[CentOS] C7, encryption, and clevis

Fri Jun 8 17:39:36 UTC 2018
Valeri Galtsev <galtsev at kicp.uchicago.edu>

On 06/08/18 12:01, m.roth at 5-cent.us wrote:
> Valeri Galtsev wrote:
>> On 06/08/18 10:27, m.roth at 5-cent.us wrote:
>>> John Hodrien wrote:
>>>> On Fri, 8 Jun 2018, m.roth at 5-cent.us wrote:
>>>>> We've been required to encrypt h/ds, and so have been rolling that out
>>>>> over the last year or so. Thing is, you need to put in a password, of
>>>>> course, to boot the system. My manager found a way to allow us to
>>>>> reboot without being at the system's keyboard, a package called
>>>>> clevis. Works fine... except in a couple of very special cases.
>>>>> Those systems, the problem is that, due to older software, and *very*
>>>>> expensive licenses that are tied to a MAC address, I have to spoof the
>>>>> MAC address since my users got new(er) machines.
>>>>> Clevis is trying to contact its password server, using the *real* MAC
>>>>> address, but our DHCP has to serve the *spoofed* MAC address. I know,
>>>>> from trying, that I can't have two entries for the same system. Can
>>>>> anyone suggest a solution?
>>>> Nothing wrong with having two MAC addresses listed for one IP.  With
>>>> ISC DHCP the label for a host has to be unique, but the hostname doesn't.
>>> The IP's not the problem, it's dhcpd gagging on two entries, two MAC
>>> addresses, for the same server name - think dhcpd.conf.local
>> When I have a machine that can comes with different MAC addresses, and I
>> have to give it the same IP, here is what I have in DHCP server
>> configuration (Mac addresses and IP address are obfuscated below):
>> # tricky machine
>> host tricky {
>>     hardware ethernet xx:xx:xx:xx:xx:xx;
>>     fixed-address A.B.C.D;
>> }
>> # tricky machine again
>> host tricky1 {
>>     hardware ethernet yy:yy:yy:yy:yy:yy;
>>     fixed-address A.B.C.D;
>> }
> Hmmm... wonder if it will gag - we don't put the IP in that, that comes
> from DNS. The format we use is
>     host <host <shortname> P hardware ethernet <MAC address>; fixed-address
> <fqdn>;}

It will not care if you put hostname (FGDN) instead of IP address - 
either is acceptable in config file. FQDN just makes your DHCP server go 
for every request it receives where FQDN is involved to DNS server, 
whereas if you have static IPs (not rotating all the time Windows gang 
like to probably to make compromised machines change their IP all the 
time), then you will save unnecessary DNS requests and associated delays 
by using IPs.

> so if it would work, replace shortname with short and short1?

Yes, that was exactly John's point, I just put my example to make it 
more transparent: we all are quicker comprehending actual config files, 
than the documentations they were created according to.


>        mark
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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247