SYS‐255 Lab 4 DHCP - aljimenez28/champlain GitHub Wiki

Objective

Install and configure an ISC DHCP server on Rocky Linux to provide dynamic IP addresses to Windows clients.
Verify operation with logs, Wireshark captures, and lease-time changes.

Key Steps & Commands

1. Connect to DHCP Server

Used PuTTY from AD01 to SSH into the Rocky Linux VM:
```
ssh [email protected]
```

2. Install and Prepare DHCP

sudo yum install dhcp
sudo -i                     # elevate to root

Backed up the default config:

cp /etc/dhcp/dhcpd.conf /etc/dhcp/dhcpd.conf.bak

3. Edit DHCP Configuration

Opened the config file:
```
sudo vi /etc/dhcp/dhcpd.conf
```

Final working configuration:

default-lease-time 3600;
max-lease-time 14400;
subnet 10.0.5.0 netmask 255.255.255.0 {
option routers 10.0.5.2;
option subnet-mask 255.255.255.0;
option domain-name "alejandra.local";
option domain-name-servers 10.0.5.5;
range 10.0.5.101 10.0.5.125;
}

4. Test & Start the Service

Validate syntax:
```
sudo dhcpd -t -cf /etc/dhcp/dhcpd.conf
```

Start and enable service:

sudo systemctl start dhcpd
sudo systemctl status dhcpd
sudo systemctl enable dhcpd

5. Configure Firewall

sudo firewall-cmd --add-service=dhcp --permanent
sudo firewall-cmd --reload
sudo firewall-cmd --list-all   # confirm 'dhcp' is listed

6. Configure Client

On wks01, set the network adapter to Obtain an IP address automatically.
Verified lease with:
```
ipconfig /all
```
- Received IP 10.0.5.101, Gateway 10.0.5.2, DHCP Server 10.0.5.3.

7. Verify Server Logs

sudo cat /var/log/messages | grep -i wks01-alejandra

Confirmed the DHCPOFFER, DHCPREQUEST, and DHCPACK messages.

8. Wireshark Capture

Captured the 4-message DHCP handshake (Discover, Offer, Request, Ack) on WKS01 during ipconfig /release and ipconfig /renew.

Problems & Solutions

Problem	Cause	Solution
Unit dhcp.service not found	Used wrong service name	Correct service name is dhcpd
Job for dhcpd.service failed… expecting left brace	Used ( instead of { in subnet declaration	Edited config to use {
range declaration not allowed here	Missing closing brace/semicolon	Added } and ;
Permission denied when viewing config	File owned by root	Ran commands with sudo
Lease times not updating	Needed to add lease lines outside subnet	Added default-lease-time and max-lease-time at top of file

Important Tips

Always run sudo dhcpd -t -cf /etc/dhcp/dhcpd.conf before starting the service to catch syntax errors.
Every line inside the subnet block needs a semicolon.
Use sudo for reading or editing /etc/dhcp/dhcpd.conf.
Remember to open the firewall and reload rules or clients will not receive offers.
Verify client leases with ipconfig /all and server logs with grep.

Reflection

This lab reinforced the importance of careful syntax in configuration files and the value of testing (dhcpd -t) before starting a service.
It also highlighted common DHCP troubleshooting steps such as checking logs, firewall rules, and lease times on both server and client sides.