[NCLUG] DHCP Help

[Brian Talley]

On Thu, May 29, 2008 at 5:10 PM, Kyle Haefner
<Kyle.Haefner at colostate.edu> wrote:
> Hello all,
>
> I am trying to set up a dhcp server to serve multiple subnets from the same
> physical interface.  We have the routers proxy the DHCP request from the
> various subnets to this interface (10.174.0.11).
>
> The problem is that the DHCP server seems to ignore which subnet the request
> arrives from and seemingly haphazardly picks a subnet with which to service
> the request.
>
> If a request arrives via 10.174.44.1 it is given an IP such as
> 10.174.201.253. I can reserve IP address by MAC and it works, but is more
> overhead than this should be.
>
> Any ideas what I am doing wrong?

Based on what you are saying and the config below, a dhcp request that
comes in on an interface that is in the range of 10.174.0.11/32,
10.174.44.0/24 or 19.174.201.0/24 is going to receive a lease in
either the 10.174.44.0/24 or 19.174.201.0/24 subnets.  ISC DHCP server
will start vending the "highest" IP from the "highest" subnet - in
your case, the first lease would be for IP 10.174.201.254, the second
for 10.174.201.243, etc.

You need multiple shared-network declarations to do what you are
trying to do.  Each of these shared-networks needs a dummy subnet that
includes the relaying interface IP and then the subnet(s) from which
you want to vend.

The "relaying interface IP" is either going to be the first IP address
defined on the subnet-facing interface or the subnet-facing interface
IP address designated as "primary".

I can give a more detailed example if needed...

>
> Thanks!
>
> Kyle
>
>
> shared-network voip{
>
> #if I don't have this 'dummy' subnet dchpd fails to start
> subnet 10.174.0.11 netmask 255.255.255.255 {
> }
>
>
> subnet 10.174.44.0 netmask 255.255.255.0 {
>  range 10.174.44.12 10.174.44.254;
>  option subnet-mask 255.255.255.0;
>  option broadcast-address 10.174.44.255;
>  option routers 10.174.44.1;
>  option domain-name-servers 10.174.0.11, 10.174.0.12;
>  default-lease-time 86400;
>  max-lease-time 86400;
>  option tftp-server-name "10.174.0.11";
>
> }
> subnet 10.174.201.0 netmask 255.255.255.0 {
>  range 10.174.201.12 10.174.201.254;
>  option subnet-mask 255.255.255.0;
>  option broadcast-address 10.174.201.255;
>  option routers 10.174.201.1;
>  option domain-name-servers 10.174.0.11, 10.174.0.12;
>  default-lease-time 86400;
>  max-lease-time 86400;
>  option tftp-server-name "10.174.0.11";
>
> }
>
> }

-- 
Brian Talley
b225ccc at gmail.com ::: (970) 689 - 0108

"Chance favors the prepared mind." -- Louis Pasteur