How does DHCP (Dynamic Host Configuration Protocol) allocate IP addresses in a network?

Dynamic Host Configuration Protocol (DHCP) is a network protocol used to automatically assign and manage IP addresses and other network configuration information to devices in a network. The process of DHCP allocation involves several steps:

  1. DHCP Discovery:
    • When a device (client) joins a network, it sends a DHCP Discover broadcast message to discover available DHCP servers on the network.
    • This broadcast message is typically sent as a UDP packet to the destination IP address and the destination port 67.
  2. DHCP Offer:
    • DHCP servers on the network respond to the DHCP Discover message with a DHCP Offer.
    • The DHCP Offer includes an available IP address and other configuration parameters (subnet mask, default gateway, DNS server, lease duration, etc.).
    • The server sends this response as a UDP packet to the client's IP address (typically and port 68.
  3. DHCP Request:
    • The client receives multiple DHCP Offers (if there are multiple DHCP servers) and chooses one based on certain criteria (such as the first response received).
    • The client then sends a DHCP Request message to the selected DHCP server, indicating its acceptance of the offered configuration.
  4. DHCP Acknowledgment:
    • The DHCP server that receives the DHCP Request sends a DHCP Acknowledgment (ACK) to the client, confirming the allocation of the IP address and providing the final set of configuration parameters.
    • This message is sent to the client's IP address and port 68.
  5. Configuration Renewal:
    • The client uses the allocated IP address and network configuration for a specific lease duration.
    • Before the lease expires, the client can request a renewal by sending a DHCP Request to the DHCP server that originally provided the lease.
  6. Configuration Release:
    • If a device no longer needs the allocated IP address or is leaving the network, it can send a DHCP Release message to the DHCP server to release the IP address back to the pool.
  7. Address Pool Management:
    • DHCP servers manage a pool of available IP addresses. When a device requests an IP address, the DHCP server assigns an available address from the pool.
    • The server keeps track of leased IP addresses, lease durations, and other configuration details to avoid conflicts.
  8. Conflict Detection:
    • DHCP servers typically perform conflict detection before assigning an IP address to ensure that the chosen address is not already in use on the network.