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.
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.