variables in configuration

Nenad Tomasevic Nenad.Tomasevic at
Tue Jun 30 18:47:54 UTC 2009

This looks really good and simple, like all other good solutions, i was going in completely wrong direction.. :)) Well, i'm blonde and not developer.. :))
Thank you very much, i'm going to try that tommorow and get to you/everyone else the results.

Does anbody have experience with similar configurations and how that kind of setup reflectes on hardware, specially cpu usage?
The reason i want that in the first place is large number of clients, i'm talking about hunderds for start, later maybe thousands..


-----Original Message-----
From: dhcp-users-bounces at on behalf of Rask, Curt
Sent: Tue 6/30/2009 7:07 PM
To: 'Users of ISC DHCP'
Subject: RE: variables in configuration
So, to summarize your intent, it sounds like you want to dynamically generate a bootfile name based off of something learned from the DHCP Discover / Request, in this case the Circuit ID and Remote ID from option 82.  One way to accomplish this is to use something like the following:

        option bootfile-name = concat((option agent.circuit-id),".",(option agent.remote-id),".cfg");


-----Original Message-----
From: dhcp-users-bounces at [mailto:dhcp-users-bounces at] On Behalf Of Nenad Tomasevic
Sent: Tuesday, June 30, 2009 8:31 AM
To: dhcp-users at
Subject: variables in configuration


I'm trying to get configuration file which will be assigning config files to clients based on predefined variables, more precise based on option 82 parameters in the dhcp request, so, if in dhcp request the option agent.circuit-id is "switch01" and option agent.remote-id is "01", the bootfile-name in dhcp offer will be "switch01.01.cfg".

here is my lame attempt to do that, dhcpd.conf;


agent-id="option agent.remote-id";
circuit-id="option agent.circuit-id";

#local subnet
subnet netmask {

  option subnet-mask;
  option routers;
  option tftp-server-name "";
  option bootfile-name "$circuit-id.$agent-id.cfg";

  default-lease-time 259200;
  max-lease-time  518400;

and that don't work, dhcp offer takes $circuit-id.$agent-id.cfg as bootfile-name, suprise, suprise (actually, i'm showing you the file only to make my idea more understandable)... :))

question is, is it possible to make such thing and if it is, in which direction I must look to achieve that?
point of the hole thing is to make dhcp server with 100% uptime because it wont need restart every time when configuration is changed.


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