How to configure split-scope using wizard
Split-scope configuration (Widely known as 80/20 Configurations) is typically considered as high-availability deployment scenario for the DHCP Server. It involves configuring scopes with the same subnet address and subnet mask and configuration on two distinct DHCP Servers. The two scopes have complementary exclusion ranges and therefore will not serve the same address to different clients.
The ratio of address ranges across the servers is denoted as Primary Server to lease 80 percent of the addresses in the scope and the secondary server to lease out 20 percent of the addresses in the scope. Splitting a scope between servers in this way, which is commonly referred to as the "80/20 rule," often relies on the proximity of the DHCP servers to the clients it serves. To avoid address range exhaustion on the secondary (20% address range) server, it can be configured to send out the DHCP OFFER with a small delay as well.
Configuration Steps:
Fig1- Launch DHCP server
Fig 2: Launch the Split scope screen
Right click on the scope that is to be split and press the advanced menu item and split scope menu item.
Fig 3: Initialization screen
Press the next button on this screen to proceed.
Fig 4: Add Secondary DHCP server screen
Add the secondary server in the edit box, if secondary server does not exist an error is displayed. It is only after having provided valid secondary DHCP Server one can click Next. Press next button to proceed.
Fig 5: Split scope configuration screen
Adjust the split using the slider control; all other values are automatically adjusted OR the split can be configured with percentage field or IP Address range of the exclusion. Press next button to proceed.
Fig 6: Split scope delay configuration screen
Specify the delay on the secondary server, press next button to proceed.
Fig 7: Configuration summary screen
This screen shows the selected configuration before you could proceed for split. Press next button after checking your configuration.
Fig 8: Summary results screen
Show the result of the split.
Fig 9: DHCP server showing split scope
This page shows the scope getting configured on the secondary server and the exclusion range set on the secondary server
Hope this helps you in configuring the Split-Scope and manage the address effectively. Suggestions, comments and quries are welcome.
Thanks,
TeamDHCP
Comments
Anonymous
January 01, 2003
Basically what needs to be synced is the configuration and the leases are never synced. So if you make new configurations on one server , you can create a netsh script of the configurations done on that server and apply it to the other server. -TusharAnonymous
January 01, 2003
It isn't possible to configure split-scope without UI. Thanks, Arun Dhcp TeamAnonymous
January 01, 2003
The exclusion ranges should be : DHCP1(host) address range 10.0.0.1 - 10.0.0.200 exclusion 10.0.0.121 -10.0.0.200 DHCP2(split scope) address range 10.0.0.1 - 10.0.0.200 exclusion 10.0.0.1 - 10.0.0.120 There should be no exclusion 10.0.0.121 - 10.0.0.200 on the second server. Wil correct the diagram. -TusharAnonymous
January 01, 2003
Please verify if there are vendor specific options configured for the scope which are not created on the secondary server .Anonymous
January 01, 2003
When you are using the split sciope feature , do you already have any existing exclusions on the scope for which you are trying to do split scope? Those exclusions too would be migrated . -TusharAnonymous
January 01, 2003
The exlusion ranges are on different dhcp servers. So an exclusion 20.0.0.1 20.0.0.80 is configured on the second server so that it does not give addresses from this range and only the primary (first) server services from the range 20.0.0.1 to 20.0.0.80. Similary exclusion 20.0.0.81 to 20.0.0.100 is configured on the primary so that it does not lease addresses from this range and only the second server leases addresses from the range 20.0.0.81 to 20.0.0.100 . -TusharAnonymous
January 01, 2003
When setup in a split scope configuration do Reservations/Options settings sync between the primary /secondary DHCP servers ? Subsequently when any changes are made on either servers are they synced between the primary and secondary DHCP servers?Anonymous
January 01, 2003
Hey Greg, This functionality is available only on Windows Server 2008 R2. Thanks Raunak PandyaAnonymous
January 01, 2003
Hi, I assume I have 100 users ,and the scope start from 10.0.0.1 to 10.0.0.100, and the scope split is done by 80/20 So DHCP1(host) address range 10.0.0.1 - 10.0.0.100 exclusion 10.0.0.81 -10.0.0.100 DHCP2(split scope) address range 10.0.0.1 - 10.0.0.100 exclusion 10.0.0.1 - 10.0.0.80 So my question, if the main DHCP server (DHCP1) is fails, Is it DHCP2 server can provide the full scope addresses range (10.0.0.1 - 10.0.0.100) ? OR it will only provide its dedicated range (10.0.0.81 - 10.0.0.100) and didn’t care about the rest of the range including 10.0.0.1 - 10.0.0.80 So DHCP2 in case of failure of DHCP1, it take care of full leased addresses ? or it responsible only for part of the scope ? as at this case there is 80 users still they didn’t got DHCP IP !Anonymous
January 01, 2003
That may be but I have set up the same setup on my Serv08 R2 DHCP servers. The same setup but with different IP ranges. The second DHCP server has the 2 exclusion ranges just like your example. When I stop the host DHCP server IP address handouts stop. The second DHCP server does not hand out anything as it is range excluded out of the scope. When I look at the host DHCP servers exclusions it only has the exclusions for the second DHCP servers range of IP's not 2 lots as the second server does. example DHCP1(host) address range 10.0.0.1 - 10.0.0.200 exclusion 10.0.0.121 -10.0.0.200 DHCP2(split scope) address range 10.0.0.1 - 10.0.0.200 exclusion 10.0.0.1 - 10.0.0.120 exclusion 10.0.0.121- 10.0.0.200 With this default setup as created by the Split Scope feature the second DHCP server does not hand out IP's when you stop the host DHCP. APIPA address are granted to hosts by themselves as they cannot get an answer from a working DHCP. Start the host and away it goes again. Delete the exclusion range on DHCP2 that corresponds with the host DHCP servers range and DHCP2 hands out addresses. If this is the correct way to set it up then I am missing something, can you please explain to me what I am doing wrong? Are we able to converse outside of this blog?Anonymous
January 01, 2003
thanks for the feedback. That is what I have done manually. So why does the DHCP Split Scope feature do this by default? I have created various Split Scopes to test with various IP ranges and all of them by default in the second DHCP server included 2 exclusion ranges, one to exclude the Hosts range and another to exclude its own range. Is this a bug as I have re-created the problem over and over. If using this Split Scope feature you manually have to delete the exclusion range on the second DHCP server for it to hand out IP's. Is this what is intended with the Split Scope feature as I cannot find any information on it at all. Please advise.........Anonymous
January 01, 2003
Ok Thanks. (1)Any plans on implementing this feature in the future? (2)If we need to manually sync do we backup the database and restore it on the secondary server on a regular basis using a script? Any info including a white paper on this?Anonymous
January 01, 2003
The comment has been removedAnonymous
January 01, 2003
During the first time setup of split scopes , the reservations and options do sync with secondary servers. However subsequent changes made do not sync and needs to be manually synced. -TusharAnonymous
February 05, 2009
Hi, great wizard, but wouldn't it be easier to store the dhcp database in Active Directory and have a second dhcp server to distribute the adresses - as failover.Anonymous
February 11, 2009
I don't see it mentioned in the article...which OS includes this functionality? Server 2008?Anonymous
November 14, 2009
Can you please explain why the second dhcp server has exclusion ranges of 20.0.0.1 to 20.0.0.80 and then a second exclusion of 20.0.0.81 to 20.0.0.100 out of its scope of 20.0.0.1 to 20.0.0.100. would not this render the dhcp server unable to hand out addresses? it has exclusion ranges that cover the whole scope. how can this be?Anonymous
May 12, 2010
when I configure a split scope, I try to go through the wizard and at the end I get an error. "Migration of Scope Options an Added DHCP server : Failed Error: 0x00004E2A - The specified option does not exist. My DHCP database was migrated from a previous win2003 machine. what should be the possible cause? unsupported DHCP option on R2? but the migration was successful, error only occur when i try to configure split scope.Anonymous
January 24, 2011
It is possible whitout wizard create or configure split scopes ? Because we have 60 scopes to split Best regardsAnonymous
April 27, 2011
What happen if the Primary server failed? The secondary server would not able to cover the 80% scope leased by Primary server. So I still need to manually delete the exclusion list in secondary server? Is 80/20 rule advisable on a Class C subnet with 80% ip usage? thanksAnonymous
May 17, 2011
Hi, I assume I have 100 users ,and the scope start from 10.0.0.1 to 10.0.0.100, and the scope split is done by 80/20 So DHCP1(host) address range 10.0.0.1 - 10.0.0.100 exclusion 10.0.0.81 -10.0.0.100 DHCP2(split scope) address range 10.0.0.1 - 10.0.0.100 exclusion 10.0.0.1 - 10.0.0.80 So my question, if the main DHCP server (DHCP1) is fails, Is it DHCP2 server can provide the full scope addresses range (10.0.0.1 - 10.0.0.100) ? OR it will only provide its dedicated range (10.0.0.81 - 10.0.0.100) and didn’t care about the rest of the range including 10.0.0.1 - 10.0.0.80 So DHCP2 in case of failure of DHCP1, it take care of full leased addresses ? or it responsible only for part of the scope ? as at this case there is 80 users still they didn’t got DHCP IP !Anonymous
January 22, 2013
i have split scope of 80 addresses to 80/20...how do I re-adjust to 70/30? How to get back the slider ? Do I need to remove the scope on one DHCP side first and redo it again using the wizard ?Anonymous
October 19, 2015
What changes would I have to make for the Split-Scope if I want to extend my DHCP Scope.