Summary
Highlights
Before DHCP, IP configuration was manual, requiring administrators to input IP addresses, subnet masks, gateways, and DNS servers for each device. With thousands of devices on modern networks, this became impractical, leading to the creation of DHCP in 1997. DHCP automates the assignment of IP address information, making network connectivity seamless for users.
The automated process of obtaining an IP address through DHCP is known as DORA. It begins with a 'Discover' message from a client without an IP address (0.0.0.0 on UDP port 68) broadcast across the network. A DHCP server then sends an 'Offer' (broadcast to 255.255.255.255) with a proposed IP address. The client 'Requests' the offered IP, and finally, the DHCP server sends an 'Acknowledge' (broadcast from UDP port 67 to UDP port 68) to confirm the IP address assignment and lease duration.
The DHCP server uses a 'scope,' a predefined list of IP addresses and configuration settings, to assign IP addresses. This scope includes available IP addresses for devices, excluded addresses (e.g., for static devices like routers), subnet masks, lease durations, and other IP configuration options like DNS servers and default gateways. Within the scope, 'address pools' are large ranges of IP addresses from which the DHCP server assigns IPs to connecting devices.
A DHCP scope configuration, as seen in Windows Server, includes an address pool specifying the range of IPs available. Administrators can also view active leases and configure advanced options. It allows for the management of the entire IP address distribution within a specific subnet.
DHCP reservations ensure that a specific device always receives the same IP address when it connects to the network. This is useful for devices like file servers, web servers, or routers that require a consistent IP. Instead of manually configuring static IPs on each device, reservations are set on the DHCP server by associating a device's MAC address with a particular IP address. This simplifies management, especially when IP addressing schemes change.