====== DHCP ======

**DHCP (Dynamic Host Configuration Protocol)** is a network protocol that automatically assigns IP configuration to devices on a network.

Instead of manually configuring every computer, DHCP provides network settings automatically when a device joins the network.

Typical information assigned by DHCP includes:

  * IP address
  * Subnet mask
  * Default gateway
  * DNS servers
  * Lease time

-----

===== Why Is DHCP Needed? =====

Without DHCP, every device would need to be configured manually.

For example:

<code>
IP Address:
192.168.1.25

Subnet Mask:
255.255.255.0

Default Gateway:
192.168.1.1

DNS Server:
8.8.8.8
</code>

For a home with a few devices this may be manageable, but for schools, offices, or enterprises with hundreds or thousands of devices, manual configuration would be impractical.

DHCP automates this process.

-----

===== How DHCP Works =====

When a device connects to a network, it typically performs four steps.

<code>
Client
   │
   │ 1. DHCP Discover
   ▼
DHCP Server
   ▲
   │ 2. DHCP Offer
   │
Client
   │
   │ 3. DHCP Request
   ▼
DHCP Server
   ▲
   │ 4. DHCP Acknowledgement (ACK)
   │
Client receives its IP configuration
</code>

This process is commonly called the **DORA** process:

  * **D**iscover
  * **O**ffer
  * **R**equest
  * **A**cknowledgement

-----

===== Example =====

A laptop joins a Wi-Fi network.

The DHCP server assigns:

<code>
IP Address:
192.168.1.25

Subnet Mask:
255.255.255.0

Gateway:
192.168.1.1

DNS:
8.8.8.8
</code>

The user does not need to enter any of these values manually.

-----

===== DHCP Lease =====

DHCP assigns addresses for a limited period called the **lease time**.

Example:

<code>
Lease Time

24 hours
</code>

Before the lease expires, the client usually requests to renew it.

If renewal succeeds, the device typically keeps the same IP address.

-----

===== DHCP Server =====

A DHCP server may be:

  * A home Wi-Fi router
  * A dedicated server
  * A firewall
  * A Layer 3 switch

In most home networks, the wireless router also acts as the DHCP server.

-----

===== Static vs Dynamic Addresses =====

A device may use either:

=== Dynamic Address ===

Assigned automatically by DHCP.

Suitable for:

  * Computers
  * Smartphones
  * Tablets
  * Guest devices

-----

=== Static Address ===

Configured manually.

Often used for:

  * Servers
  * Printers
  * Network cameras
  * Firewalls

-----

===== DHCP Reservation =====

Many DHCP servers support **reservations**.

A reservation means a particular device always receives the same IP address.

Example:

<code>
Printer

MAC Address

00:1A:2B:3C:4D:5E

↓

Always receives

192.168.1.100
</code>

This combines automatic management with predictable addressing.

-----

===== DHCP and IPv6 =====

IPv6 also supports DHCP.

However, IPv6 devices may obtain network information through:

  * Router Advertisements (RA)
  * DHCPv6
  * Both

Unlike IPv4, DHCP is not always required in IPv6 networks.

-----

===== What Happens If DHCP Fails? =====

If no DHCP server is available, a device may:

  * Fail to obtain an IP address.
  * Assign itself a link-local address.

Example (Windows):

<code>
169.254.x.x
</code>

Such an address allows limited communication within the local network but usually does not provide Internet access.

-----

===== DHCP and Telenegar =====

Current Telenegar Internet tools do not directly display DHCP information because DHCP operates only within the local network.

However, understanding DHCP helps explain why:

  * A device receives its IP address automatically.
  * Local network configuration changes.
  * Internet access may fail after connecting to a network.

-----

===== Common Misconceptions =====

  * **DHCP changes the MAC address.**
    * False. DHCP assigns IP configuration, not hardware addresses.

  * **DHCP always assigns a different IP address.**
    * False. A device often receives the same address repeatedly, especially if its lease is renewed.

  * **Only large organizations use DHCP.**
    * False. Almost every home router includes a DHCP server.

-----

===== Related Topics =====

  * [[networking:internet:ip-addresses|IP Addresses]]
  * [[networking:internet:default-gateway|Default Gateway]]
  * [[networking:internet:mac-address|MAC Address]]
  * [[networking:internet:subnetting|Subnetting]]
  * [[networking:internet:nat|Network Address Translation (NAT)]]

-----

{{tag>dhcp ip networking ipv4 ipv6 dora}}