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Moving a subnet from router to router, one address at a time

Please bear with me as I have only been administrating cisco devices for about 2 months.

I got handed this project when our net admin was fired.

My company has two datacenters. At our new datacenet (DC-A) we have a cisco 3845 and at our old datacenter (DC-B) we have a cisco 3662. DC-A has a subnet of lets say and DC-B has a subnet of I need to move from the DC-B to DC-A without lossing the IP address. At first I thought about doing an "ip nat outside source static" but that will not work becuase the interface connecting the two routers has the statement of "ip nat inside" already on it. This is becuase of an interface at DC-B that is connecting to a third party and we need to NAT the addresses.

Does anyone have an idea how to accomplish this task?

I would like NAT the addresses as we would like get rid of the subnet altogether over time. I am open to other idea though.



Patrick Laidlaw


Are you just moving the the device or do you need to move the actual IP while leaving still at DC-B?

It also helps to have your router configs available, and if you could do a quick visio of the network setup and what you want to accomplish we can come up with a configuration for you.


I am moving the physical computer and the ip address. I need to leave the 172.17.0/26 subnet at DC-B.

I will try to get the visio diagrams and configs posted.


you could do this by having in two places at once.

Configure it in the new location. DON'T advertise it into your network. Your network should see in its normal place.

As you move each machine add a host specific route for the machine you are moving to a suitable point in the network and redistribute if necessary.

Its going to get messy very quickly if you are talking about a large number of devices, but if its lots of servers I imagine you are using fixed addresses which would mean a manual reconfiguration of every single one if you were to use a new network.

Its a nasty "hack" but it would work.

I gave up on the NAT idea and I think this is what I have been trying to do. I have setup a test lab with two 2600 series routers to work through the details.

I can get the network configured on both networks. One router has as it's primary IP address on the Ethernet interface and one router has as a secondary IP address on it's ethernet interface. But routing isn't working as I had planned. EIGRP keeps getting in the way. I thought static routes had higher precidence over EIGRP but I must be doing something wrong.

How do you configure a subner but not advertise it? Is there a way to exclude addresses(or subnets) from EIGRP?



Have you thought about Local Area Mobility?

It's very easy to configure and supported by EIGRP.

The interface that has mobile hosts on it has to be enebled with ip proxy arp.