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How do DNS dynamic updates find the 'right' server?
Author: Cathy Almond Reference Number: AA-00653 Views: 7259 Created: 2012-04-04 10:04 Last Updated: 2017-05-03 11:46 0 Rating/ Voters

The way that clients (receiving their IPs via DHCP) or DHCP servers (handing out IP addresses) know which server to send DDNS updates to is by querying DNS for the SOA record of the domain to which the dynamic update should be made.  BY default, dynamic updates are sent to the master server in the mname field of the SOA record for the zone.

If using nsupdate manually or using scripting techniques you can specify the server to which dynamic updates should be sent.  Most DHCP servers (including ISC DHCP) also have configuration options for this.

If a slave for a zone receives a DDNS update for a zone for which it is authoritative, it's not going to update its zone data directly.  It will either discard it, or it will forward it to the master.  To make the slave forward the DDNS update, you need to configure allow-update-forwarding (see the Administrator Reference Manual for more detail) - this is not enabled by default.

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