[Dnsmasq-discuss] DHCP option 81 FQDN

[g***@mail.bg]

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) [1]



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.


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?


I try options like dhcp-option=81,0 and other variants, but with no
sucsess.




Links:
------
[1]
http://tools.ietf.org/html/draft-ietf-dhc-fqdn-option-13#section-3.2%29


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[Simon Kelley]

Post by g***@mail.bg
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.

Post by g***@mail.bg
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.

Post by g***@mail.bg
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.

Post by g***@mail.bg
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.