[Dibbler] Dibbler FQDN+TA version

Tomasz Mrugalski thomson at klub.com.pl
Wed Jun 28 20:11:44 CEST 2006

On Wed, 28 Jun 2006 somebody known as Karl Auer wrote:

> I've just started getting to know Dibbler - very nice! I have been most
> impressed with how easy it is to compile (on Ubuntu breezy), and how
> easily the WindowsXP binaries installed and worked.
That's nice. Dibbler is being developer under Debian and Ubuntu is very 
similar (lots of packages are common). I also did my best to write 
portable code, so Dibbler should compile without problems on various 

> However, I very much want to use DDNS, so I grabbed the FQDN+TA version.
> However, short of reading the source code, I can't figure how it is
> supposed to work.
That's why it is not officially released. Support is experimental and 
lacks any kind of documentation. But this is going to change soon.

> Does anyone have a sample client and sample server config file,
> preferably commented, that I could use as a stating point? The sample
> files included don't make sense to me.
There are none at this time. But since there's at least one person (i.e. 
you), who is interested in, I'll prepare improved version with docs. I'll 
do that in this weekend, so expect new version around 2nd July.
This will be a development version, not a stable one. Do you need windows 
version, too? It would be great if you could check if everything works in 
Windows, as my testing capabilities under windows are rather limited.

> Also, is a FQDN+TA client version of the software needed, or is the
> "standard" Dibbler WinXP client enough?
Development (fqdn+ta) version is required. Take note that at this time, 
only client is able to perform updates.

> When I say DDNS, I mean this:
> - the client has a name (FQDN) that it wants to use:
Client will obtain name, but will not set it in system. This can be fixed 
quite easily.
> - it sends that name to the server as part of its request
hmmm, it can send its name to the server as a hint only. Server can take 
this into consideration or ignore this hint completely and provide other 

> - the server allocates an address to the client
This is done via IA option and is supported for a looong time.

> - the server does two dynamic updates to register the name
>   (forward lookup) and the address (reverse lookup) in the DNS.
In fact, FQDN specs say that it is a matter of negotiation between server 
and client, who will perform update. Currently only forward update is 
done (AAAA record). But I suppose it is easy to extend the code to perform 
also reverse update.

> - when the lease expires, the server does dynamic updates to
>   remove these entries from the DNS
That will be more problematic. When client shuts down, it will remove its 
name from DNS. However, when client has crashed, went out of range or a 
power failure occured, this update will not be performed. But if I 
understand DNS Updates mechanism correcly, each record has its own TTL. 
When this TTL expires, DNS will remove this record by itself. Did I get it 

I'd also like to write a few words about server/client DNS updates. From 
the security point of view, it is better to let server perform all 
updates. DNS configuration is simpler, as there is only one IPv6 address 
which is allowed to perform updates. On the other hand, this approach does 
not scale well. When there are hundreds of clients, server might not be 
able to keep up or will slow considerably. Of course this disadvantage can 
be minimised by cleverly designing server architecture. (separate thread 
for each update?)

Other approach is to let clients perform updates on their own. This scales 
well, because DHCPv6 server must only provide additional option, which is 
quite easy. But DNS server must allow to perform updates from a whole 
address class. This might seem security risk at first glance, but bind9 
can be configured to allow updates in one domain only.

Hey, people! What do you think? Should dibbler support both methods? Or 
the client-side update only?

Hope that helps.

Tomasz Mrugalski,              | "I think there is a world market for     |
thomson(at)klub(dot)com(dot)pl |  about five computers."                  |
                                |     Thomas J. Watson (Chairman, IBM) 1943|

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