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Win2003 DHCP. How does having multiple scopes work?

Posted on 2006-05-08
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Last Modified: 2013-12-23
Hi,

I am new to DHCP. I have a network which is 192.168.0.x range (so only supports 254 machines) and we have about 270 machines :) Thankfully they have not always all been on at once, however lately we are running into troubles.

I was wondering what the easiest way to assign more ip's. Can I just add an additional scope in DHCP say for 192.168.1.x range? Then when the first scope runs out, it will start allowing people to retrieve IP's from this second scope?

The 2003 Server I have has 2 network cards, both connected to the same physical network.

Any ideas would be great... or perhaps something completely different :)

Cheers,

Paul.
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Question by:H4Inf
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LVL 32

Expert Comment

by:r-k
ID: 16636894
You should try this:

Change the "End IP Address" for your scope to 192.168.1.254 (instead of 192.168.0.254)
The subnet mask should be 255.255.254.0
Everything else should stay the same.

As far as I know this should double the IP's available.
I am not a dhcp expert but it's worth a try.
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by:H4Inf
ID: 16636924
Hmm it says it overlaps an existing range or is not valid.
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Expert Comment

by:r-k
ID: 16636938
You may need to change the subnet mask for your system to 255.255.254.0
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by:r-k
ID: 16636946
Sorry, cancel that last comment.
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r-k earned 1600 total points
ID: 16636978
I think you will have to create a new scope, going from 192.168.0.1 to 192.168.1.254 (if that is the range you want) and specify the subnet mask as 255.255.254.0 (instead os 255.255.255.0)
For Gateway/DNS etc. use same settings as before.

You will need to delete the old scope before doing the above, so make careful note of all the settings such as lease duration etc. in case you have to restore it.
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by:bbao
ID: 16643857
hi H4Inf,

what r-k means is to expand your current DHCP scope from 253 (not 254, because you commonly need to reserve at least another IP for router and/or DHCP server) to a bigger one by adjusting the subnet's mask from 255.255.255.0 to 255.255.254.0 (one higher bit used, which means you may have up to 512 - 3 = 509 DHCP clients).

so please remove the current DHCP scope, create another new one, with the expanded scope specified, just as what r-k mentioned above.

hope it helps,
bbao
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Author Comment

by:H4Inf
ID: 16644476
Hi Guys,

Thanks so far,

I have about 40 servers with statically assigned IP's. This means that I will need to change all of their subnet masks to 255.255.254.0 correct?

And this will then give me a usable range 192.168.0.1 - 192.168.1.254 correct?

Cheers,

Paul.
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Assisted Solution

by:bbao
bbao earned 400 total points
ID: 16645901
> I have about 40 servers with statically assigned IP's

if all the clients possibly need to talk with all the servers, i suppose that you have two approaches may be considered:

1. a labor intensive job, to manually change the server's IPs. it is recommended if you prefer to keep only one subnet. actually, it is also the thorough solution.

2. setup a DHCP-relay enabled router to interconnect the 0.x and 1.x subnets and relay DHCP packages across the two subnets. all the existing servers are still located on the 0.x subnet.

if most clients do not access the internal server, e.g. only to access the internet. then do nothing on the existing servers. keep the few clients which need to talk with the servers in the 0.x subnet.

hope it helps,
bbao
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Expert Comment

by:jonoakley
ID: 16649275
Or add the MAC of each server to the DHCP scope, and never worry about making massive changes to local static IPs
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Author Comment

by:H4Inf
ID: 16657588
Excellent I think I have a plan then.

I will keep the servers statically assigned, in the case that the DHCP server goes down and then the power goes off and comes back... all our servers will be offline! That would not be good.

I am thinking of using perhaps a 255.255.252.0 subnet mask.

This should give me 192.168.0.1 -> 192.168.3.254 = 1022 ip addresses, right?

Then we should never ever run out of IP's again :)

I will try to implement this about 20 hrs from now.
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Author Comment

by:H4Inf
ID: 16829818
I noted down all the reservation details and setup a new scope 255.255.252.0 so I have ~1022 addresses.

All is working well :-)

Cheers,

Paul.
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Expert Comment

by:r-k
ID: 16830380
Thanks. Great to know its working.
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