[Dnsmasq-discuss] DHCP option 81 FQDN

[Simon Kelley]

On 20/11/11 21:30, glesov at mail.bg wrote:
> Hi,
>
> I have trouble with DHCP option 81 - FQDN. I want to use dnsmasq as DHCP
> server, but I want Windows XP client to update MS DNS server (AD
> integrated).
>
> Win Xp clients in DHCP:Request send option 81, with flags 0000-0-0-0-0
> (MBZ-N-E-O-S), i.e. client will be responsable for DDNS update.
>
> But in response (ACK) from DHCP server, these settings is overriden -
> flag is 0000-0-0-1-1 - flag O is 1 - server has overriden client's
> preference for bit S, and bitS is 1 ("If the "S" is 1, the DHCP client
> SHOULD NOT initiate an update for the name in the server's returned
> Client FQDN option Domain Name field" -
> http://tools.ietf.org/html/draft-ietf-dhc-fqdn-option-13#section-3.2)
> <http://tools.ietf.org/html/draft-ietf-dhc-fqdn-option-13#section-3.2%29>
>

The thinking behind this is that dnsmasq doesn't support DDNS, so a 
client which attempts to update the (dnsmasq) DNS server via the DDNS 
protocol is bound to fail. If dnsmasq honours the S bit and doesn't use 
the FQDN, and then the client can't update via DDNS, then the name is 
lost. I confess I never though about a client updating a _different_ DNS 
server. It would be quite easy to add an configuration option to change 
this behaviour.

> dnsmasq version is 2.46
>
> I have another router in another site with version 2.2x(i dont know),
> and there server's option in ACKreply are 0-0-0-1 - only bit S is 1 -
> may be incorrect combibnation, but clients update their DNS.
>
Yes, that was a bug, forcing S to one, should set the O flag too.


> All domain-names are same, in dnsmasq options (domain-name) and win clients.
>
> Is there option to force dhcp server not to override client's preference
> in DHCP option 81 - FQDN?

No, but I'll look at adding one. If you're happy to patch the code and 
rebuild, I can point you to a very simple change to get things working 
for now.
>
> I try options like dhcp-option=81,0 and other variants, but with no sucsess.

I can't see a way to do it with the current code.


Simon.