dhclient -6 handling of IPv6 Duplicate Address Detection

Jiri Popelka jpopelka at redhat.com
Tue Apr 27 10:08:34 UTC 2010

On 04/27/2010 12:09 AM, Patrik Lahti wrote:
> Hi all,
> When assigning an IPv6 address a node performs Duplicate Address 
> Detection (DAD, RFC 4862). And as expected this is triggered by the OS 
> stack when dhclient -6 configures an address via the dhclient-script. 
> However, if the address is found to be duplicate, i.e. when DAD fails, 
> I don't see a Decline and an attempt to retry (RFC 3315, section 
> 18.1.8). It seems the dhclient goes on unaware of what occurred...
> Is this a known problem? With known solutions? Should dhclient handle 
> this, or is the intent that an outside entity (e.g. the 
> dhclient-script) do it? (is it ok to sleep in the script while DAD is 
> performed or will that mess up some dhclient timing)
> Regards and Thanks in advance,
> /P
> PS. I saw 
> https://lists.isc.org/pipermail/dhcp-workers/2010-February/000108.html 
> but couldn't find a response...

There's no response for my question(s), so I decided to do it my own way.

I implemented start_decline6() and do_decline6() functions which are 
called when
dhclient-script returns value indicating that DAD failed.
I put some sleep in the dhclient-script while DAD is performed and it
looks like it didn't break any timing.

I didn't send my patch to ISC yet, but I'm going to do it.
I just want to know if I should send it to dhcp-bugs at isc.org or 
dhcp-suggest at isc.org

Jiri Popelka

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