[Dibbler] question concerning dibbler-server using unicast option

Keshi LI (gmail) keshi.li at gmail.com
Thu Dec 3 15:06:43 CET 2009

Thanks for your reply, Tomek.
Indeed, RFC3315 section 18.1 implied that, to one client, server sending
only once with server unicast option should be enough.

concerning why I set the gobal IP addr on myclient manually in the first
place, it is because I also saw the following issue when I did the "general
case" as you mentioned in your mail.

I don't set global IPv6 addr on myclient,
I configured dibbler-server to use server unicast option and use 2000::1

myclient send Solicit from its link-local addr to ff02::1:2
dibbler-server send Advertise from 2000::1 to myclient's link-local addr

The problem is that myclient doesn't know the route to 2000::1 yet, so it
doesn't even send any Request to the wire.
I think dibbler-server should send Advertise from it's link-local addr i.s.o
global addr, I'm I correct?


> Message: 3
> Date: Thu, 3 Dec 2009 08:30:57 +0100 (CET)
> From: Tomasz Mrugalski <thomson at klub.com.pl>
> Subject: Re: [Dibbler] question concerning dibbler-server using
>        unicast option.
> To: Dibbler users list <dibbler at klub.com.pl>
> Message-ID: <alpine.DEB.1.10.0912030815190.23265 at v13.klub.com.pl>
> Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII
> On Wed, 2 Dec 2009 somebody known as Keshi LI (gmail) wrote:
> > Hi, All:
> >
> > I'm using Dibbler-server 0.71 on Ubuntu. When testing my DHCPv6 client, I
> > see the following behavior:
> >
> > I configure dibbler-server to use unicast option like this:
> >
> > iface "eth2" {
> > unicast 2000::1
> > ....}
> >
> > And I configured myclient with IP 2000::2 and dibbler-server with IP
> 2000::1
> >
> > myclient sends Solicit from its link-local addr to ff02::1:2
> > dibbler-server Sends Advertise with Server unicast option from 2000::1 to
> > myclient's link-local addr->OK
> > myclient sends Request from 2000::2 to 2000::1 ->OK
> > dibbler-server sends Reply from 2000::1 to 2000::2, but this reply does
> not
> > contain "Server Unicast Option" ->?????????
> >
> > Is this a bug of dibbler-server or am I understanding the protocol wrong?
> > I thought once I configured Unicast on server, server should send all
> > messages with "Server Unicast option", not only the first message.
> Why would server send the same option over and over again? Once it
> announced its unicast address, client should remember it (the same way as
> it remember server DUID) and use it.
> Can you point to exact place in RFC3315 that tells that server SHOULD
> or MUST send unicast in every response? I think the most relevant
> paragraph is RFC3315, section 18.1:
>    If the client has a source address of sufficient scope that can be
>    used by the server as a return address, and the client has received a
>    Server Unicast option (section 22.12) from the server, the client
>    SHOULD unicast any Request, Renew, Release and Decline messages to
>    the server.
> I think you should modify your client to act accordingly.
> Regarding unitast, there another nuance. You are doing kind of shortcut by
> setting your client with 2000::2 address, so its communication with
> unicast is simple. However, in a general case, client has only its
> link-local address configured when initiating DHCPv6 exchange. It sends
> solicit and receives unicast option in advertise. Unfortunately, client
> does not have address with sufficient scope (global) to communicate with
> announced unicast address, so it may still send request message to the
> usual link-local multicast. After reply is received, client receives its
> own global address and is finally capable to do unicast communication. So
> actually the first unicast message is usually RENEW.
> That's how dibbler client is expected to behave.
> Cheers,
> Tomek
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