LFCS: Networking (25%)

This section covers systemLinux administrationnetworking, taskshostname relatedresolution, totime configuringsynchronization, theOpenSSH, kernel,packet managingfiltering, processes,routing, jobs, software, hardware recovery,bridges, and containers.load balancing.

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1. Configure KernelIPv4/IPv6 ParametersNetworking & Hostname Resolution

Learn

• TemporaryAssign IP addresses (runtime)static vs& persistent kernel parameters.dynamic).
• Tools:Configure hostnames and DNS resolution.

Understand sysctl/etc/hosts, /etc/resolv.conf, and /etc/sysctl.confhostnamectl.

Commands

# ShowView allnetwork parametersinterfaces
sysctlip -aaddr show
ip link show

# Configure static IP (example)
sudo nmcli con mod eth0 ipv4.addresses 192.168.1.100/24
sudo nmcli con mod eth0 ipv4.gateway 192.168.1.1
sudo nmcli con mod eth0 ipv4.dns 8.8.8.8
sudo nmcli con mod eth0 ipv4.method manual
sudo nmcli con up eth0

# Set ahostname
runtimehostnamectl parameterset-hostname sudomyhost
sysctlhostnamectl net.ipv4.ip_forward=1status

# PersistDNS parametercheck
across reboots
echo "net.ipv4.ip_forward = 1" | sudo tee -acat /etc/sysctl.resolv.conf
sudoping sysctl -pgoogle.com

Exercises

1. EnableAssign a static IP forwardingto temporarilyan interface and checkverify status.connectivity.
2. MakeChange IPthe forwardinghostname permanent.and update /etc/hosts accordingly.

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2. ManageTime Processes and ServicesSynchronization

Learn

• Identify, monitor, and troubleshoot processes.

Systemd services management.

Commands

# Process management
ps aux | grep <name>
top
htop       # if installed
kill <PID>
kill -9 <PID>

# Systemd service management
systemctl status <service>
systemctl start <service>
systemctl stop <service>
systemctl enable <service>
systemctl disable <service>
systemctl restart <service>
systemctl reload <service>

Exercises

Find the PID of a running process and stop it gracefully. Enable and start a service on boot.

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3. Manage Scheduled Jobs

Learn

Cron jobs: user (crontab) andSync system (/etc/cron*). At jobs for one-time scheduling.

Commands

# List user cron jobs
crontab -l

# Edit user cron jobs
crontab -e

# At job example
echo "touch /tmp/testfile" | at now + 1 minute
atq       # list scheduled at jobs
atrm <job_number>

Exercises

Schedule a job to run a script every day at 3am. Schedule a one-time task using atchrony.

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4. Software Management

Learn

Install, update, validate packages using native package manager. Repositories and dependency management.

Commands

# Debian/Ubuntu
sudo apt update
sudo apt install <package>
dpkg -l | grep <package>

# RHEL/CentOS
sudo yum install <package>
rpm -qa | grep <package>

Exercises

Install curl and verify it is installed. Remove a package and confirm removal.

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5. Recover from Hardware, OS, or Filesystem Failures

Learn

Boot into rescue/recovery mode. Use Live CD/USB for repair. Basic filesystem check: fsck.

Commands

sudo fsck /dev/sdX1
sudo mount /dev/sdX1 /mnt

Exercises

Simulate a corrupted filesystem on a test partition and repair it. Boot into rescue mode and inspect disk partitions.

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6. Virtual Machines (libvirt)

Learn

Install and manage VMs using libvirt and virsh.

Commands

virsh list --all
virsh start <vm>
virsh shutdown <vm>
virsh destroy <vm>   # force shutdown
virsh console <vm>

Exercises

Create a VM using virt-installntpd. Start, stop,Check and connectupdate totime the VM via console.

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7. Containers (Docker / Podman)

Learn

Create, start, stop, and manage containers. Understand container networking and volumes.

Commands

# Run container
docker run -it --name mycontainer ubuntu bash

# List running containers
docker ps

# Stop and remove container
docker stop mycontainer
docker rm mycontainer

# List images
docker images

Exercises

Create an Ubuntu container and install curl inside it. Commit container changes to a new image. Remove the container and image.

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8. SELinux (Mandatory Access Control)

Learn

Enforce, permissive, and disabled modes. Troubleshoot SELinux denials.zone.

Commands

# Check current modetime
sestatustimedatectl

# ChangeSet modetime temporarilyzone
timedatectl set-timezone Europe/Paris

# Sync time using chrony
sudo setenforcesystemctl 0start #chronyd
permissivechronyc sudotracking
setenforcechronyc 1   # enforcing

# Check SELinux logs
ausearch -m avcsources

Exercises

1. SwitchConfigure SELinuxNTP tosynchronization permissivewith modea andpublic verify.server.
2. TriggerVerify antime SELinuxsync denial (e.g., wrong file context) and check logs.status.

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Exam3. TipsMonitor & Troubleshoot Networking

Learn

• PracticeUse all commands without root shortcuts (sudo)tools to simulatecheck examconnectivity conditions.and troubleshoot issues.

Commands

ping <host>
traceroute <host>
ss -tulnp  # check listening ports
netstat -rn  # routing table
curl -I http://example.com

Exercises

Ping a remote host and check for packet loss. UnderstandCheck runtimewhich vsservice persistentis changeslistening (kernel,on SELinux,port services)80.

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4. OpenSSH Configuration

Learn

Configure SSH server and client. Manage keys and permissions.

Commands

# Start and enable SSH server
sudo systemctl start sshd
sudo systemctl enable sshd

# Connect to remote server
ssh user@remote_host

# Generate keys
ssh-keygen -t rsa -b 4096
ssh-copy-id user@remote_host

Exercises

Configure SSH to listen on a non-default port. Set up key-based authentication.

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5. Packet Filtering, Port Redirection, NAT

Learn

Configure firewall using iptables or firewalld. UsePerform lab VMs to experiment with containers, VMs,NAT and cronport jobs.forwarding.

Commands

# Check firewall status
sudo firewall-cmd --state

# Allow port 22
sudo firewall-cmd --add-port=22/tcp --permanent
sudo firewall-cmd --reload

# Example NAT rule
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Exercises

Open a specific port on the firewall. Configure port forwarding for SSH.

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6. Static Routing

Learn

Add static routes for traffic control.

Commands

# Add a static route
sudo ip route add 192.168.2.0/24 via 192.168.1.1 dev eth0

# Show routes
ip route show

Exercises

Add a static route to reach a remote network. Verify connectivity via the static route.

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7. Bridge & Bonding Devices

Learn

Network bridging (e.g., for VMs). Bonding for link aggregation.

Commands

# Create bridge
sudo nmcli con add type bridge con-name br0 ifname br0
sudo nmcli con add type bridge-slave con-name eth0-br0 ifname eth0 master br0

# Bonding example
sudo nmcli con add type bond con-name bond0 ifname bond0 mode active-backup
sudo nmcli con add type bond-slave con-name eth1-bond0 ifname eth1 master bond0

Exercises

Create a network bridge and attach an interface. Configure a bonded interface with two NICs.

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8. Reverse Proxies & Load Balancers

Learn

Basics of reverse proxy (e.g., Nginx) and load balancing.

Commands

# Nginx reverse proxy example
sudo nano /etc/nginx/conf.d/reverse.conf
# server { listen 80; location / { proxy_pass http://backend:8080; } }
sudo systemctl reload nginx

Exercises

Configure Nginx to proxy requests to a backend server. Set up basic round-robin load balancing using Nginx.