Hi,

Some thoughts...

I think DHCPv6 uses ports 546 / 547 for client and server, so perhaps have a sniff with tcpdump for activity there - is there evidence of message exchanges?

Unless there's some other way you configure default gateway and on-link prefixes, you'll need Router Advertisements to be running and processed by the client, but if using DHCPv6 for address configuration that shouldn't prevent such configuration.

What is configured server-side - are specific IPv6 addresses allocated by DUID?  As others have said, perhaps the DUID changed during the OS reinstall / upgrade.

Maybe also check the client's ip6tables firewall is allowing DHCPv6 responses through on port 546.

Tim 

> On 18 Sep 2018, at 10:49, Doidge, Matt <[log in to unmask]> wrote:
> 
> Thanks for the reply Dave,
> I'm fumbling around but I don't think our C7 nodes are getting their addresses at all. Their is no dhcp6 lease file, and if you look at the ifconfig output the v6 "bits" are missing the line with the "proper" v6 address in it. (That's a lot of "", which kind of shows my level of expertise on the matter):
> 
>       inet6 2001:630:80:2fd:f4d9:6be9:5401:38cc  prefixlen 64  scopeid 0x0<global>
>        inet6 fe80::130:d584:5f51:783  prefixlen 64  scopeid 0x20<link>
> 
> And that's the lot.
> 
> I'm not actually on the v6 working group list, so thank you very much for forwarding my issues to them
> 
> Cheers!
> Matt
> 
> ________________________________________
> From: Testbed Support for GridPP member institutes <[log in to unmask]> on behalf of David Kelsey - UKRI STFC <[log in to unmask]>
> Sent: 18 September 2018 10:07:03
> To: [log in to unmask]
> Subject: Re: CentOS7 Nodes not getting v6 addresses
> 
> Hi Matt,
> 
> Are the CentOS 7 machines successfully getting IPv6 addresses but then not binding to them?  Or is the problem relating to getting an address in the first place?
> 
> If the latter (and thinking completely theoretically with no actual experience ;=))  is the CentOS 7 creating a DUID correctly?  DUID is the DHCPv6 unique identifier used in the exchange with the DHCPv6 server (like DHCPv4 uses MAC address).  Or perhaps the DUID has changed in moving from 6 to 7?
> 
> I have asked my colleagues on the IPv6 working group for their thoughts.  This sort of trouble-shooting guidance is something we should document in our knowledgebase.
> 
> Good luck,
> Dave
> 
> ------------------------------------------------
> Dr David Kelsey
> Particle Physics Department
> STFC Rutherford Appleton Laboratory
> Chilton, DIDCOT, OX11 0QX, UK
> 
> e-mail: [log in to unmask]<mailto:[log in to unmask]>
> Tel: [+44](0)1235 445746 (direct)
> ------------------------------------------------
> 
> 
> 
> From: TB-SUPPORT <[log in to unmask]> on behalf of "Doidge, Matt" <[log in to unmask]>
> Reply-To: TB-SUPPORT <[log in to unmask]>
> Date: Tuesday, 18 September 2018 at 02:07
> To: TB-SUPPORT <[log in to unmask]>
> Subject: CentOS7 Nodes not getting v6 addresses
> 
> Hello all,
> All our Dual-Stacked CentOS 7 boxes here at Lancaster have failed to renew their DHCPv6 leases over the weekend, so we're kind of dead in the water as our "state of the art" C7, v6 enabled SE has ground to a halt. It's also hurt our perfsonar boxes, and our bdii. But any box running SL6 is having no problems with it's v6 networking. It seems OS dependent. You can ping6 from the affected machines but you can't ping6 too them (they're not binding to their v6 address). Some packet sniffing seems to show the interfaces on these machines not getting any v6 DHCP ACKnowledgements.
> 
> I've dropped a mail to our central support guys asking if they've changed anything over the last week. But to get ahead of it our end I thought I'd approach the collective. Has anyone seen anything like this before?
> 
> To give a bit more information, Lancaster is running DHCPv6 rather then SLAAC, but I've never had any luck getting a C7 boxes v6 networking to work without disabling the Network manager. In fact when NetworkManager is enabled we saw exactly the same behaviour.  This setup has worked for long enough that I would have thought we'd have seen any issues by now (we've had dual-stacked perfsonars for a good few months, dual-stacked C7 DPM for a month and dual-stacked C7 BDII for a fortnight).
> 
> Any help or advice, or any idea of where to start,  would be greatly appreciated.
> 
> Thanks in advance,
> Matt, wondering  why things always break on a week off?
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