In certain situations you may wish to install two network adapters into a RES HyperDrive appliance. For example, you may not want to route internal traffic via the same gateway interface as external traffic. In this scenario there are some things that you need to be aware of. The RES HyperDrive documentation intimates that the primary NIC is the internet facing interface.
This isn’t necessarily the case and either NIC can be used. What you do need to be aware of though, is that if you configure a default gateway on all NICs, CentOS 5.3 will use the highest interface gateway as the default route. Therefore, if you specify a default gateway on both NICs in multi-homed deployment, the eth1 gateway will be used for the default route. If you look closely at the example above you will notice (there are 2 x 10.0.1.1 firewalls!) that the eth1 interface has no gateway specified. I recommend that you do leave the internet facing NIC with the default gateway, but whether this is eth0 or eth1 is up to you.
If you wish to manually alter the IP addressing information you can find the configuration scripts in the /etc/sysconfig/network-scripts/ directory. There will be an ifcfg-eth0, ifcfg-eth1 for each attached NIC. Use your favourite text editor to update the appropriate file.
Once you have configured the correct IP address(es) and gateway you will need to add static routes to the “internal” network(s). The RES HyperDrive CentOS installation stores static routes in the route-<interface> file in the /etc/sysconfig/network-scripts/ directory. As an example, if our internal networks were 172.16.0.0/255.255.0.0 and 172.17.0.0/255.255.0.0 we would create the following entries in the /etc/sysconfig/network-scripts/route-eth1 file (assuming the internal gateway is actually 192.168.1.1 and not 10.0.1.1!):
172.16.0.0/16 via 192.168.1.1 dev eth1 172.17.0.0/16 via 192.168.1.1 dev eth1
Once you’ve made all your changes you can restart the networking stack by running the service network restart or reboot the appliance. If you want to view the routing table, just run the route command. Simples!