dhclient on Debian Jessie not sending the same identifier for DHCPv4 and DHCPv6 (RFC 4361)

Shawn Routhier sar at isc.org
Wed Sep 9 01:13:09 UTC 2015

> On Sep 8, 2015, at 3:51 PM, Nicolas C. <dhcp at nryc.fr> wrote:
> Le 08/09/2015 17:15, Shawn Routhier a écrit :
>> Try the -df option to the client.
>> This provides a method to share a DUID between the two clients.
> Thanks, it works when I manually start the DHCPv6 client...
> dhclient -6 -v -I -D LLT eth0
> ...and then the DHCPv4 client, with the "-df" option pointing to the lease file just updated by the DHCPv6 client...
> dhclient -4 -v -I -D LLT -df /var/lib/dhcp/dhclient6.leases eth0
> ...and in the forward zone, I have both records!
> dual-test.rfc4361.test. 300     IN      A
> dual-test.rfc4361.test. 187     IN      DHCID AAIBLNVQ2woWQBJ8+hS4pkoal+ezwugmTliSiuwzIbKb8ig=
> dual-test.rfc4361.test. 187     IN      AAAA    2001:660:3305:122::ec2
> Now the big question is : how can this be done automatically at bootup? I tried to delay the DHCPv4 client with this :
> auto eth0
> iface eth0 inet6 dhcp
> iface eth0 inet dhcp
>  pre-up sleep 5

The first thing to note is that the clients will save their DUID in their lease files, so once you
have gotten them to work on a given client it should continue to be happy, except if you
delete the lease file or the DUID from the lease file.

If there is enough of a gap in starting the clients then you can use -df with each of them pointing
to the other client’s lease file.  The first to start will create a DUID and put it into it’s lease file
and the second will pick up the DUID from that one.

If there isn’t enough of a gap then you might have to create your own DUID file for them to use.

> And a shell script /sbin/dhclient calling the real binary with correct options but it doesn't work, is it worth trying with a Debian Jessie without SystemD?
> I suppose it's a job for the maintainer of the "ifupdown" package in Debian?
> Cheers,
> Nicolas
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