tmark at isc.org
Wed Aug 15 10:54:05 UTC 2018
If you turn off conflict detection, then different clients attempting to
use the same FQDN can overwrite each other's DNS entries. Whether or not
you view that as a risk is up to you.
For DHCPv4 the DHCID is constructed from the client identifier option if
the client sends it, the MAC address otherwise. If your client always
sends the same client identifier regardless of the network it is on,
then the server should be able to update DNS entries for it as it roams
between networks and do so with conflict detection enabled.
ISC Software Engineering
On 08/14/2018 05:12 PM, Leroy Tennison wrote:
> I am getting a number of messages about "Forward map from <DNS name> to <IP adress> FAILED: Has an address record but no DHCID, not mine. In the logs I'm seeing these messages prior to this:
> "updating zone '<DNS zone for above name>/IN': update unsuccessful: <DNS name>: 'name not in use' prerequisite not satisfied (YXDOMAIN)" - using named-compilezone with -j I'm seeing that both an A and TXT record exist (we are using interim as the ddns-update-style).
> "updating zone '<DNS zone for above name>/IN': update unsuccessful: <DNS name>/TXT: 'RRset exists (value dependent)' prerequisite not satisfied (NXRRSET)".
> As best as I can tell, what is happening is the client is moving from a wired connection to a WiFi connection (for meetings) or vice versa. Initially I was looking for a way to make the MAC address rather than the system name the unique identifier for the system then I came across the update-conflict-detection parameter.
> Am I understanding the description correctly, if this parameter is set to off and the client "changes MAC addresses" (due to a switch to/from WiFi) then the dhcp server will remove the previous DDNS entry and replace it with the current one? Are there disadvantages to doing this?
> If that isn't the way to handle this situation, how can I make the MAC address (rather than the system name) the unique identifier for DDNS?
> Thanks for your help.
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> Leroy Tennison
> Network Information/Cyber Security Specialist
> E: leroy at datavoiceint.com
> 2220 Bush Dr
> McKinney, Texas
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