Proper use of "allow/deny unknown-clients"?

Warner, Bill bill.warner at
Fri Aug 23 18:56:25 UTC 2013



How can I split a sting based on a field separator.  I've been using
option82 tags from the switch to help automate booting my big data (Hadoop
and cassandra) nfs/ramdisk root clusters.  The circuit-id comes to me in the


Of which I can use a line in dhcp.conf like:

                option host-name = substring(option agent.circuit-id, 0, 8);

to automatically assign the hostname on boot.


To optimize operations we've changed the hostname convention slightly to the
effect of:


So the substing command wont pick up the correct hostname any longer as it
will include the ':'


What might I be able to do in order to split this string on the ':' rather
than start poing and number of chars?





From: at
[ at] On
Behalf Of John Miller
Sent: Tuesday, August 20, 2013 11:19 AM
To: Users of ISC DHCP
Subject: Re: Proper use of "allow/deny unknown-clients"?




On Tue, Aug 20, 2013 at 1:57 PM, Chris Buxton <clists at>

On Aug 20, 2013, at 10:54 AM, John Miller <johnmill at> wrote:

> We're running into a seemingly odd issue:  when we specify "allow
unknown-clients" within one of our address pools, known clients are no
longer to obtain IP addresses.  When we remove the allow/deny rule
altogether, there's no problem with either known or unknown clients

If you set an "allow" rule, anything not allowed is implicitly denied.

If you set a "deny" rule, anything not denied is implicitly allowed.


Ahh... that makes sense.  I'd been making the assumption that since giving
no allow/deny directive allowed everything, that an explicit allow rule
wouldn't change that behavior.  Sounds like this is not the case.

Appreciate the help, Chris.


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