[CentOS] C7, encryption, and clevis

Fri Jun 8 16:37:00 UTC 2018
Valeri Galtsev <galtsev at kicp.uchicago.edu>

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;

# and a bunch of other configs for the same machine

The only trouble here will be if both MAC addresses request IP and and 
are both present, in that case DHCP server will offer that same static 
IP to the second request from different MAC address as well, but DHCP 
client (if smart) will check the presence of the IP address on the 
network already, and will not use that IP if it is already used and will 
send new request, and this will go on till first hardware stops using 
that IP address.

Those are "tricky", "tricky1", ... labels that John mentioned should be 
unique, and they are only known to DHCP server.

  There are a bunch of Out Of Band management creeps that sit on the 
first network interface and come up when AC is connected no matter 
whether the system is up or not. And they come with different MAC 
address. And these are the ones that you can not assign the same IP as 
that the machine itself is supposed to have. Sorry about little rant, 
these creepy things are sysadmin's disaster, - UNIX sysadmin's disaster 
I meant. Or Windows sysadmin's best friend, I figure. Like in the phrase 
I'm stealing from one Windows sysadmin whom I respect a lot: "Did you 
try to power cycle the machine and see if it solves that?"

I hope, this helps.


>       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