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I've got two servers with 3 interfaces between them all on the same VLAN.

Server 1: 1 NIC, 1 IP block (/29) with subnet 255.255.255.248

Server 2: 2 NICs, 2 IP blocks (one /28 and the other /29) with different gateways and different subnets. The subnet for the /29 block is 255.255.255.248, and the other one is 255.255.255.240. Currently, I have two IP blocks and two gateways added on NIC1 (of Server 2).

So, say I want to move an IP from NIC1 to NIC2 on the same server - Server 2. Do I need to have the gateway corresponding to that IP added on both NICs since I will have IPs from the same block on both interfaces?

Now, if I want to move an IP between two different servers, do I also need to add the corresponding gateways?

Basically what I want to accomplish is this:

Server 1: original /29 block will stay here, additional IPs from Server 2 from the /28 block Server 2: NIC1 - /28 block, NIC2 - original /29 block

Is this a logical and problem free setup? If I have two different gateways on two different interfaces on the same machine, I get the following error:

Warning: Multiple default gateways are intended to provide redundancy to a single network (such as an intranet or the Internet). They will not function properly when the gateways are on two separate, disjoint networks (such as one on your intranet and one on the Internet). Do you want to save this configuration?

All interfaces require internet connectivity.

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We probably need a lot more information about your addressing/subnets/routing on your network. Right now your question is pretty vague. –  Zoredache Feb 4 '11 at 19:25
    
I'll add more information. –  Radu Feb 4 '11 at 19:29
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1 Answer

The reason for the warning is that if you have multiple ips configured, say, 192.168.1.10 and 192.168.99.10 and two routers on this network (192.168.1.1 and 192.168.99.1) then all responses will go out over one of the routers until it fails to respond (arp doesn't resolve).

It won't balance the traffic over the two.

This will also have a side effect that connections coming in on the 192.168.1.1 router (say with a public ip of 123.123.1.1) will go out on the 192.168.99.1 router (say with a public ip of 123.123.99.1) so someone connecting to 123.123.1.1 will get a response from 123.123.99.1 .... i.e it won't work.

You need a more intelligent firewall/router to do this sort of thing.

How you move ip's between the server is probably not important if you are trying to achieve redundancy. You have a networking issue which windows is not really equipped to resolve and it would be better not to try. Inbound and outbound load balancing/redundancy networking equipment is not really expensive until you get to high end and it will cost you less in time.

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