes they do. Everything concerned with networking is held in flat files
- they may be XML like files or some other structured approach, but
they are there. What you are probably confusing it with is the fact
that most of the config files are written by GUI applications or
maintained by CLI commands rather than editing them by hand. That's all
down to NetworkManager - love it or hate it, but the clue to what it
does is in the name, it manages your network.  If you don't want
something to manage your network, don't use it.

> 
> Anyone know what might be going on? And how to get dhclient to grab the 
> "right" IPv6 address, the same one this VM grabbed no problem for well 
> over a year?
> 

As I said, you need to look at dhclient configuration and command line
options.  If you have NetworkManager running then it will be
controlling what dhclient does so manual editing the files will not
work. Use nmcli to see what's happening and modify the configuration.

P.