Retaining information between DHCP requests
Dave.Close at us.thalesgroup.com
Wed Oct 8 17:26:56 UTC 2014
I understand that dhcpd doesn't record requests for static addresses in
the leases file, and that makes sense to me. But without that recording
I'm at a loss of how to save information between requests.
The problem I'm trying to solve is to provide different nameserver
values to the same machine under different circumstances. In particular,
I need a different nameserver configuration when the machine is being
installed, via PXE kickstart, and during normal operation. The machines
are running Fedora but that may not be important.
During installation, kickstart seems to exchange messages with dhcpd
three times. The first time it goes through the full DISCOVER, OFFER,
REQUEST, ACK sequence. The second and third times it only sends REQUEST
and gets ACK. All responses give it a full-day lease.
The DISCOVER and REQUEST messages in the first exchange include a unique
vendor-class-identifier starting with "anaconda". I can and do detect
that string and provide the special nameserver response needed. But the
subsequent REQUESTs do not include that string and dhcpd then provides
the normal operation response. That confuses kickstart and the
(I'm also puzzled why kickstart would send the subsequent REQUESTS,
given that it was told it had a full-day lease. But I probably can't do
anything about that.)
Ideally, I'm looking for a way to remember the status of the most recent
DISCOVER/OFFER and to continue to use that to determine the response to
any subsequent REQUESTs. But, because these machines have static
addresses, I can't record anything in the leases file. Is there any
other solution that anyone can suggest? Is there a way I can add
something to the OFFER that would always be included in a later REQUEST?
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