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Home > Success Center > IP Address Manager (IPAM) > IPAM Administrator Guide > DHCP management > DHCP Split Scopes

DHCP Split Scopes

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Created by Nanette.Neal, last modified by Nanette.Neal on Jul 15, 2016

Views: 89 Votes: 0 Revisions: 3

Split scopes can be used to for several reasons:

  • Provide load balancing between two DHCP servers.
  • Ensure high availability DHCP services for your network.

The IPAM Summary page displays the Top 10 DHCP Scopes by Utilization with Split Scopes Resource.

File:Success_Center/New_Articles/IPAM_AdminGuide_MT/050/0F0/scopes.png

You can edit the resource by selecting a sort order and by using SQL Filters to limit the which scopes are displayed.

File:Success_Center/New_Articles/IPAM_AdminGuide_MT/050/0F0/editSplitScopes.png

Mousing over a scope displays a Tool Tip window.

When you split a scope, the primary server is responsible for a certain group of IP addresses, and the secondary is responsible for the remainder. An offer delay (generally between 1000 and 5000 milliseconds) is set for the secondary server to ensure that if the primary server is unable to provide an IP address within the offer delay time, the secondary server will do so using its pool of addresses.

Scopes are usually split into one of two configurations:

  • 50/50, where half of the IP addresses are on the primary DHCP server and half are on the secondary server. This configuration is usually used for load balancing.
  • 80/20, where 80% of the IP addresses are on the primary DHCP server and only 20% are on the secondary server. This configuration is generally to ensure high availability.

When a scope is split, the result is two scopes, each of which excludes the IP addresses that the other scope (and server) manages. For example:

You start with a scope01 on your primary DHCP server. Scope01 includes the entire subnet of 10.10.10.0/24 (254 IP addresses), with no exclusions. You split scope01, and name the second scope scope02 on your secondary DHCP server. You choose an 80/20 split.

Now, scope01 will still span the entire subnet, but will exclude the last 20% of the addresses in that subnet (10.10.10.204-254). Scope02 will also span the entire subnet, but will exclude the first 80% of the addresses in that subnet (10.10.10.1-203).


  • Splitting scopes on some Cisco DHCP servers may require you to perform additional configuration steps on the servers themselves.
  • You must have two DHCP servers of the same type to split a scope between them.
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