Best way to change LAN IP Addressing

Posted on 2011-10-26
Last Modified: 2012-05-12
Hi all

I inherited a network a number of years ago that consists of various firewalls, switches, printers, PC’s, servers, etc, etc (the usual stuff) on it. Most of the IP addressing is handled by DHCP servers, however there are some items, like printers, switches and servers that have static IP addresses (there are exclusions for these in the DHCP setup to prevent duplicate addresses). The whole LAN is on the one /24 subnet.

The issue I have is that the IP addresses assigned, when the network was set up, are actually public IP addresses that I don’t own, so when you do a reverse DNS lookup on a local IP address you get name of a machine on the WAN that isn’t one of mine.

Does anyone have any advice on the best way to change the IP addresses in use to a proper LAN IP to minimise downtime or would you have any suggestions on how I can fix the RDNS issue?

Many thanks in advance
Question by:LukeFileWalker
    LVL 17

    Accepted Solution

    Obviously, changing to some RFC-network (192.168, 10, 172.16-31) is the best thing to do. As for minimizing downtime - make a list of statically configured devices, sort by importance, then move the DHCP server over to the new network addresses and work from there. In a pinch, you could also set up a router with dual IP addresses, one in the new, one in the old range, and let it route between the ranges, allowing the dynamically assigned boxes still reach the old addresses while you work through the devices. Though I personally would want to avoid this ...
    Also, during preparations, make sure you know whether there are any applications using the IPs instead of symbolic names. These would also need to be fixed ...

    Author Closing Comment

    Apologies for the delay in getting back to you
    Many thanks for the advice

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