Dynamic Host Configuration Protocol (DHCP)

DHCP is a mechanism for centralizing the assignment of Internet Protocol (IP) addresses and other network parameters within a network segment. A workstation configured to use DHCP operates in four main phases:

1. Server Discovery: The DHCP client sends a broadcast DHCPDISCOVER message to the network subnet to locate any available DHCP servers.

2. IP Lease Offer: When a DHCP server receives the DHCPDISCOVER message, it reserves an IP address and responds by sending a DHCPOFFER message back to the DHCP client.

3. IP Lease Request: The DHCP client responds to the offer by broadcasting a DHCPREQUEST message to the server, formally requesting the offered IP address.

4. IP Lease Acknowledgement: The DHCP server receives the DHCPREQUEST message and sends a DHCPACK packet back to the client. This packet includes the lease duration and configuration details such as the assigned IP address, subnet mask, default gateway, and DNS server information.

If Media Access Control (MAC) reservations (also known as DHCP reservations) are configured on the DHCP server, the IP address assigned to a network interface card (NIC) will always remain the same, regardless of the lease length. This eliminates the need for DNS resolution at the workstation, but requires additional configuration on the DHCP server.

Why use MAC reservations, rather than assigning IPs manually?

As a protocol, DHCP can specify a Proxy Auto Configuration (PAC) endpoint and define static IP routes. In complex LAN environments—such as those found in casinos, resorts, and stadiums—these capabilities offer significant advantages.

Windows CAL, running on Microsoft Windows 7 or later, supports the use of PAC scripts.

Why not use DHCP?

When a client uses DHCP, its IP address is typically not fixed and can change throughout the day based on the lease duration. This variability can cause issues with peer-to-peer communications. One solution is to use DNS name resolution; however, this requires each message sent to a workstation to be verified through the DNS server or cache to ensure the IP address remains valid. This additional step can cause latency.