New LAN Implementation on to existing network

[muhammedt]

Hey Guys,

I kinda got stuck in a network mess at my new job. To give you some background info: Our dept is a sub dept of huge company. And our network was originally desgined to be a flat L2 network. Someway along the line some crafty network guru introduced VOIP and other private networks on the existing network. Now our situation is we are implementing a new private lan 10.15.100.0/22 to the existing public lan 170.115.38.0 /23 network because we are running out of ip addresses. Our core router 170.115.38.1 is in another building and we cannot manage it. The network architect at our company's NOC gave us an "overlaid" network on the existing network to migrate to. 

The core switches have had an ip address given on the new subnet and to get the subnet working there has been a route made on our firewall for the new subnet to route through the ip address of 170.115.38.4. This is causing multiple connectivity issues to servers that have their default gateway set to 170.115.38.2. You can ping them, but you have issues connecting to websites our internal servers host and other bizarre issues. Not to mention congestion. Also having two subnets on the default VLAN creates two broadcasts. What are some solutions I could implement?

I am attaching a visio diagram I quickly made that explains what I'm dealing with. I can provide switch configs if necessary. 

[Philip D'Ath]

Do you have any down days, like a Saturday or Sunday?  If so, I would be tempted to go for a "big bang" and just cut across to the new ranges in one big hit.

I see you have all HP switches are you are asking questions on a Cisco forum ...

You should have your default gateways set to point to the core switch, and it should have both old and new IP addresses loaded on it, and everything should be able to talk to everything else.

[muhammedt]

I have thought of that. But think of our dept as a separate company. Because we have a lot of app servers and internal servers that need their network settings changed. Nothing is documented so I'm not sure if changing the settings on these app servers might break the app. Plus I have to make sure everything is working. I dont want to move everything over at once and something doesn't work. I was hoping for a smoother transition. Otherwise things could go wrong very quickly. 

Also yea, we have other cisco devices but the core is those hp switches. Just gotta roll with it.