DHCP server not routing to connect to internet for clients

Solution 1:

In /etc/network/interfaces do not specify a broadcast or gateway. This is done with the dhcp lease. You do need to specify a network for the DHCP however. This will configure eth1 to run on the 192.168.10/24 network. eth0 will be your gateway which is connected to your primary DHCP router. Change it to this -->

auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
     pre-up iptables-restore < /etc/iptables_rules
auto eth1
iface eth1 inet static
address 192.168.10.1
netmask 255.255.255.0
network 192.168.10.0

Then your dhcp.conf file will specify the routers and gateways. Use the DNS IP adresses in your /etc/resolv.conf file. These are known to be suitable in your location with your ISP. Change the routers and DNS settings in your DHCP.conf to this -->

option routers 192.168.10.1;
#8.8.8.8 is google's public DNS server (this is optional)
#Include the DNS IP addresses in your /etc/resolv.conf file
option domain-name-servers 8.8.8.8, (IP addresses in your /etc/resolv.conf)

Note: If you want to save your iptables rules, than after you set them, run this command to save it to a file --> iptables-save > /etc/iptables_rules You can see the placement to load the rules in the /etc/network/interfaces settings I provided. This will happen when the network manager is loaded/reloaded.

Let me know if this helps.