DHCP stands for dynamic host configuration protocol and is a network protocol used on IP networks where a DHCP server automatically assigns an IP address and other information to each host on the network so they can communicate efficiently with other endpoints.
In addition to the IP address, DHCP also assigns the subnet mask, default gateway address, domain name server (DNS) address and other pertinent configuration parameters. Request for comments (RFC) 2131 and 2132 define DHCP as an Internet Engineering Task Force (IETF)- defined standard based on the BOOTP protocol.
A DHCP Server is a network server that automatically provides and assigns IP addresses, default gateways and other network parameters to client devices. It relies on the standard protocol known as Dynamic Host Configuration Protocol or DHCP to respond to broadcast queries by clients.
A DHCP server automatically sends the required network parameters for clients to properly communicate on the network. Without it, the network administrator has to manually set up every client that joins the network, which can be cumbersome, especially in large networks. DHCP servers usually assign each client with a unique dynamic IP address, which changes when the client’s lease for that IP address has expired.
Components of DHCP
When working with DHCP, it’s important to understand all of the components. Below is a list of them and what they do:
- DHCP server: A networked device running the DCHP service that holds IP addresses and related configuration information. This is most typically a server or a router but could be anything that acts as a host, such as an SD-WAN appliance.
- DHCP client: The endpoint that receives configuration information from a DHCP server. This can be a computer, mobile device, IoT endpoint or anything else that requires connectivity to the network. Most are configured to receive DHCP information by default.
- IP address pool: The range of addresses that are available to DHCP clients. Addresses are typically handed out sequentially from lowest to highest.
- Subnet: IP networks can be partitioned into segments known as subnets. Subnets help keep networks manageable.
- Lease: The length of time for which a DHCP client holds the IP address information. When a lease expires, the client must renew it.
- DHCP relay: A router or host that listens for client messages being broadcast on that network and then forwards them to a configured server. The server then sends responses back to the relay agent that passes them along to the client. This can be used to centralize DHCP servers instead of having a server on each subnet.
The Benefits of a dedicated DHCP Server
A better approach than trying to use DHCP on your router/switch is to use a centralized DHCP server. This is particularly true for network environments that require support of both DHCP for IPv4 and DHCP for IPv6 at the same time. Virtually all DHCP server vendors support both protocols so you can use the same management interface for IPv4 and IPv6. There are several benefits that make it advantageous for an enterprise to use DHCPv6.
- Having a DHCPv6 server that is integrated into your IP Address Management (IPAM) system for IPv6 gives visibility to the IPv6-enabled client nodes.
- You also would want this same functionality for IPv4. As IPv4 address space becomes increasingly constrained, you will want to keep track of your DHCP scopes and determine if your lease time is adequate with the plethora of BYOD systems joining your networked environment.
- DHCP servers provide logging and management interfaces that aid administrators manage their IP address scopes. Your organization will want an accounting of what is on your network regardless of IP version being used.
- DHCP servers can provide redundancy and high availability. If one DHCP server were to fail, the clients will preserve their current IP addresses and not cause an interruption for the end-nodes.
- Organizations will prefer a DHCPv6 server that has been tried and tested. For example, The Infoblox DHCPv6 server has been certified as “IPv6 Ready” by the USGv6 certification laboratory.
Organizations that are beginning to implement IPv6 should migrate DHCP for IPv4 scope off the routers/switches and put them on a robust DHCP server infrastructure. This change will also mean that your organization would want to have DHCP operate the same for both protocols. Enterprise organizations will want to take advantage of the centralized dual-protocol DHCP server to provide IPv4 and IPv6 addresses to client devices.
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