Info needed on when CNR updates DDNS

kevin_miller · ‎09-09-2008

Hello all.

I need to know if CNR updates DDNS only when a client gets an initial DHCP lease, or does CNR update DDNS also when a DHCP lease is renewed?

I need to know because we use AD for DNS and it does periodic DNS scavenging. I need to have my client names stick in DNS. I can make sure the scavenger interval is greater than the DHCP lease timeout, but that won't help if CNR doesn't re-submit the name to DDNS when a lease is renewed.

Thanks!

drolemc · ‎09-16-2008

When a DHCP client obtains the lease for the first time, the lease is for only one hour, even though the lease time in the policy is much longer. This happens only in scenarios where DHCP failover is used. In the failover scenario, the maximum client lead time (MCLT) is configured so that there is enough time for the backup server to synchronize with the main server. The recommended MCLT is one hour. This is needed only for new clients that are granted a lease for the first time, and is not applicable for lease renewals. After the initial one-hour lease is renewed, the client gets the lease specified in the lease policy. In CNR, customers can modify the MCLT to a lower or a higher value.

http://www.cisco.com/en/US/products/sw/netmgtsw/ps1982/products_qanda_item09186a0080094b10.shtml

http://www.cisco.com/en/US/products/sw/netmgtsw/ps1982/products_tech_note09186a0080094ec4.shtml#dhcp_config

kevin_miller · ‎09-16-2008

Thanks for the reply, but I don't think this is related to my issue. I probably did a poor job at explaining it. Here's another attempt -

We use CNR for DHCP, and AD for DNS. We currently use Solaris build #6.1.3.0510272135, but are now moving to 6.3.1.5. In my config, the CNR DHCP scope updates AD DNS for the forward zone when addresses are assigned. It also updates CNR DNS for the reverse zone. This works fine - both zones are updated and can resolve correctly. The problem is that the AD DNS server implements scavenging to remove stale resource records. In our configuration, after 14 days resource records that haven't been refreshed are removed from DNS.

The problem is that this process removes the records for other DHCP clients like non-Windows machines, older Windows PCs, and non-PCs - especially APs and printers. AD DHCP has an option to "Dynamically update DNS A and PTR records for DHCP clients that do not request updates", and this feature will re-do the DDNS update at every DHCP renewal so that the records of these machines are not scavenged. Does CNR DHCP do this? And if so, how is it configured?

kevin_miller · ‎09-16-2008

TAC helped me find the feature. CNR DHCP has an option called force-dns-updates which does exactly what I want. It is disabled by default. According to the docs - The feature controls whether the DHCP server retries a dynamic DNS update whenever a client renews its lease, even if the server thinks that the update was already completed successfully.