DDNS updates for secondary DNS server

glenn.satchell at uniq.com.au glenn.satchell at uniq.com.au
Wed Apr 28 00:42:09 UTC 2021

Hi Kraishak

I had a look in the dhcpd.conf man page, and the description there is a 
bit ambiguous, so I don't know what it meant to happen:

     The  primary  statement  specifies  the  IP address of the name 
     whose zone information is to be updated.  In addition to the primary
     statement there are also the primary6 , secondary and secondary6 
     The primary6 statement specifies an IPv6 address for the name 
     The secondaries provide for additional addresses for name servers to
     be used if the primary does  not  respond.

Some suggestions of things you could try:

- Check your secondary is configured to accept updates from the dhcp 
- Turn on logging of updates on the secondary to see if anything is 
- Run a packet trace on the secondary to look at network traffic to see 
if anything is sent to it.

I think the next step after that is to have a look at the dhcpd source 
and see what the code actually does in this case.

It may also be worth asking the question on one of the BIND9 mailing 
lists about whether a secondary can accept dynamic updates and what 
configuration options are required to do this. There is also the BIND 9 
Administrator Reference Manual which may be useful.

Also something to think about is the scenario where the primary is down 
and the secondary receives an update. What happens when the primary 
returns? It won't have the update and either it will overwrite the 
secondary's zone file with the primary (removing the updated record) or 
it won't but then the primary won't have that record and the secondary 
will. This means where the primary and secondary have different values 
for the same record or one of them does not have the record.


On 2021-04-27 19:30, kraishak wrote:
> Hi Glenn
> Thanks for reply,
>  zone example.com.
>         {
>             primary;
>           secondary;
>         }
> I don't, think it tries to ever update the secondary
> -----> So in a sample zone section adding secondary statement is of no
> significant even if we add the valid secondary DNS server it will send
> updated only to primary and if primary is down it will throw exceptions
> unable to add forward/reverse map but it won't use the secondary server
> definition from the zone section in dhcpd.conf, Please correct me if I 
> am
> wrong.
>  Also looks like something in your DNS config may not be quite right. 
> In
> dhcp your primary is, but it is trying to update
> and gets an error.
> ----> was the client IP which the DHCP server gave to the
> client from scope range
> In a valid case when the primary is up, I am getting messages like 
> below
> Added new forward map from n0001-000001.example.com to 
> where
> was the client IP
> so I guess it is not issue with config
> Thanks
> Kraishak
> --
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