Dynamic Host Configuration Protocol (DHCP) service lets you administer and distribute IP addresses to computers from your server, and simplifies configuring and adding client computers to your network. When you configure the DHCP server, you assign a block of IP addresses that can be made available to clients.
Each time a computer configured to use DHCP starts up, it looks for a DHCP server on your network. If it finds a DHCP server, the client computer requests an IP address. The DHCP server sends an available IP address to the computer, along with a lease period (the length of time the client computer can use the address) and configuration information.
Organizations can benefit from the features of DHCP service, such as the ability to set Domain Name System (DNS) and search domain options for computers without needing to configure each client. Also, if your organization has more clients than IP addresses, you can benefit from using DHCP service. IP addresses are assigned as needed, and when they’re not needed, they can be used by other clients. You can use a combination of static and dynamic IP addresses for your network.
You can use the Server app to:
Configure and administer DHCP service
Create and administer networks
Configure DNS and search domain options for client computers
View DHCP address leases
Create networks
DHCP networks are groups of computers on a network that simplify administration. You can organize DHCP networks any way that’s useful to you. For example, you can create DHCP networks for groups in your organization or for floors of a building.
After you group computers into networks, you can configure options for all computers on a network at one time instead of individually.
Each network typically needs a hardware device called a router to connect to other networks.
Assign dynamic IP addresses
With dynamic address allocation, an IP address is assigned for a limited period of time (the lease time) or until the computer doesn’t need the IP address, whichever comes first.
By using short leases, DHCP can reassign IP addresses on networks that have more computers than IP addresses. Leases are renewed if the address isn’t needed by another computer.
Addresses allocated to VPN clients are distributed like DHCP addresses, but they don’t come out of the same range of addresses as DHCP. If you plan on using VPN, leave some addresses unallocated by DHCP for use by VPN.
Use static IP addresses
Static IP addresses are manually assigned to a computer or device once, then don’t change. You can assign a static IP address to any computer that must have a continuous network presence, such as a web server. Other devices that must be continuously available to network users, such as printers, can also benefit from a static IP address.
Static IP addresses can be set up manually by entering the IP address on the computer (or other device) that’s assigned the address, or by configuring DHCP to provide the same address to a specific computer or device on each request.
If you configure clients with static IP addresses using DHCP (also called DHCP static maps), you can also configure them with fixed host names by configuring your DNS service.
Manually configured static IP addresses avoid potential issues involved with DHCP-assigned addresses, and they don’t suffer from the delay of receiving an address.
DHCP-assigned addresses permit address configuration changes on the DHCP server rather than on each client.
Don’t include manually assigned static IP address ranges in the range distributed by DHCP.
Locate the DHCP server
When a computer looks for a DHCP server, it broadcasts a message. If your DHCP server is on a different network from the computer, make sure the routers that connect your networks can forward client broadcasts and DHCP server responses.
A relay agent or router on your network that can relay BootP communications works for DHCP. If you don’t have a way to relay BootP communications, place the DHCP server on the same network as your client.
Interact with other DHCP servers
You might already have DHCP servers on your network, such as an AirPort Base Station or Time Capsule.
The DHCP service in the Server app can coexist with other DHCP servers as long as each DHCP server uses a unique pool of IP addresses.
If each AirPort Base Station or Time Capsule is on a separate network, configure your routers to forward client broadcasts and DHCP server responses as described in “Locate the DHCP server.”
You can have multiple DHCP servers on the same network. However, they must be configured properly to avoid conflict. Each server needs a unique pool of IP addresses to distribute.
Assign reserved IP addresses
Some IP addresses can’t be assigned, including addresses reserved for loopback and broadcasting. If you try to configure DHCP to use these addresses, you’re warned that the addresses are invalid.