Some details that might help identify my problem:
- I set ipmasq to start after services have been started using dpkg-reconfigure
- in /etc/network/interfaces, for eth0 I execute a script after eth0 is brought up. This script initializes iptables rules and ip masquerading.
- I use dnsmasq as DHCP and DNS server.
- The eth0 interface gets it's IP from a DHCP server by my ISP, eth1 has a static ip.