# Setting up a DHCP Server on a Cisco Router

### <mark style="color:blue;">**Scenario:**</mark>&#x20;

You are configuring a <mark style="color:red;">**Cisco router as a DHCP server**</mark> to dynamically assign IP addresses to client devices on a local network.

### <mark style="color:blue;">**1. Understanding DHCP**</mark>

DHCP (Dynamic Host Configuration Protocol) automatically assigns <mark style="color:red;">**IP addresses**</mark>, <mark style="color:red;">**subnet masks**</mark>, <mark style="color:red;">**default gateways**</mark>, and other parameters to network devices. A Cisco router can function as a DHCP server, providing these settings to clients.

### <mark style="color:blue;">**2. Practical Scenario**</mark>

* You are setting up a small office network.
* The router will act as a DHCP server.
* The local network uses the **192.168.1.0/24** subnet.
* The router's interface (**FastEthernet0/0**) will be the gateway **192.168.1.1**.
* The DHCP server should assign addresses from **192.168.1.100 to 192.168.1.200**.
* Some devices (like a printer) will need **static IP reservations**.

### <mark style="color:blue;">3. Network Topology</mark>

<figure><img src="https://2804731566-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FLOszSitBb46QATDLUtW4%2Fuploads%2FkRHLp3iJh2g7XDpJpV2L%2F0476-topology.png?alt=media&#x26;token=746db07f-a56e-4ed3-ad0c-22350ee786c2" alt=""><figcaption><p>Topology</p></figcaption></figure>

### <mark style="color:blue;">**4. Configuration Steps**</mark>

#### **Step 1: Enter Global Configuration Mode**

Connect to the router via <mark style="color:red;">**CLI**</mark> (Console, SSH, or Telnet), then enter global configuration mode:

```
R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#
```

#### **Step 2: Exclude Reserved IP Addresses**

Reserve specific IP addresses that <mark style="color:red;">**should not be assigned**</mark> by DHCP (e.g., for the router, printers, and servers):

```
R1(config)#ip dhcp excluded-address 192.168.1.1 192.168.1.10
```

* **192.168.1.1** is the router’s IP.
* **192.168.1.2 – 192.168.1.10** are reserved for static devices.

#### **Step 3: Create a DHCP Pool**

Define a DHCP pool named <mark style="color:red;">**OFFICE\_NETWORK**</mark>:

```
R1(config)#ip dhcp pool OFFICE_NETWORK
R1(dhcp-config)#
```

#### **Step 4: Define the Network and Subnet Mask**

Specify the subnet for DHCP clients:

```
R1(dhcp-config)#network 192.168.1.0 255.255.255.0
```

#### **Step 5: Set Default Gateway**

Assign the router’s IP as the default gateway:

```
R1(dhcp-config)#default-router 192.168.1.1
```

#### **Step 6: Define the DNS Server**

Specify a DNS server (e.g., Google’s **8.8.8.8**):

```
R1(dhcp-config)#dns-server 8.8.8.8
```

#### **Step 7: Configure the Lease Time**

Set a lease duration (e.g., **24 hours**):

```
R1(dhcp-config)#lease 1 0 0
```

`1 0 0` means **1 day, 0 hours, 0 minutes**.

#### Step 8: Exit the DHCP Configuration

```
R1(dhcp-config)#exit
R1(config)#
```

#### Step9: Assign IP address to **fastEthernet 0/0** (Connected to PC1)

```
R1(config)#interface fastEthernet 0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shutdown
```

#### Step 9: PC1 Configuration

```
PC1> ip dhcp
DORA IP 192.168.1.11/24 GW 192.168.1.1

PC1> show ip

NAME        : PC1[1]
IP/MASK     : 192.168.1.11/24
GATEWAY     : 192.168.1.1
DNS         : 8.8.8.8
DHCP SERVER : 192.168.1.1
DHCP LEASE  : 86395, 86400/43200/75600
MAC         : 00:50:79:66:68:00
LPORT       : 20008
RHOST:PORT  : 127.0.0.1:20009
MTU         : 1500

PC1>
```

#### Step 10: Printer (Static IP)

* Manually set **IP: 192.168.1.2**, **Gateway: 192.168.1.1**.
* Ensure it doesn’t request DHCP.

```
PC2> ip 192.168.1.2/24 192.168.1.1
Checking for duplicate address...
PC2 : 192.168.1.2 255.255.255.0 gateway 192.168.1.1

PC2> show ip

NAME        : PC2[1]
IP/MASK     : 192.168.1.2/24
GATEWAY     : 192.168.1.1
DNS         :
MAC         : 00:50:79:66:68:01
LPORT       : 20010
RHOST:PORT  : 127.0.0.1:20011
MTU         : 1500

PC2>
```

### <mark style="color:blue;">**5. Verifying DHCP Configuration**</mark>

#### **1. Check the DHCP Configuration**

```
R1#show ip dhcp pool

Pool OFFICE_NETWORK :
 Utilization mark (high/low)    : 100 / 0
 Subnet size (first/next)       : 0 / 0
 Total addresses                : 254
 Leased addresses               : 0
 Pending event                  : none
 1 subnet is currently in the pool :
 Current index        IP address range                    Leased addresses
 192.168.1.1          192.168.1.1      - 192.168.1.254     0
R1#
```

This shows the active DHCP pool and available IP addresses.

#### 2. View DHCP Bindings (Leased IPs)

```
R1#show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address          Client-ID/              Lease expiration        Type
                    Hardware address/
                    User name
192.168.1.11        0100.5079.6668.00       Mar 23 2025 05:54 AM    Automatic
R1#
```

This displays assigned IP addresses and MAC addresses.

### <mark style="color:blue;">**7. Troubleshooting Commands**</mark>

* Check if the DHCP service is running:

```
R1#show running-config | inclu
R1#show running-config | include dhcp
ip dhcp excluded-address 192.168.1.1 192.168.1.10
ip dhcp pool OFFICE_NETWORK
R1#
```

* Debug DHCP process:

```
R1#debug ip dhcp server events
DHCP server event debugging is on
```

### <mark style="color:blue;">Keywords</mark>

`DHCP`, `Cisco Router`, `IP Address`, `Subnet Mask`, `Default Gateway`, `DNS Server`, `Lease Time`, `Excluded Address`, `DHCP Pool`, `Network Configuration`, `IP Binding`, `DHCP Reservation`, `Dynamic IP`, `Static IP`, `Show Commands`, `Debugging`, `Packet Tracer`, `Network Automation`, `Router Configuration`, `CCNA`, `سیسکو`