IP Routing Between Subnets 1

[lbarron]

Hi,

We currently have two subnets on our network as we are in the process of moving to Windows Server 2K3.

All our new machines in the AD are set to use the 192.168.0.x range, and all old machines not yet migrated are using the 192.0.3.x range. Currently our mail server sits on the 192.0.3.x range and we are giving all the new machines dual ip addresses.

What we would like to do is change the address of the mail server to the 192.168.0.x range and do some kind of routing so that all machines in the old range can still access the server.

I'm not sure about the best way of doing this, either installing a second NIC or buying a router?

Any help would be appreciated.

Thanks

Lee

 

[pgaliardo]

Probably the easiest and correct way to do this is to implement a router. Then create a route to connect the 2 subnets.

You probably could get around it wuth adding a second NIC to the mail server. Assign that NIC an address in the 192.0.3.x network. Have all clients and the second nic on the second mail server cabled into the same switch. They will all see each other by IP Address, but I am not sure if they will see each other by name. In that case you may have to implement a DNS or WINS server on that segment or statically add host names to each machine with a hosts file.

 

[kbing]

VLANning sounds like the solution to your problem. The layer 3 switches would be more efficient at keeping the subnets separated while you migrate users over to the new IP scheme. You don't need to dual-IP each machine if you do this.

 

[pgaliardo]

Good post kbing. You're right, this situaution is perfect for a VLAN, and a layer 3 switch would provide routing between VLANS.

 

[lbarron]

Hi,

Thanks for all your posts.

I am not that familiar with VLANing so I will have to do a bit of reading up, can you point me in the direction of some good reasding aterial?

All our servers are connected into a HP Procurve 5304xl switch which I think supports VLANing.

I assume I only need to configure the VLAN on this switch as we don't have managed switches across the whole sight.

Thanks

Lee

 

[pgaliardo]

Lee,

A VLAN literally means virtual LAN. It is really not that hard to understand. Probably your best source for reading material is with the HP Documentation itself.

From what I can gather about your switch, it looks like it does support VLANS and Layer 3 switching, you may already have everything you need.

You only need to confiure the VLAN on this switch if all devices on both VLANS connect to this switch. If there are devices interspersed throughout the network that need to belong to the VLAN, then it gets a little more complicated.
For example, if Device A and Device B both belong to VLAN1 and Device A is plugged into the 5304, and Device B is plugged into another switch, then that other switch will also need to support VLANS and have to be configured.

Hope this all makes sense.

 

[LawnBoy]

The HP 5304 is a good machine, I have 2 5308s. It is wildly capable of VLANs (it can do 256 of them iirc). It will not route between VLANs, you would need an external router to do so. HP's website has excellent documentation, you'll be startled to find out all that switch can do.

I have never heard of a switch routing between VLANs, except for IPhelpers passing DHCP across multiple VLANs. But that's a whole other kettle of fish.

 

[LawnBoy]

Heh, in answer to your OP, I would install a second NIC in that server and set it up on the other subnet. It is by far the easiest and cheapest answer.

 

[Kwazzy]

My first question is why do you need two subnets. If you are that small of an office, is it really helping you to have muliple subnets?

Now, if you are trying to limit broadcasts between devices, that is some what understandable. If you must persue the two subnets and you would like to make sure you have a managable solution going forward for the company's prospective. I would go with the router or layer three switch.

Basic view of VLANing:

Layer three Vlans allow you to take a 24 port switch(most common) and segment the switch to each individual port. So you can selectivly choose what port is what Subnet (if you make your vlans = to subnets). (Which most companies do.) Example - You can choose Sally, Mark and Joe to be in vlan 1, and your file server printer, and print server on another. All connected to the same switch. Just that you have broken up certian ports for different VLANs.

Dual nics are ok if you need to do this with the cheapiest solution possible. But this is not a clean network design and not a practical setup.

 

[kbing]

I think we should get back to the issue at hand. In order to solve your problem, you will either need a router to route from 1 subnet to the other...or you can buy a layer 3 switch to route from one subnet to the other.

Layer 3 is the routing aspect so switches can accomplish this. If you want to go cheap - try Dell 5324. They work great. I have 20 of them in my network and they work very well for the cost ~$800.00

I would stay away from dual-IP addresses on any machine. It's not worth the effort. I'd rather spend my time installing the router of L3 switch.

 

[lbarron]

Thanks for all your posts.

I have installed a second NIC in the mail server to solve the problem quickly and cheaply. As we are moving towards a single subnet we didn't want to spend a lot of money on a solution.

Thanks guys for all your help.

Cheers

Lee