How to change the netmask and gateway on a solaris sunfire server
To change the subnet mask, edit this file: /etc/netmasks
and changed the subnet mask to what you require.
Next, to change the default gateway, edit this file:
/etc/defaultrouter
and I changed the default gateway to what you require.
Lastly, reboot the box when you are completed and then go back and view that the chnages are still there...