Managing DHCP scopes

What is a DHCP Scope?

A DHCP scope is a fundamental component of the DHCP server, defining a specific range of IP addresses that the server can allocate or lease to devices on a network. in DHCP defined as a pool of IP addresses that a DHCP server can dynamically assign to clients on a particular subnet. 

DDI Central supports the following network topological elements that can organize the DHCP scopes in IP network infrastructure:

Subnets

• A subnet represents a basic segment of IP addresses (IPv4 or IPv6) within a network. Defining, a subnet in DDI Central is used to define a range of IP addresses that the DHCP server can assign to clients on a specific network segment.
• Each subnet is defined by a range of IP addresses and a subnet mask, determining the network's address range.
• To create or update a subnet go to DHCP-> Network-> Subnet.
• Define a new subnet by providing values for various attributes of the subnet like:
  Provide the first address of the pool to be associated with the new subnet.
• Provide a suitable description for the subnet to quickly identify its purpose and convey the policy associated with it, for a common understanding of its layout.
• Specify the subnet size using an appropriate prefix, which denotes the number of IP addresses that the subnet can accommodate.
• Enable DHCP failover and select a DHCP server to take over the task of assigning IP addresses for the subnet without any significant downtime.
• Assign the necessary DHCP options. 
• Click Save.
• Note: DDI Central also offers the option to clear the active subnets currently in lease. Clearing all the leases for a subnet removes it from your database, freeing up memory, but lease records stay intact, enabling IP addresses to revert to their original states as per the lease records after a short interval of 5 minutes.

Address Pools

• An address pool within a subnet specifies the range of IP addresses available for dynamic assignment.
• Pools are used to control the distribution of IP addresses to clients within a subnet. They allow for more granular management of IP address allocations, including setting different options or restrictions for different pools within the same subnet.
• When configuring options at the subnet level, you can add and define the pool or address range within the subnet that should be configured with a specific set of options. Multiple combinations of options can be applied to various address ranges within the same subnet.

• Address pool configurations in a subnet can either allow or deny specific client classes for dynamic IP provisioning. If "Allow" is set to "yes," the pool permits provisioning for the chosen client class, while setting it to "NO" excludes provisioning for that class. Choosing "none" means the address pool is open for dynamic provisioning to all clients in the subnet without class restrictions.
  
   
   

   Static subnets 

  Static subnets refer to segments of a network that have fixed IP addresses assigned to them. Unlike dynamic subnets, where IP addresses can be assigned on-the-fly by a DHCP server, static subnets have pre-defined IP ranges and the IP addresses are usually assigned manually to devices.

  To define  a static subnet in DDI Central:

  • Select DHCP-> Network. On the Network page, navigate to the Static Subnet tab. You can either click the Add Static Subnet button in the top right corner of the page or click the Import button to import the spreadsheet you use to maintain the static subnet leases.
     

  • On clicking the Add Static Subnet button, the Create Static Subnet page appears, prompting you to enter the essential details for the static subnet, like the Network Address and network prefix of the static subnet, a suitable description to identify the static subnet and you can also map the Static subnet to a Supernet to position it hierarchically in the tree view of your cluster's  IP address plan. You can also specify if this subnet is associated with a VLAN by entering the targeted VLAN details and then click Save to finalize the configurations for the Static Subnet.
    
    
     

  • Once you create and define the IP address space for a static subnet, the entry you just created will be displayed under the static Subnet tab in the Network page. Here you can click on the Import button available in the top right corner to import the static subnet's lease details you maintain in a spreadsheet.  
    More on Static Leases here.
     

  • Once the Static Leases are successfully imported, the capacity and other details of the Static Subnet are reflected under the Static Subnet tab on the Network page. On clicking through the targeted static subnet entry on this page, will immediately redirect you to the IPAM->Lease->Static Leases page, where you will see the leases pertaining to the specific Static Subnet you clicked on.
     

Shared Networks

• A shared-network defined in DDI Central is used when multiple logical IP networks (subnets) share the same physical network segment.
• Shared networks allow DHCP to serve multiple subnets on a single physical network, providing different IP configurations to clients based on their network segment.
• To create a new shared network, go to DHCP-> Network-> Shared Network.
• Assign a unique name and description for the shared network.
• Just add the required subnets and apply the necessary DHCP or custom options .
• Click Save.
  
  

Special Case for Windows:
No options cannot be assigned for a shared network in Microsoft DHCP.

Hosts or DHCP reservations

• A host declaration specifies settings for individual clients based on their hardware (MAC) address.
• This is used for assigning fixed IP addresses or specific configurations to particular clients, ensuring that a specific client always receives the same IP address and settings.
• To create a Host with a fixed address, go to DHCP-> Network-> Host.
• On the Host page, provide a unique name for the host, the mac address of the host.
  
  
  
   

Host Groups

• Host groups are a group of hosts combined logically for easier management.
• Grouping hosts can simplify configuration, especially in large networks, by applying common settings to multiple hosts.

• You can apply a multiple DHCP options over this combination of hosts for customized management.
  
   

  Special case for Microsoft DHCP:
  Host Groups are not available in Microsoft DHCP.

Supernets

• Supernets, or supernetting, refers to aggregating multiple networks into a larger network. In the context of DHCP, this is not a direct feature but rather a concept of network design.
• Supernetting is used in IP routing more than in DHCP configurations. It's about combining smaller subnets into a larger address space for routing purposes.
   

VLANs (Virtual LANs)

• VLANs are a network configuration that segments a physical network into multiple logical networks at the data link layer (Layer 2).
• DDI enables DHCP servers to serve different VLANs as distinct subnets or shared networks.
• Each VLAN you create within a subnet functions as a separate network, which improves performance by reducing broadcast traffic, enhances security by isolating sensitive data, and simplifies management by grouping devices according to function, department, or project.You can also associate an already existing VLAN to the subnet.
• Name and provide a suitable description to quickly identify the new VLAN. Also assign a suitable VLAN ID.
• Note: VLAN IDs are represented by a 12-bit number, but the usable range of VLAN IDs is from 2 to 4094.

Note: DDI Central enables you to define Supernets and VLANs only to simplify network administration. However, no advanced DHCP configurations, such as DHCP options or Client Classes, can be implemented on the Supernets and VLANs.

Also, when discovering your current configurations from your network infrastructure using DDI Central discovery tools, it's crucial to note that VLANs and Supernets configured in your network will not be discovered. Therefore, ensure that you configure them separately in DDI Central for comprehensive and accurate network management.

DHCP scope visualization

DDI Central also lets you organize and manage the scopes in a hierarchical manner by providing hierarchical tree-view that show how different scopes relate to one another within the network. The DHCP scope tree view enables admins to quickly locate and access specific scopes, subnets, to manage configurations and troubleshooting tasks for a specific scope.

DDI Central provides flexible and powerful ways to manage IP address assignment and network configurations. Understanding these elements is crucial for network administrators to effectively design and manage their network's IP addressing scheme.