Removing incorrect ddns info from lease

Chris Buxton clists at
Wed Nov 18 16:25:44 UTC 2015


Why do you think that removing the DHCID data from the lease will fix a DDNS issue? Have you diagnosed the issue? For example, are there multiple devices on the network with the same name?

If you're trying to overcome DHCP's DDNS optimization routine, you just need to set a global setting in dhcpd.conf. As I recall, the syntax is:

update-optimization false;

The DHCID record that goes alongside the A record in the DDNS updates for a lease is intended to uniquely identify the host that owns that name, by either cid or MAC address. It also indicates that the name is managed by DHCP. You do not want to remove the DHCID data from the lease.

Chris Buxton

Sent from my iPhone

> On Nov 17, 2015, at 8:47 AM, Frank Price <fprice at> wrote:
> Hi dhcp-users,
> Internet Systems Consortium DHCP Server 4.2.5
> IND 9.9.4-RedHat-9.9.4-18.el7_1.1 (Extended Support Version)
> dhcpd failover 
> I'm struggling with some of my clients occasionally losing their ddns entries, or not having them updated.  In an effort to fix things up, I want to remove DHCID info from the lease.  The dhcpd.conf man page tells me "data can be removed from the lease through operator intervention," but is light on details:
>> In addition to these differences, the server also does not update very aggressively.  Because each DNS update involves a round trip  to the DNS server, there is a cost associated with doing updates even if they do not actually modify the DNS database.  So the DHCP server tracks whether or not it has updated the record in the past (this information is stored on the lease) and does not  attempt  to update records that it thinks it has already updated.
>> This can lead to cases where the DHCP server adds a record, and then the record is deleted through some other mechanism, but the server never again updates the DNS because it thinks the data is already there.  In this case the data can be removed from the  lease  through operator intervention, and once this has been done, the DNS will be updated the next time the client renews.
> Here's one of the leases in question:
> lease {
>   starts 1 2015/11/16 21:31:22;
>   ends 2 2015/11/17 21:31:22;
>   tstp 3 2015/11/18 09:31:22;
>   tsfp 3 2015/11/18 09:31:22;
>   atsfp 3 2015/11/18 09:31:22;
>   cltt 1 2015/11/16 21:31:22;
>   binding state active;
>   next binding state expired;
>   hardware ethernet f8:bc:12:3f:69:90;
>   uid "\001\370\274\022?i\220";
>   set ddns-rev-name = "";
>   set ddns-txt = "31cce6d6ea09aa5603b3d319af3022007a";
>   set ddns-fwd-name = "";
>   client-hostname "yocto023";
> }
> Intuition says it's one of the ddns-* options, but my intuition often sucks. 
> 1.  What information should I remove from the lease?
> 2.  Is there a recommended way to do this that doesn't involve manually editing the leases file?
> Thanks as always for any help you can provide,
> -Frank
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