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Possible to run two DHCP scopes?

Posted on 2004-08-10
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Last Modified: 2010-04-13
I was wondering if I could get my win2k DHCP server to have two separate scopes.
One would be for 192.168.1.1-192.168.1.12

The other would be for 192.168.2.1.-192.168.2.12

I have my LAN segmented (2 cisco routers)

Would this work or am I crazy?  
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Question by:dissolved
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by:dlwyatt82
ID: 11769194
That is a perfectly normal configuration. You just need to make sure that your router is configured to forward BOOTP / DHCP packets to the IP address of your DHCP server.
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by:dlwyatt82
ID: 11769216
For further clarification - DHCP traffic is broadcast, and does not pass beyond the boundary of a physical segment (router) by design. Assuming your DHCP server is on the 192.168.1.0 segment, clients on the 192.168.2.0 segment can't receive addresses unless your router is configured to forward any BOOTP / DHCP packets from that subnet to the IP address of the DHCP server.

The router, before forwarding packets on to the DHCP server, identifies its IP address in a "gateway" field, so the DHCP server knows which IP subnet the request is coming from. It checks to see if you have a scope defined that matches the appropriate IP range, and if you do have a properly activated scope, picks an address from that pool.
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by:dissolved
ID: 11769256
Thanks man.
2 more questions.

1. what ports need to be forwarded on my routers?

2. Will the clients on the 192.168.2.0 network, automatically receive a 192.168.2. address from the DNS server?
Thanks
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by:dgroscost
ID: 11769263
Are you going to use a DHCP Relay Agent (Win2003) for your other location?  
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by:dissolved
ID: 11769274
I didnt plan to. But after doing some research, it looks like I will need a DHCP relay agent because I have a segmented lan (192.168.1.0 and 192.168.2.0).
Am I correct?
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by:dlwyatt82
ID: 11769280
1. You don't need to know the specific port numbers, there should be an option explicitly named "BOOTP forwarding" or "DHCP forwarding". It is a standard option on current routers. I don't remember the UDP port numbers off the top of my head, but you can find them with a quick google search if you're curious :)

2. As long as you have already configured and activated a scope for the 192.168.2. subnet on your DHCP server, then yes. Any client who has a DHCP request forwarded from the 192.168.2. subnet will receive an IP address from that scope.
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by:dlwyatt82
ID: 11769285
dissolved - if your router supports BOOTP forwarding, then you don't need to use a Windows server with the DHCP Relay Agent. I honestly don't know why Microsoft highlights this option so frequently, which virtually all current routers on the market support forwarding of BOOTP / DHCP packets.
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by:dlwyatt82
ID: 11769299
For more information regarding DHCP and how the relay agents (whether on a router or a Windows machine) work, check out this link: http://www.microsoft.com/resources/documentation/WindowsServ/2003/standard/proddocs/en-us/sag_DHCP_und_RelayAgentNode.asp

This is from the 2003 documentation, but the information is accurate for 2000 as well.
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Author Comment

by:dissolved
ID: 11769304
Thanks guys. Now I have to find out how to activate DHCP forwarding on my cisco router (cisco newb here)

Thanks again
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by:magus123
ID: 11769962
if your using windows 2000 server . all answers above are correct .
you should also consider using the superscope feature in dhcp .
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by:dlwyatt82
ID: 11771563
Magus, configuring superscopes in this situation is not really appropriate. They are used to group together multiple scopes into a single logical scope when several logical IP network addresses are being used on the same physical subnet. In dissolved's network, there are two physical subnets, each with a single logical IP subnet.

If he were to create 2 superscopes, one each containing only one scope, nothing interesting would happen. It wouldn't break anything, but nothing would be gained, either.
If he created a single superscope containing both scopes, the system would begin handing out the wrong addresses to random clients on one or both subnets.
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by:dlwyatt82
ID: 11771591
Note - my last comment refers to the way DHCP superscopes work in Windows Server 2003. I don't remember for sure if this was the way it worked in Windows 2000 DHCP.
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by:dlwyatt82
ID: 11771623
Just double checked - the implementation of superscopes is the same for Windows 2000. See http://www.microsoft.com/resources/documentation/windows/2000/server/reskit/en-us/tcpip/part2/tcpch04.mspx
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by:magus123
ID: 11773266
dlwyatt82 ,
i am goin to have to look more into that , my understanding of scopes must be a little off , the basics
are their , but the way they are applied ill hve to see. thanks.
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by:magus123
ID: 11773369
after some resarch your conslusion

1. scope = creation of  1 scope/range  per subnet.
2. superscope = multiple ranges for only 1 subnet.

is this correct  scopes can give you ranges but are only applicable to 1 subnet.
thanks for any info , i appreciate your help , as i studying this stuff right now.
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Accepted Solution

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dlwyatt82 earned 50 total points
ID: 11773835
That's essentialy correct, magus. It helps to specify "physical" or "logical" in the explanation, as the word "subnet" is used to refer to both:

A Scope is a range of DHCP addresses in one Logical subnet.
A superscope is a collection of Scopes (Logical subnets) which all apply to one Physical subnet.

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