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I'm setting up a failover system for DHCP and DDNS. The software being used are ISC BIND and ISC DHCP, running on Ubuntu 10.04 LTS.

serverA runs DNS01 and DHCP01, serverB runs DNS02 and DHCP02. DHCP failover is set to a 128-bit split (half the zone on each server), wich is working correctly.

serverA is set as the master DNS, serverB is secondary (slave).

Where should DHCP02 point its dynamic updates? Can a slave zone be updated with DDNS entries and then be AXFR'ed back to the master, or do I need to point all DDNS updates to DNS01, both on DHCP01 and DHCP02?

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For those of you who want to suggest Windows DHCP+DNS: Microsoft requires CAL for each client, wich is out of the question. –  pauska Feb 16 '11 at 9:10

2 Answers 2

I have the following in /etc/dhcp/dhcpd.conf, on both servers:

ddns-update-style interim;

include "/etc/bind/rndc.key";
zone myzone.lan. {
    primary 192.168.81.10;
    key rndc-key;
}
zone 81.168.192.in-addr.arpa. {
    primary 192.168.81.10;
    key rndc-key;
}

And I copied the primary's /etc/bind/rndc.key file to the secondary DNS/DHCP server. This way, the dhcpd.conf file section above is exactly the same on both dhcp servers.

Alternatively, I could have copied the primary's DNS key to a different file, and specified that file in the dhcpd.conf file of the failover.

It seems to work, so maybe pauska's answer saying it's not doable is obsolete. I have this running on Debian Squeeze with isc-dhcp-server version 4.1.1-P1-15+squeeze2.

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-1 Completely not what the Question is asking... –  Chris S Mar 2 '12 at 19:05
    
@Chris: ???. The OP wants both his DHCP servers to update his primary DNS zone. Using the primary DNS key on both DHCP servers, and configuring them both to send updates to the primary DNS allows that. Seems to me that was exactly the original question. "Where should DHCP02 point its dynamic updates" : to DNS01. –  mivk Mar 2 '12 at 19:33
    
You're getting caught up in that one little sentence. He's really asking if multiple BIND servers can accept updates for a dynamic zone. The answer is no, which is what was already answered. The author was well aware of how to configure two servers to send updates. The Question is concerning failover ability within BIND for dynamically updated zones; which there is none. –  Chris S Mar 2 '12 at 19:41
    
Well, I still disagree. The last part of the question summarizes it: "or do I need to point all DDNS updates to DNS01, both on DHCP01 and DHCP02?" (the answer is yes). –  mivk Mar 2 '12 at 19:46
up vote 2 down vote accepted

Looks like this is not doable. I tried to lab it, and the secondary DHCP fails with errors in the syslog about not being allowed to update the zone.

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