ISC DHCP - Two subnets on one physical interface.

I'm having some trouble trying to get dhcp to serve two subnets on one
interface.
The first is 10.0.0.0/24 which is for office workstations and
equipment. Everyone in here is assigned a static ip via mac address.
The second is a 'guest' network which is 10.0.10.0/24.

I was able to get dhcp to assign the ip address for both subnets by
making the subnet declaration 10.0.0.0/16. The problem is that there
are other settings that need to be set like the default route, dns,
netmask, etc.

In my first attempt, I made a pool and set all the settings to be that
of the guest network. I would then override those settings in the
host declarations for the office equipment. The problem is that it
didn't like having options such as routers,domain-name-servers, etc in
the host declarations.

Does anyone know how I can do this without a second NIC?

Below is my current config.
################ Current Config #################
max-lease-time 86400;
default-lease-time 14400;
ddns-update-style interim;

log-facility local4;

subnet 10.0.0.0 netmask 255.255.0.0 {
authoratative;
range 10.0.10.10 10.0.10.250; ## Guest Network

# don't let clients update A records for ddns
ignore client-updates;

# options
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.0.255;

option domain-name "domain.tld";
#option domain-name-servers 65.106.1.196,65.106.7.196;
#option routers 10.0.10.1;
option domain-name-servers 10.0.0.225;
option routers 10.0.0.1;

option ntp-servers 10.0.0.250;

option netbios-scope "";
option netbios-node-type 8;

host ws1 {hardware ethernet 00:13:21:d0:3f:0b;fixed-address 10.0.0.3;}
host ws2 {hardware ethernet 00:0d:9d:4c:94:4d;fixed-address 10.0.0.5;}
host ws3 {hardware ethernet 00:0d:9d:4b:35:bd;fixed-address 10.0.0.6;}
host ws4 {hardware ethernet 00:0b:cd:c3:ee:03;fixed-address 10.0.0.7;}
}
########################################

The following is what I would have liked to set up. Understandably
the following won't work because the two networks are not physically
separated, and there is only one NIC available for dhcp.


max-lease-time 86400;
default-lease-time 14400;
ddns-update-style interim;

log-facility local4;

subnet 10.0.10.0 netmask 255.255.255.0 {
authoratative;
range 10.0.10.10 10.0.10.250; ## Guest Network

# don't let clients update A records for ddns
ignore client-updates;

# options
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.10.255;

option domain-name "guest.domain.tld";
option domain-name-servers 65.106.1.196,65.106.7.196;
option routers 10.0.10.1;
}


subnet 10.0.0.0 netmask 255.255.255.0 {
authoratative;

# don't let clients update A records for ddns
ignore client-updates;

# options
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.0.255;

option domain-name "domain.tld";
option domain-name-servers 10.0.0.225;
option routers 10.0.0.1;

option ntp-servers 10.0.0.250;

option netbios-scope "";
option netbios-node-type 8;

host ws1 {hardware ethernet 00:13:21:d0:3f:0b;fixed-address 10.0.0.3;}
host ws2 {hardware ethernet 00:0d:9d:4c:94:4d;fixed-address 10.0.0.5;}
host ws3 {hardware ethernet 00:0d:9d:4b:35:bd;fixed-address 10.0.0.6;}
host ws4 {hardware ethernet 00:0b:cd:c3:ee:03;fixed-address 10.0.0.7;}
}

Dan wrote:
> I'm having some trouble trying to get dhcp to serve two subnets on one
> interface.
> The first is 10.0.0.0/24 which is for office workstations and
> equipment. Everyone in here is assigned a static ip via mac address.
> The second is a 'guest' network which is 10.0.10.0/24.
>
> I was able to get dhcp to assign the ip address for both subnets by
> making the subnet declaration 10.0.0.0/16. The problem is that there
> are other settings that need to be set like the default route, dns,
> netmask, etc.
>
> In my first attempt, I made a pool and set all the settings to be that
> of the guest network. I would then override those settings in the
> host declarations for the office equipment. The problem is that it
> didn't like having options such as routers,domain-name-servers, etc in
> the host declarations.
>
> Does anyone know how I can do this without a second NIC?



man dhcpd.conf

see shared-network

it's what's you need


>
> Below is my current config.
> ################ Current Config #################
> max-lease-time 86400;
> default-lease-time 14400;
> ddns-update-style interim;
>
> log-facility local4;
>
> subnet 10.0.0.0 netmask 255.255.0.0 {
> authoratative;
> range 10.0.10.10 10.0.10.250; ## Guest Network
>
> # don't let clients update A records for ddns
> ignore client-updates;
>
> # options
> option subnet-mask 255.255.255.0;
> option broadcast-address 10.0.0.255;
>
> option domain-name "domain.tld";
> #option domain-name-servers 65.106.1.196,65.106.7.196;
> #option routers 10.0.10.1;
> option domain-name-servers 10.0.0.225;
> option routers 10.0.0.1;
>
> option ntp-servers 10.0.0.250;
>
> option netbios-scope "";
> option netbios-node-type 8;
>
> host ws1 {hardware ethernet 00:13:21:d0:3f:0b;fixed-address 10.0.0.3;}
> host ws2 {hardware ethernet 00:0d:9d:4c:94:4d;fixed-address 10.0.0.5;}
> host ws3 {hardware ethernet 00:0d:9d:4b:35:bd;fixed-address 10.0.0.6;}
> host ws4 {hardware ethernet 00:0b:cd:c3:ee:03;fixed-address 10.0.0.7;}
> }
> ########################################
>
> The following is what I would have liked to set up. Understandably
> the following won't work because the two networks are not physically
> separated, and there is only one NIC available for dhcp.
>
>
> max-lease-time 86400;
> default-lease-time 14400;
> ddns-update-style interim;
>
> log-facility local4;
>
> subnet 10.0.10.0 netmask 255.255.255.0 {
> authoratative;
> range 10.0.10.10 10.0.10.250; ## Guest Network
>
> # don't let clients update A records for ddns
> ignore client-updates;
>
> # options
> option subnet-mask 255.255.255.0;
> option broadcast-address 10.0.10.255;
>
> option domain-name "guest.domain.tld";
> option domain-name-servers 65.106.1.196,65.106.7.196;
> option routers 10.0.10.1;
> }
>
>
> subnet 10.0.0.0 netmask 255.255.255.0 {
> authoratative;
>
> # don't let clients update A records for ddns
> ignore client-updates;
>
> # options
> option subnet-mask 255.255.255.0;
> option broadcast-address 10.0.0.255;
>
> option domain-name "domain.tld";
> option domain-name-servers 10.0.0.225;
> option routers 10.0.0.1;
>
> option ntp-servers 10.0.0.250;
>
> option netbios-scope "";
> option netbios-node-type 8;
>
> host ws1 {hardware ethernet 00:13:21:d0:3f:0b;fixed-address 10.0.0.3;}
> host ws2 {hardware ethernet 00:0d:9d:4c:94:4d;fixed-address 10.0.0.5;}
> host ws3 {hardware ethernet 00:0d:9d:4b:35:bd;fixed-address 10.0.0.6;}
> host ws4 {hardware ethernet 00:0b:cd:c3:ee:03;fixed-address 10.0.0.7;}
> }
>

Thank you. I don't know how I missed that in the man page. It was the
first thing I saw when I opened it. I think I got a little thrown off
when I saw so many sources (including isc's web page in certain
places) saying that you need 2 physical interfaces, but I knew it
could be done somehow.

For those who would like to see the working config.


max-lease-time 86400;
default-lease-time 14400;
ddns-update-style interim;

log-facility local4;

shared-network drlan {

subnet 10.0.10.0 netmask 255.255.255.0 {
authoratative;
range 10.0.10.10 10.0.10.250; ## Guest Network

# don't let clients update A records for ddns
ignore client-updates;

# options
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.10.255;

option domain-name "guest.domain.tld";
option domain-name-servers 65.106.1.196,65.106.7.196;
option routers 10.0.10.1;

host guest-conference-room {hardware ethernet
00:19:bb:d7:fe:d7;fixed-address 10.0.10.2;}
}

subnet 10.0.0.0 netmask 255.255.255.0 {
authoratative;

option subnet-mask 255.255.255.0;
option broadcast-address 10.0.0.255;

option domain-name "domain.domain.tld";
option domain-name-servers 10.0.0.225;
option routers 10.0.0.1;

option ntp-servers 10.0.0.250;

host office-ws1 {hardware ethernet 00:0d:9d:4c:
94:4d;fixed-address 10.0.0.5;}

}
}