Shared Network Configuration

Sean Higgins seanhiggs at
Thu Nov 8 19:46:33 UTC 2007

Hi Folks,

Hoping some of you  can help me out on this.
I am  hoping to use an ISC server on a flat network(single broadcast
domain) to assign addresses for two separate subnets. The first subnet
is private(RFC1918) and NAT'd at the router for internet access. The
second subnet is public and will be assigned to VoIP terminals based
upon dhcp client identifier.

What I would like to do is assign global parameters as per usual and
then create a client class by matching client identifier. From there
create  a shared-network declaration with the public and private
subnets defined and within the public subnet create a pool which only
allows members of the client class defined earlier. All other clients
would (hopefully) be assigned addresses from the other subnet. I have
attached a very hurried example to illustrate the concept below. With
the understanding that some of the syntax is probably incorrect , I
would really appreciate some guidance as to whether the basica concept
is OK or if my thinking is fundamentally flawed.

Thanks in advance.

Sean Higgins

Sample config to illustrate concept.

# File name: dhcpd.conf
# Global option definitions common for all supported networks...
default-lease-time 300;
max-lease-time 7200;

# Declaring a class for VoIP terminals

class "voip-clients" {
  match if substring (option dhcp-client-identifier, 1, 3) = "voip";

# Declaring a shared network
# This is to accommodate two different subnets on the same
# physical network; see dhcpd.conf.man5 for more details
shared-network "Network"
# Declaring subnet for public clients
subnet netmask
# Pool addresses for i2004 clients
allow members of "voip-clients";
option routers ;


# Declaring subnet for private clients
subnet netmask
option routers;



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