Changing IP ranges but keeping server on both?

We have a site where we're being forced to change the IP range, problem is that the way some of the legacy software works it'll require to still see the server on it's old IP address.

What I was wondering was, if it'd be possible to have the server having two IP addresses and simply get the clients to resolve both back to the same server?

I'm just trying to think of solutions to it, it's a few months off still :) I have a feeling that'd work, but with the clients on the new range, they should still resolve back to the old IP address if we manually set it in LMHOST surely? Or even as long as there's an entry in DNS as long as we had the switches setup correctly.

Correct me if I'm wrong please folks, it's been a bloomin long day! :D

Um, yea it would work but it would be a hack. You could have the server setup to keep both ip addresses but the clients would need to be on only the new addresses under DHCP so to talk to the server with the old IP address the traffic would need to be routed by the default gateway back to the server in question. This causes a bottleneck as all traffic must pass through the router to end up at the server even though it is locally connected.

The LMHOSTS file work the other way pointing a distinct name to an ip but if your apps are configured with the ip directly this will not help unfourtunatly. If they were configured with a name instead it would be easier just to use an A record in DNS.

How solidly locked are these programs in to the ip addresses, would it be possible to reconfigure them all by applying a large registry patch / config files updates to all hosts as this would probably be a better solution long and short term. It would take a little initial research into how the config is stored with the apps but then your not opening yourself up for the possible hazzards of unconventional routing in future.

I'd much rather just change the IP in the apps to the new one but it's timescales, has to happen within 3 days and that's from a bare building to a fully working 80 office, 3 story building with 3 domains and 45 PCs/domain. The building won't even have any network hardware in, that'll all have to be done by us too.

Of course we only have 3 staff to do it with..

However I know what you're saying and unfortunately changing this hack later won't be any easier than doing it correctly now, so I'm in two minds!:D

The apps themselves are custom and although I could get the company in to alter them I know for a fact they'll mess it up and then leave us to fix it. I think that might be the only way to get things up and running in time though.

Cheers Synack - dont' know why I was thinking of using lmhosts, completely around the wrong way - I know how it worked, just got myself confused. That's the problem with starting at 5am! ;)

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Originally Posted by SYNACK

This causes a bottleneck as all traffic must pass through the router to end up at the server even though it is locally connected.

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I'm not sure this is true. Most routers would send an ICMP Redirect packet to the source telling it to update its routing table and send subsequent packets directly to the destination MAC address since they're on the same segment (same router interface).

I haven't encountered this behaviour directly but it may be that way, I think it would depend largely on the router though as it is a rather non-standard setup.