DHCP Information

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The Dynamic Host Configuration Protocol (DHCP) is a mechanism that allows computers on a network to automatically receive its network configuration, including its IP address, from a central server.

Advantages of DHCP

Both users and network administrators benefit from the use of DHCP. The advantages for users are:

• Users are able to connect new machines to the network and automatically obtain their IP address, default gateway, DNS server, WINS server, and default DNS domain name.
• DHCP substitutes the manual entry of the above items.
• Allows notebook users to roam between different network environments without configuration changes.
• Avoids errors in configuration. Once the DHCP service is configured correctly, mistakes are lessened due to the automatic management of network configuration by the DHCP server. For example, accidental assignment of duplicate IP addresses can be avoided.
• Allows for the configuration or reconfiguration of a large number of computers in a short amount of time.
• Changes in network configuration can be applied transparently. For example, users do not need to change their configuration to use a new DNS server or new default gateway.

The benefits for network administrators are:

• Lessen the likelihood of configuration errors.
• Allows network authentication via MAC address registration.
• Simplify management of network configuration changes and migrations. For example, one DNS server can be brought down and DHCP clients directed to use a different DNS server.
• Efficient use of scarce IP address space.
• Eases the administration of IP addresses.

IP Address Allocation Strategy

The IP address allocated to a client is actually leased for a fixed period of time. This allows the DHCP server to automatically recover and reallocate IP addresses when clients shut down or are disconnected from the network. The IP addresses can still be recovered even when the clients do not gracefully release their leases.

Even though a DHCP server uses a dynamic IP address allocation strategy, a DHCP client can still receive a fairly static IP address.

A DHCP server remembers the IP address that it has assigned to a client, even when the lease has already expired. When the same client subsequently requests for an IP address, the DHCP server will offer the same IP address that was previously allocated to it. The DHCP server avoids reassigning this IP address to another client, unless there is no other free IP address available to offer to a new client.

Myths about DHCP

It is not uncommon for users in environments that had previously assigned static IP addresses to be somewhat resistant to the migration to DHCP. Most of the reasons offered for their resistance tend to be due to misunderstandings:

1. Others cannot find my computer if there is no fixed well-known address.

   This is one of the most common reason, and which of course is not correct. We have a whole document to deal with this topic: DHCP and Dynamic DNS.

2. Network access for DHCP IP addresses is slower or less reliable.

   The routers and switches on the network doesn't care about how IP addresses were assigned. An IP address is an IP address.

Related information:

DHCP and Dynamic DNS
DHCP Configuration Guide
Troubleshooting DHCP Problems