I am changing our ip address range from 172.19.50.x (255.255.255.0) to 172.16.y.x (255.255.252.0) - reason - more numbers.
Well, 172.19.x.x is a 'class B' IP address, so if you use it with no subnet mask at all (ie the default which would be 255.255.0.0 for a class B) you have 65535 potential addresses available to you, in the range 172.16.0.1 -> 172.16.255.254 (172.16.0.0 being considered as the 'network' and 172.16.255.255 the broadcast address). So one option is just to remove the subnet mask completly - but be warned, you would have to do this on all machines in one go - you can't run with subnet masks on some and not on others ... Is this an option ?
However, while moving over I need to let machines on both ranges communicate eg. clients printing to print servers etc.
It should be, as long as all of your networking uses the IP protocol (ie Samba/Windows networking on IP - not netbeui)
If I set up 2 interfaces on the server (derby) with ifconfig eth0:0 172.19.50.2 netmask 255.255.255.0 ifconfig eth0:1 172.16.0.2 netmask 255.255.252.0
what is the output of $netstat -nr on this box ?
and turn ip forwarding on with yast, should machines on the 2 ip ranges be able to communicate. eg. ping each other
You need to ensure that all machines are using either 172.19.50.2 (on the 172.19.50.0 network) or 172.16.0.2 (on the 172.16.0.0 network) as the default router. Then all should be ok (assuming that the router is configured ok - so netstat -nr would tell us that). Kevin.