Subnet Question

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Hi everyone,

I have a hopefully easy questions about subnets. Basically, if I have a single domain at one physical location using Server 2003 as a DC, how do the IP addresses of each subnet get assigned, and how do I designate how each subnet gets its IP address? Can anyone give a physical/logical example of how it's done?


thanks!

 

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do you mean which parts of the domain get what IP address and who determines them?

 

yeah, exactly that.

 

well the system administrator determines them. Its a process called subnetting - where you take your large network and split it into smaller more manageable networks. What determines what is the subnet mask. I think if you want more info and i think you should since you going for MCSA is google 'subnetting' or search here because there is a few threads on subnetting!

 

Old favourite around here:

Learn To Subnet

hth

 

Like Zimbo says, google Subnetting and you will find the answers.

What you have to think about is how you want the network to communicate. Is it a large network, where there are specific devices that link other parts of the network, or one where you simply want everything to be on the same subnet and talk to each other.

 

i forgot about that and i even got the cd!

 

Well I think you can explain roughly what happens even if you are not fully conversant with calculating the subnetting information.

Lets just look at two common private IP ranges. 192.168.0.0 and 10.0.0.0

You use routers to separate subnets, so for this example I will stick two NICs in a Windows server and set up RRAS (routing).

I then configure one NIC with a static IP of 192.168.0.1 and the other with a static IP of 10.0.0.1

Then in DHCP on the server, I set up two scopes. One for the 10.0.0.0 subnet, with a pool of IP addresses that allows sufficient for the number of clients I have, say 10.0.0.2 to 10.0.0.100 and do the same for the 192.168.0.0 scope.

The DHCP server is clever enough to realise that a DHCP discovery (request for IP addy) coming via the 10.0.0.1 NIC, will need an available address in that range and the same is true for the other scope.

It gets more complicated if a DHCP server does not reside on the actual subnet, that's where relay agents come into play.

HTH

 

Thanks Bluerinse, that was actually the answer I was looking for. I understand the principles of creating the actual IP subnet, but I wasn't sure how it was actualyl deployed in a network... I didn't realise that the Server did it by NIC. So the routers that seperate each subnet run as DHCP relays...?? I'm just curious about the physical and logical setup once I have determied the IP addresses once I calculate the subnet

thanks!

 

not necessarily. unless they are configured to forward dhcp broadcasts, but i think many don't.
which is why you can configure an rras server on the local subnet to forward dhcp broadcasts to a specified dhcp server on a different subnet.

 

No, a DHCP relay agent is a separate device (according to Microsoft but they do exist in some multi-function routers) which has to reside on a subnet if there isn't a DHCP server. It relays DHCP packets to the subnet where the DHCP server is.

 

actually there's the helper s/w on cisco routers that does exactly that. It seems to me that having the local router interface act as the relay makes perfect sense, as otherwise you'll need a w2k server and if you do that you may as well install dhcp in it anyhow!

 

LOL true I suppose, unless you wanted to manage your scopes from one central DHCP server

 

er.. but with relays thats exactly what you'd do !

 

yes, but not when you deploy a windows box to relay and then decide you might as well host dhcp on it as you suggested, which is what bluerinse is getting at, i think.

 

oh yeah...

*lol* I'm thinking router, he's thinking server

ah well...

 

Yup, I was just trying to keep the discussion on topic, as the OP is studying for his MCSA