[Dibbler] Problems assigning DNS on ppp interface

Tomasz Mrugalski thomson at klub.com.pl
Fri Mar 16 10:49:34 CET 2012

On 16.03.2012 01:13, Steve Phillips wrote:
> Hey there,
> I am in the process of setting up a VPN server to allow clients to be
> assigned both an IPv4 address as well as a global /64 IPv6 address, this
> all worth with varying levels of reliability, however, trying to assign
> IPv6 DNS addresses has gotten me completely stumped.
> The server is a linux box running dibbler-server 0.8.2
> The client is a windows 7
> the VPN client is just the built in vpn adaptor found with windows and
> set to pptp mode
> I started off with the stateless option and just trying to pass back the
> DNS server address.
> log-level 8
> log-mode syslog
> stateless
> iface ppp0 {
>   option dns-server 2001:49f0:1025::10
>   option domain focb.co.nz
>   option lifetime 500
> }
> However, this didn't seem to work, so I tried to setup stateful
> allocation by adding a class
"Didn't seem to work" is awfully vague. What does the client logs say
(there should be dibbler-client.log file)? Client claims to have sent
SOLICIT messages correctly? How are you running your client? If you
start your client before the link is up, client will simply complain
that specified ppp0 is not present and quit (btw is your interface
really named ppp0? It sounds very unixy). Different configs you listed
do not help much if your client can't get to the server.

Have you tried running the client from console (dibbler-client run,
rather than dibbler-client start)? This will give you all the details.
It is good that you are running on maximum (8) logging level.

If your client happen to complain that interface is not ready and just
quits, you may want to try inactive-mode. See section 4.18 of User's
Guide. This mechanism was invented for cases like these. If your
interface is not up, dibbler will wait couple of seconds and try again,
rather than simply giving up. Inactive mode is an equivalent of trying
to start client every 10 seconds manually.

> It appears that no DHCPv6 traffic is even happening on the link once it
> comes up, but it's difficult to see the initial negotiations due to the
> dynamic nature of the link (tcpdump doesn't like to operate on an
> interface that isn't there :-) )
That's not a problem. Client will retransmit SOLICIT that remain
unanswered using exponential backoff algorithm: after roughly 1, 2, 4,
8 etc. seconds. If you leave it up there without any answers, it should
eventually hit the upper bound of about 120 seconds intervals. It is
trivial to use tcpdump here: establish ppp link, start tcpdump, then
start client.

> I tried to tell windows to /renew6 the tunnel interface, but got an
> error stating "the operation failed as there is no adapter in the state
> permissible" when using the interface ID to force a renewal.
That is a different mechanism, offered by windows stack itself. Dibbler
is a separate software and cannot use said mechanism. This is just pure
speculation, but perhaps windows run its own dhcpv6 client? If you want
to use dibbler, make sure that you disable windows' own DHCPv6 client.

> I suspect that windows is simply not trying to send an
> INFORMATION_REQUEST message on the ppp link (or indeed, an other type of
> dhcpv6 message) but am not too sure why this would be.
I never heard about anyone running on ppp link on Windows.

You never showed client log file. One of the first things client does is
interfaces discovery. It should list detected interfaces, together with
some information about them (name, link address, flags etc). Client
should also write down client-IfaceMgr.xml, which is XML representation
of the intefaces it was able to detect. I suggest looking at that file.

> From reading back through the archives, it seems that a few people HAVE
> gotten something similar to work (VPN server, radvd to assign a prefix
> via RA and then DNS over ppp0 with dibbler ) - what did you do on the
> windows client side to get this working ?
I recall people have Dibbler working over ppp, but I do not recall
Windows being mentioned in that context.

> Either that, or is there something in my config that is wrong ?
Configs looks ok.

> Please help, I'm busy going hairless here :-)
To summarize:
1. run client in console. Make sure that it is really running.
2. send your client-IfaceMgr.xml
3. send your client log.

Hope that helps, at least a bit.

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