Dyn DNS...masters and slaves...
b19141 at achilles.ctd.anl.gov
Tue Sep 5 14:37:08 UTC 2006
"Kevin P. Knox" <bind-users at rc4systems.net> wrote:
>I've recently had the occasion to configure dynamic DNS on my current
>employer's networks to support MS AD. We're running BIND 9.2.4 on Debian 3.1
>(stable). Other than having no support for GSS-TSIG, it's working well so
>far. I do have a question though.
>It "seems" that with dynamic DNS on BIND, there is single point of failure.
>MS clients find the authoritative server by looking at the MNAME field in the
>SOA RR for the zone to update and that field should always be the master
>server. I know that slaves can forward updates if so configured, and we've
>configured IP based ACLs to permit this. But I have yet to see a client send
>an update to a slave.
>What if the master DNS server becomes unreachable to clients needing to
>perform updates? I'm having trouble finding information explaining the
>mechanics of this. I've got a current copy of the BIND ARM, and DNS & BIND,
>5th Edition. If somebody could point me in the right direction for answers,
>I'd certain appreciate it. Thanks. :-)
If the master is unavailable when a client needs to perform a DDNS
update, then, obviously, the update can not be performed. If the update
is from a DHCP server, then the DHCP server may queue the request and
retry later. I do not know what the DHCP RFCs have to say, if anything,
on this subject. If the update is a self-registration from a Windows
PC, then I do not know if the Windows code will retry later. I believe
that the self-registration code will re-register once a day to insure
that the records in DNS have not "mysteriously" disappeared.
As for sending updates to slave servers - I see a number of DDNS updates
being sent to my slave servers. I assume that the packets come from
DHCP servers, but I do not know what DHCP code is being run. I believe
that RFC 2136 (DDNS) states that the packets must be sent to the master
server. If a packet were to be sent to a BIND slave server, and that
server were configured to forward the request to the master, and the
master server were unavailable, I do not know if BIND would queue the
request or discard it. I have not looked at the latest BIND code.
Barry S. Finkel
Computing and Information Systems Division
Argonne National Laboratory Phone: +1 (630) 252-7277
9700 South Cass Avenue Facsimile:+1 (630) 252-4601
Building 222, Room D209 Internet: BSFinkel at anl.gov
Argonne, IL 60439-4828 IBMMAIL: I1004994
More information about the bind-users