[Dibbler] question concerning dibbler-server using unicast option.

Tomasz Mrugalski thomson at klub.com.pl
Thu Dec 3 08:30:57 CET 2009

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.


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