INFORM getting different values for the same option than REQUEST

Glenn Satchell glenn.satchell at
Tue Feb 16 06:44:04 UTC 2016

Hi Bob

I'm pretty sure this is expected behaviour. The INFORM request doesn't
have enough information for the server to work out pool memberships.

Try moving the dns server definition from the pool to the subnet.

I can't tell from your sample conf, but if you've got more than one pool
in that subnet then this won't help.


On Tue, February 16, 2016 8:19 am, Bob Harold wrote:
> I am seeing  a case where my DHCP server is sending different DHCP
> option values (for DNS Server) in response to an INFORM than it sends
> in response to a REQUEST.
> This particular DHCP range is set to use a different DNS server than
> the default.
> But an INFORM is getting the default DNS server instead of the
> specific value for the client's Dynamic DHCP range.  Is that correct?
> It was certainly not what I expected.
> The packet flow during a renew is:
> REQUEST from client
> ACK from server contains "Domain Name Server:"
> INFORM from client
> ACK from server contains "Domain Name Server:"  Why?
> Server:
> Internet Systems Consortium DHCP Server 4.3.1
> Client:
> Windows, gets DHCP IP
> dhcpd.conf is very long, the relevant bits (client's Client ID, MAC
> Address, and IP Address are not in the file):
> ...
> option domain-name-servers;
> ...
> subnet netmask
> {
>     option subnet-mask;
>     option broadcast-address;
>     ddns-rev-domainname "";
>     ddns-updates false;
>     option domain-search ...;
>     option routers;
>     pool
>     {
>         deny members of "DENY";
>         option domain-name-servers;
>         option time-offset 0;
>         range;
>     }
> }
> I obfuscated as little as possible.  And I normally list two DNS
> servers.  I did not ask why this user is using their own DNS for this
> subnet.  For now, my concern is whether this is expected or a bug.
> --
> Bob Harold
> DNS and DHCP
> University of Michigan
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at

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