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Adding DHCP Scope

Posted on 2013-05-12
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Last Modified: 2013-05-15
I have one DHCP server in a small network. I have used all the IP addresses in the subnet. 10.10.1.0/24
I want to add few computers and put them in 10.10.2.0/24. so far I have one scope on DHCP 10.10.1.0/24
DHCP server IP address is 10.10.1.11,


how can I do that ? do I have to buy a router and a switch, for instance cisco router and a cisco switch ?
in My network, I have a non manageable switch connected to DSL router
I have heard about DHCP Superscope, but I am not sure if this will work since DHCP server has only on Network Adapter.

Thanks
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Question by:jskfan
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16 Comments
 
LVL 7

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by:eerwalters
eerwalters earned 100 total points
ID: 39160309
You could just change the subnet mask to make the scope a /23 for 510 addresses or a /22 to get 1022 total available addresses, depending on how many you need.

See the following link on how to change the subnet mask.  

http://www.windowstricks.in/2009/06/how-to-change-subnet-mask-of-dhcp-scope.html
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LVL 10

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by:Pramod Ubhe
Pramod Ubhe earned 50 total points
ID: 39160829
You just have to create a new scope 10.10.2.0/24. and activate it. As long as your network devices are configured to use this VLAN, it should work fine.
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LVL 8

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by:teomcam
teomcam earned 50 total points
ID: 39160839
I believe you are torturing your poor DSL router. You better to buy a router and start using it. You need to create another Vlan on your router then create a new scope on DHCP.
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Author Comment

by:jskfan
ID: 39161072
eerwalters:

if you change the subnet to /23 or /22, you will still end up with different subnets I believe and you will still need a route.
=======
pramod_ubhe:

I have a non manageable switch ,just dumb switch. It means I will have to purchase manageable cisco switch to configure VLANs (Layer2 or Layer3)and cisco router.

==========


I guess another way is to add Network adapter to my DHCP server and configure RRAS on it. Add new scope 10.10.2.0/24.
I am not sure if I need to configure superscope ..
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Author Comment

by:jskfan
ID: 39161186
I have been reading the article in the link below, all it requires after creating superscope , is to add another IP subnet to your existing adapter. in TCP/IP configuration, click Advanced and add the second IP Address from the second subnet to your DHCP server  .
 
The article does not recommend to turn the DHCP server into a router, using RRAS.


http://www.techrepublic.com/article/create-a-superscope-to-solve-the-problem-of-dwindling-ip-addresses/6131003
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LVL 4

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by:iconnectu
iconnectu earned 150 total points
ID: 39161243
You don't have to buy another router or use VLANs or so. Just enlarge you Subnet to 23 (255.255.254.0) and change the DHCP Range from 10.10.1.100 to 10.10.2.254. This will solve your problem and don't create a second subnet.
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Author Comment

by:jskfan
ID: 39161377
iconnectu:

Your statement makes sense...
I am not sure why the article in the linked I posted above did not mentioned your approach as an option.
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LVL 16

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by:vivigatt
vivigatt earned 150 total points
ID: 39161449
Enlarging the subnet is certainly the way to go, especially if there is no architectural reason to differentiate the devices getting 10.10.1.x and the ones getting 10.10.2.x.
Note that 10.x.x.x is a private class A subnet and, usually, the subnet mask for it is 255.0.0.0.
If you want more than 254 computers (a typical private class C subnet, 192.168.x.x/24) you might have used 172.16.x.x (private B class... There are several of it).

Check :
https://en.wikipedia.org/wiki/Private_network
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Author Comment

by:jskfan
ID: 39161539
Ok after enlarging the subnet, for instance to /23. without a router , how would a computer in 10.10.1.x network be able to talk to a computer in 10.10.2.x
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LVL 16

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by:vivigatt
vivigatt earned 150 total points
ID: 39161602
They are then in the same subnet, so they don't need a router !
For instance, all computers in 10.x.x.x/255.0.0.0 are in teh same subnet and can talk to each other.
Check:
http://support.microsoft.com/kb/164015
http://en.wikipedia.org/wiki/Subnetwork

A TCP/IP host know it has to send a TCP/IP packet to a router if the recipient is not in its subnet. To determine that, it compares the subnet mask and the recipient address... When you have modified your subnet to, let's say, 10.10.0.0/255.255.0.0, all IP addresses starting with 10.10 are considered to be in the same subnet.
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LVL 4

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by:iconnectu
iconnectu earned 150 total points
ID: 39161644
Your Computer in the 1.xxx will get an IP Address like this:
IP: 10.10.1.233
Subnet: 255.255.254.0
Gateway 10.10.1.1
So the clients know, that there is something more, because of the Subnetmask. Clients in the .2.xxx will get something like this:
IP: 10.10.2.233
Subnet: 255.255.254.0
Gateway 10.10.1.1
They know, that they are in the same Subnet. Trust me, they will find each other.
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LVL 7

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by:eerwalters
eerwalters earned 100 total points
ID: 39161738
As iconnectu and I have stated, you only need to enlarge your current subnet.  Just be sure to reference the link that I previously posted for the backup/restore of the DHCP assignments while creating the new subnet.
  Otherwise, you will have to enable the conflict detection option on the DHCP server to avoid the newly created (enlarged) subnet from assigning addresses that are actively in use.

  I am assuming that a Windows server is serving as the DHCP server.  If not, what device is providing that functionality?
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Author Comment

by:jskfan
ID: 39162673
Thank you Guys!! so as long as the subnet mask is the same for the enlarged subnet, then it means that all hosts in that subnet can talk to each other.

10.10.1.1/23 can talk to 10.10.2.1/23........... I need to review the subnetting..
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LVL 16

Accepted Solution

by:
vivigatt earned 150 total points
ID: 39162789
Well, that's almost true, but the notation is somewhat confusing.
I guess that what you mean is
"host with address 10.10.1.1 with a subnet-mask of 23 bits can talk directly (without routing) to host with address 10.10.2.1 with a subnet-mask of 23 bits".
And this is... false!

If you use 10.10.1.0/23, the actual range for your IP addresses are:
10.10.0.1 - 10.10.1.254
Yes, you read correctly ! 10.10.0.1 is the first address of your subnet with 23 bits of mask. The actual notation for such a subnet would be 10.10.0.0/23
Check:
http://www.subnet-calculator.com
or
http://jodies.de/ipcalc

Note that 0 in the host portion of the IP address is perfectly valid for subnet masks below 24 (10.10.1.0 would then be a valid host address)

If you absolutely need to have 10.10.2.x, then you have to use another subnet mask:

with 22 bits of subnet mask, you could use 10.10.0.1 - 10.10.3.254

So you can use a subnet mask of 22 bits and create a DHCP scope in the range 10.10.1.1-10.10.2.255, keeping in mind that 10.10.0.1-255 would still be valid IP addresses in this subnet, and that the broadcast address would then be 10.10.3.255.
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LVL 4

Assisted Solution

by:iconnectu
iconnectu earned 150 total points
ID: 39163089
Sorry, my fault. vivigatt is totally right.

If you really want to use the 10.10.2.x scope, you have to use 22 Bit. Starting by 10.10.0.0 - 10.10.3.255.

If you can use the 10.10.0.x range, instead of 10.10.2.x, you can go with 23bit, or 10.10.0.1 - 10.10.1.255.
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Author Closing Comment

by:jskfan
ID: 39168887
thank you guys!
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