DHCP Server

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I haven't contributed to this thread before because my DHCP knoweldge isn't what it should be.

However, from my (limited) experience, there isn't an option to assign a specific DHCP server to different subnets in the Scope options. You may be able to create a custom scope option to achieve this, but I'm not sure how to go about doing it.

There are some IP address management programs and appliances around that would probably take care of this for you - but they're not free, and are definitely not going to be relevant to answers for an MS exam!

As far as my understanding goes, you just cannot get addresses for a remote subnet served by DHCP without installing a relay agent on the router that sits between them

 

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if memory serves me correctly you can't do this without multiple nics. Even if you could, you'd end up with pcs unable to communicate with each other unless you had a router, and multiple IP's assigned to a single nic on the dhcp server. Nope, as has been said, multiple nic's is the way to go. Class IDs are used to differentiate types of h/w or o/s - not to differentiate scopes.

hope that helps. I know I could be clearer but it's late and I'm needed elsewhere...

 

Wow! What a thread! Very informative!

I've been trying to follow this thread when I've had the time but its bloody hard when you're not at work!

I can agree with what has been said about a router being needed to route between the subnets, but those of you who have access to the diagram on which the original question is based should see that the DHCP clients seem to be on the same segment of the network, before the router, yet they have IP's from different subnets. Surely, by default, therefore they would be able to see the DHCP server before going anywhere near the router???

Simon. (out of touch as he's still on hoilday!)

 

The example in question refers to a proper router requiring a bootp or forwarder per subnet - it is a standard type of cert question based on a common scenario.

Alternatively - and in real life -if you set up the server with two NIC's and set up the static routes correctly it will all work in the absence of a router.

Basically you create separate DHCP server instances running on the server for each interface which functions as the [admittedly poor] router between the subnets...

HTH

supa

 

to be honest im more confused now than when i started this thread.

Can what i have described be done? I mean its clear in the MS Press book so surely it can be done. I cant show the pic in question here on the forum because of copyright issues so please could you find the pages somewhere further up. Microsoft are always going on about a DHCP Server giving out IP's to several subnets so how does this blimy DHCP decide which IP's go where?? Im not saying i wont use a router if i need to so be it! So how we going to go about this?

Edit: not sure if anyone has seen Sparky's explaination - sorry i havent tried it yet cause im struck down with flu!

 

not with IP they can't ! unless the server has multiple IPs per nic. Still needs a router installed on the server though (or elsewhere) to allow communication between the scopes...

 

well, I don't have the book, but it seems to me that you'd be looking at superscopes here...

have a look at this article
http://support.microsoft.com/kb/161571

 

i have tried superscopes before... you have 2 scopes and 2 different clients (so one client will get an IP from one range and the other client from the other). BUT BOTH clients end up getting IP's from the first subnet! So there is the problem! How do you define which IP's go to which clients?

 

afaik you don't - the first scope gets used up, then the second.

 

Hi Zimbo

Sorry to harp on with the same point, but how have you set up your multinet? How have you distinguished between segments and therefore assigned the clients to different subnets?
When you put static ips on each client(from the ranges you would like them to take?), can they communicate to one another and to the dhcp server?

Generally setting up dhcp isnt too tricky, it only becomes so if your dns and your routing is not up to it. Multinets are logical subnets, they still need routing and default gateways. The book doesnt make that clear, but it does say it.

If you dont believe me( and that would hurt my feelings! ) google dhcp packets, see how they are formed, then look at what the routers add to them when they need to be routed to a dhcp server in another subnet to inform the router which scope the address should be issued from.
What you are trying to do is basically the same thing. Your dhcp server needs to know which subnet(multinet) the request is coming from.

The book makes it clear it expects you to use a router and set up the network segment properly first before you start trying to use dhcp.

You'll also find this is the process you have to go through when you're troubleshooting in the real world. Most apparantly dhcp problems turn out to be dns. And by the time you work it out you're body has more more caffeine than blood!

 

Thanks for the input! So it cant be done?

 

You may well be looking at an IPAM appliance.

For various reasons (mainly accountability) we use static IP addressing across our entire organisation (200 sites!) but were recently considering a move to DHCP. This was subsequently shelved due to budget and the aforementioned accountability issues, but we were looking at these guys when we were scoping (pardon the oun) it out.

Cricket Liu (who, for those not sad enough to own a copy) literally wrote the book on Windows 2K3 DNS is their VP - and authorities don't come more 'authoritative' than that!

That said, I realise its probably not going to be the answer for an MS exam question...

 

YES!!! It can be done. just set up the router!!! just like in the diagram they give you. set that up right, and it will work immediately

 

ok what you mean setup the router? How about I setup RRAS?

 

I don't know if what I am about to say is going to be any good to you zimbo but I have tried setting the same thing in vmware and it does not work.

 

If wanting to get DHCP server information over from one subnet to another then you will probably need to set up a Relay agent for passing TCP/IP configuration on to another subnet, why do you need two subnets in the first place, when going for network+, the only question(s) you will get on the exam are, when you would need to subnet a network, and understand why subnets actualy exsist, sounds like you are mixing CCNA into this.

 

dont know anything about vmware(thats my next project!) so I dont know how you go about setting up a router on there. you may be able to do it with the rras, setting it up for lan routing, but i've not tried that before.

when i did that course i was lucky enough to be able to do it with physical boxes and a cisco router, and there were no problems so the lab is definitely do-able.

Sorry, im a total pleb with virtual stuff, but the key to the lab is setting up a router, if you cant do that then just leave it, you wont be able to make it work as the book intends otherwise, and that particular lab wont affect your understanding of dhcp too much either way.

The only point being made there is that you can treat multinets in the same manner as subnets as far as dhcp is concerned.
THe dhcp server issues addresses based on the information in the discover packet. If you get that then you're fine, move on, there's nothing else to see here!

 

and i agree with sparkys last post!!