[CentOS] CentOS 7, NetworkMangler, and ipv6

[m.roth at 5-cent.us]

James Hogarth wrote:
> On 10 December 2015 at 15:00, <m.roth at 5-cent.us> wrote:
>
>> We've started having a problem with a CentOS 7 server. It looses its
>> IPv6 address, if I understand this issue correctly. We can get in,
>> if we do ssh -4, though.
>>
>> In the logs, I'm seeing this about twice an hour:
>> <warn>  (pid 98466) unhandled DHCP event for interface ens3f0
>>
>> Now, in googling, I get very few hits putting quotes around "unhanded
>> dhcp exception" - in fact, the only one I found that seemed to talk
>> about it was from someone's slackware box, where there was some sort of
>> configuration, perhaps similar to ifcfg-<if>, and they were telling that
>> person to remove it, because it conflicted with what Networkmanager was
>> trying to do, leaving it in a confused state.
>
> Well there's not much to go on here so you're going to have to provide
> more detail ...

Actually, the problem affected one CentOS 6 and one CentOS 7 server.
>
> Does the system lose all ipv6 connectivity (is the fe80:: address
> uncontactable for instance)

Yes. Each lost their IPv6 address.
>
> Does ip addr sh still show the expected global IPv6 address and it's just
> not responding?
>
> Are you using a static ipv6, dhcp ipv6 or SLAAC ipv6 configuration?

DHCP via dibbler.
>
> Does nmcli c sh <conn-name> still have NM thinking there is an address or
> does that show it as gone as well?
<snip>
I passed that along to my manager, and he says it's a *really* useful
thing to know, so thanks, muchly.

Oh, and Gordon - switch isn't ours. These boxen are in the datacenter, and
another division runs that. Probably big Cisco items.

Btw, one of them, at least, had two drops going into it. Removing one
seems to have helped.

        mark