nsupdate from a dhclient

David W. Hankins David_Hankins at isc.org
Tue Sep 26 20:23:48 UTC 2006

On Tue, Sep 26, 2006 at 12:48:37PM -0400, Ralph Blach wrote:
> Is there a way to get dhclient to use nsupdate update the A ptr of the DNS
> server instead of using the the DHCP server to do it.

See 'man dhclient.conf', search forward for "DYNAMIC DNS".

Note that it is known to not work on most Linux platforms that
have applied a chroot/setuid form of protection (they apply a
constraint so the client may not open the UDP socket it needs
to send updates...you get a weird 'permission denied' error).

> Also, in the dhclient.conf file, is there a way to specify the maximum lease
> time which will be allowed.
> So if a dhcp server supplied the cleint with a leas time of 8 days, then a a
> lease time of 1 day would be used?

You mean you want to elect a lower maximum renew time.  I'm not sure
why that would be useful.

If you "send dhcp-lease-time x;", the remote server should try and give
you the nearest time its configuration allows near that value 'x'.  If
it gives you an 8 day lease time anyway, then you get an 8 day lease

I'm not sure what problem you're trying to solve by pretending the
lease time is shorter.  It does not sound wise to record something
other than what the server specified, even if it does sound safe
to utilize lower values.

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David W. Hankins	"If you don't do it right the first time,
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