CentOS - Jul 2017 - CentOS 7, NM, and IPv6

Hi, folks,

   I and the other admin here have just been assigned a mission... here's
what's happening: only very recently - the last week? our CentOS 7
boxes, or at least some of them, will lose their IPv6 addresses, and
not get it back.

   1. We're running dibbler on the same box that serves DHCP.
   2. It's been working for many months.
   3. The lease file remains in place.
   4. It appears to try, several times, and then give up - as our
       manager puts it, "I to renew the lease", "Here it
is","Nope,
       don't like that, try again", and eventually, after 4 or 5 or
       so tries, gives up.

   One very show-stopping result of this is that NFS starts timing out.

   So: has anyone else seen this behaviour recently, and does anyone have
some idea of what might be going on here?

       mark

On 07/12/2017 07:13 AM, m.roth at 5-cent.us wrote:
>     4. It appears to try, several times, and then give up - as our
>         manager puts it, "I to renew the lease", "Here it
is","Nope,
>         don't like that, try again", and eventually, after 4 or 5
or
>         so tries, gives up.

NM tends to log fairly verbose information.  It sounds like you've 
looked at the network traffic.  Have you looked at the logs on the 
affected systems?

On 07/12/17 12:09, Gordon Messmer wrote:
> On 07/12/2017 07:13 AM, m.roth at 5-cent.us wrote:
>>     4. It appears to try, several times, and then give up - as our
>>         manager puts it, "I to renew the lease", "Here
it is","Nope,
>>         don't like that, try again", and eventually, after 4
or 5 or
>>         so tries, gives up.
> 
> 
> NM tends to log fairly verbose information.  It sounds like you've
looked at
> the network traffic.  Have you looked at the logs on the affected systems?
> 
Sorry, never got around to answering earlier, and we were all still looking.

First, a correction: the same thing is happening on C6 servers.

Next, there is *nothing*, not in dmesg*, not in /var/log/messages, to indicate 
when it failed, nor any failure message. No indication why the daemon didn't
restart it.

* Ok, I've got one good thing to say about C7: dmesg -H. Love it.

       mark

On 12/07/17 16:13, m.roth at 5-cent.us wrote:
> Hi, folks,
> 
>    I and the other admin here have just been assigned a mission...
here's
> what's happening: only very recently - the last week? our CentOS 7
> boxes, or at least some of them, will lose their IPv6 addresses, and
> not get it back.
> 
>    1. We're running dibbler on the same box that serves DHCP.
>    2. It's been working for many months.
>    3. The lease file remains in place.
>    4. It appears to try, several times, and then give up - as our
>        manager puts it, "I to renew the lease", "Here it
is","Nope,
>        don't like that, try again", and eventually, after 4 or 5
or
>        so tries, gives up.
> 
>    One very show-stopping result of this is that NFS starts timing out.
> 
>    So: has anyone else seen this behaviour recently, and does anyone have
> some idea of what might be going on here?
> 
>        mark
> 
I admit that I'm a big fan of either static ipv6 or then just
slaac/radvd for automatic addr assignement.

But I was faced once with that dibbler problem, but don't know how the
dibbler daemon was configured (nor how it's configured at your side either).

From the discussion I had with the DC support people (online.net,
hosting company in France) they wanted me to use a dibbler client, which
I didn't want to, and they wanted me to specific the DUID that dibbler
at the server side would use to recognize the dhclient request.

So here is what I did (worth knowing that ipv6.method is set to 'ignore'
from a NM PoV) :

create the /etc/dhcp/dhclient.d/dhclient6.conf :
interface "eth0" {
   send dhcp6.client-id my:long:duid:id:that:dibbler:wants:bla:etc ;
}

And then "plumb" it in a NetworkManager dispatcher.d script (I
*really*
like dispatcher.d script as you can take action when some interface are
up/down, etc ....):

/etc/NetworkManager/dispatcher.d/99-ipv6-online.sh :

#!/bin/bash
IF=$1
STATUS=$2

if [[ "$IF" = "eth0" && "$STATUS" =
"up" ]] ; then
  logger "IF $IF status changed to $STATUS"
  sleep 10
  logger launching ipv6 client for $IF
  /usr/sbin/dhclient -cf /etc/dhcp/dhclient.d/dhclient6.conf -6 -P -v
eth0 -nw

fi

YMMV but I hope that it will help you

PS : never looked at this again but maybe NM has now a way to specify
that directly ?


-- 
Fabian Arrotin
The CentOS Project | http://www.centos.org
gpg key: 56BEC54E | twitter: @arrfab

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