That's where DHCP comes in.

First, why does my device even need an IP address?

IP address is the address our device uses to communicate over a network.

When I open a website, my laptop needs to send and receive data. For that communication to work, it needs an IP address.

So, what exactly is DHCP?

DHCP stands for Dynamic Host Configuration Protocol.

In simple terms, it automatically provides devices with IP addresses and other network settings, such as the default gateway and DNS servers.

Without DHCP, I’d have to configure these settings manually on every device.DHCP saves us from that hassle.

But how does a device automatically receives an IP address when it doesn’t even have one yet?

That's where things get interesting.

The DORA process: It’s how DHCP assigns an IP address

DHCP follows a four-step process called DORA.

DORA stands for:

- Discover

- Offer

- Request

- Acknowledge

Here's how I understand it:

my device asks for network configuration, a DHCP server offers an available address, my device requests that address, and the server confirms the assignment.

Now, let's break down what happens at each step.

1. Discover: My device looks for a DHCP server

When my laptop joins a network, it needs an IP address, but it doesn't have a valid one yet.

So, it sends a DHCP Discover message to find a DHCP server.

Because the laptop doesn't know the server's address, it initially sends a broadcast on the local network.

In a typical IPv4 DHCP exchange, the client uses "0.0.0.0" as its source IP and "255.255.255.255" as the destination IP.

Basically, my laptop is asking:

"Is there a DHCP server here that can give me an IP address?"

2. Offer: The server responds

The DHCP server receives the Discover message and checks which addresses it can offer from its configured address pool.

It then sends a DHCP Offer containing a proposed IP address and other configuration information.

For example, the server might offer "192.168.1.25".

My laptop now has an offer, but the address hasn't been fully assigned yet.

3. Request: My device chooses an offer

My laptop sends a DHCP Request to indicate that it wants to use the offered IP address.

This message also helps DHCP servers identify which offer the client has selected, particularly when multiple servers respond.

Think of it as saying:

"I'd like to use the address you offered me."

4. Acknowledge: The server confirms the assignment

Finally, the DHCP server sends a DHCP Acknowledgment, commonly called DHCP ACK.

This confirms the lease and provides the configuration the client should use.

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My laptop can now configure its network interface with the assigned IP address and communicate over the network.

That's the DORA process: Discover, Offer, Request, Acknowledge.

Four messages, and my device has its network configuration without me manually entering an IP address.

But where do these broadcast messages actually go?

This was one of the things I wanted to understand better.

When my laptop broadcasts a DHCP Discover message, does every device connected to the internet receive it?

No.

The initial broadcast is confined to the local Layer 2 broadcast domain, typically the same VLAN.

A router doesn't normally forward an IPv4 limited broadcast such as "255.255.255.255" to other networks.

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So, what happens if the DHCP server is on a different network?

That's where a DHCP relay agent comes in. It forwards DHCP requests between the client's network and a DHCP server on another network.

This allows organizations to serve multiple networks without needing a separate DHCP server on every subnet.

Does my device get the same IP address every time?

Not necessarily.

DHCP generally assigns IP addresses through a lease, meaning the client can use the address for a specified period.

When the lease approaches expiration, the client can attempt to renew it.

If I disconnect from Wi-Fi and reconnect later, I might receive the same address again. But DHCP can assign a different one, depending on the server's configuration and address availability.

The important thing is that dynamic addressing doesn't mean my IP address must change every time I connect.

It means the address is managed through DHCP rather than requiring manual configuration.

If DHCP keeps reusing IP addresses, why is IPv4 running out?

This was another question I had.

IPv4 uses 32-bit addresses, providing approximately 4.3 billion possible address combinations.

That might sound like a lot, but there are far more devices and network connections than there are publicly usable IPv4 addresses.

DHCP helps manage address allocation, but it doesn't create additional IPv4 addresses.

And there's another important piece: NAT, which stands for Network Address Translation.

NAT allows multiple devices on a private network to share a public IPv4 address when communicating with external networks.

For example, my laptop, phone, and smart TV can all use private IP addresses on my home Wi-Fi while sharing the same public IPv4 address for internet access.

That's one reason a household doesn't need a separate public IPv4 address for every device.

DHCP and NAT solve different problems: DHCP manages network configuration, while NAT translates addresses between networks.

What happens if DHCP fails?

If a device can't obtain a valid IP configuration, it might not be able to communicate normally on the network.

A few possible causes include:

- The DHCP server is unavailable.

- The address pool has no available addresses.

- A network or relay configuration is incorrect.

- The device can't communicate with the server.

On some operating systems, a device may automatically assign itself an IPv4 link-local address in the "169.254.0.0/16" range.

However, that doesn't mean DHCP has successfully assigned an address. Link-local addressing is intended for communication on the local link and doesn't provide normal internet connectivity by itself.

So, when a device connects to Wi-Fi but can't access the internet, DHCP is one of the things worth checking.

What I took away from learning DHCP

Before looking into DHCP, I knew my devices received IP addresses automatically. I just hadn't thought much about what made that possible.

Now, I understand that there's a process behind it.

My device discovers a DHCP server, receives an offer, requests an address, and gets confirmation through the DORA process.

I also learned that DHCP broadcasts don't travel everywhere, leases help manage address allocation, and DHCP isn't the same thing as NAT.