Introduction to DNS on Linux

The Domain Name System (DNS) is the backbone of internet connectivity, translating human-readable domain names into IP addresses. In this comprehensive guide, we’ll explore DNS server configuration on Linux systems, focusing on BIND9, the most widely used DNS software.

Installing and Configuring BIND9

Installation

sudo apt update
sudo apt install bind9 bind9-utils bind9-doc

Basic Configuration

1. Edit the main configuration file:

sudo nano /etc/bind/named.conf.local

2. Add a forward zone:

zone "example.com" {
    type master;
    file "/etc/bind/db.example.com";
    allow-transfer { 192.168.1.2; };
    also-notify { 192.168.1.2; };
};

3. Create the zone file:

sudo cp /etc/bind/db.local /etc/bind/db.example.com
sudo nano /etc/bind/db.example.com

Advanced DNS Features

DNSSEC Implementation

1. Generate keys:

sudo dnssec-keygen -a NSEC3RSASHA1 -b 2048 -n ZONE example.com

2. Sign the zone:

sudo dnssec-signzone -A -3 $(head -c 1000 /dev/random | sha1sum | cut -b 1-16) \
    -N INCREMENT -o example.com -t db.example.com

Caching and Performance Optimization

options {
    max-cache-size 512M;
    max-cache-ttl 3600;
    min-cache-ttl 300;
    prefetch 10 60;
};

Troubleshooting and Maintenance

Common Issues and Solutions

• DNS resolution failures: Check with dig +trace example.com
• Configuration errors: Validate with named-checkconf
• Zone transfer problems: Verify with dig axfr @ns1.example.com example.com

Monitoring and Logging

sudo rndc querylog
sudo tail -f /var/log/syslog | grep named

Security Best Practices

1. Run BIND in a chroot jail
2. Implement rate limiting
3. Use TSIG for zone transfers
4. Regularly update BIND

Conclusion

Proper DNS configuration is essential for network reliability and security. By following this guide, you’ll have a robust DNS infrastructure that can handle modern network demands while maintaining security and performance.

Introduction to iproute2

iproute2 is the modern networking toolkit for Linux, replacing traditional tools like ifconfig and route with more powerful and flexible alternatives.

Basic Network Configuration

Interface Management

1. Show interfaces:

ip addr show

2. Add IP address:

sudo ip addr add 192.168.1.100/24 dev eth0

3. Bring interface up:

sudo ip link set eth0 up

Advanced Routing

Routing Tables

1. Add route:

sudo ip route add 10.0.0.0/8 via 192.168.1.1

2. Policy routing:

sudo ip rule add from 192.168.1.100 lookup 100
sudo ip route add default via 192.168.1.1 table 100

Traffic Control

Quality of Service (QoS)

1. Create HTB queue:

sudo tc qdisc add dev eth0 root handle 1: htb

2. Add class:

sudo tc class add dev eth0 parent 1: classid 1:1 htb rate 100mbit

Troubleshooting

1. Network statistics:

nstat -a

2. Socket information:

ss -tulpn

3. Routing diagnostics:

ip route get 8.8.8.8

Performance Optimization

1. TCP tuning:

sudo sysctl -w net.core.rmem_max=16777216
sudo sysctl -w net.core.wmem_max=16777216

2. Interface buffering:

sudo ethtool -G eth0 rx 4096 tx 4096

Conclusion

iproute2 provides powerful tools for network configuration and troubleshooting, making it an essential skill for Linux system administrators.

Learn basic IPTables configuration for Linux firewalls.

1. List current rules:

sudo iptables -L -v -n

2. Allow SSH:

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

3. Block IP:

sudo iptables -A INPUT -s 192.168.1.100 -j DROP

4. Save rules:

sudo iptables-save > /etc/iptables/rules.v4

Read more: IPTables Documentation

Learn how to set up Nginx web server on Linux.

1. Install Nginx:

sudo apt install nginx

2. Start Nginx:

sudo systemctl start nginx

3. Check status:

sudo systemctl status nginx

4. Test configuration:

sudo nginx -t

Read more: Nginx Documentation

Learn how to set up and manage UFW (Uncomplicated Firewall) on Ubuntu with advanced configurations.

1. Install UFW:

sudo apt install ufw

2. Set default policies:

sudo ufw default deny incoming
sudo ufw default allow outgoing

3. Enable UFW:

sudo ufw enable

4. Allow specific services:

sudo ufw allow ssh
sudo ufw allow http
sudo ufw allow https

5. Advanced configurations:

# Allow specific IP range
sudo ufw allow from 192.168.1.0/24

# Rate limiting
sudo ufw limit ssh

# Delete rule
sudo ufw delete allow http

Monitoring and logging:

Learn how to set up secure SSH access on your Linux server with advanced configuration options.

1. Install OpenSSH server:

sudo apt install openssh-server

2. Configure SSH with enhanced security:

sudo nano /etc/ssh/sshd_config

Set these recommended options:

PermitRootLogin no
PasswordAuthentication no
AllowUsers yourusername

3. Generate SSH keys:

ssh-keygen -t ed25519 -C "[email protected]"

4. Restart SSH service:

sudo systemctl restart ssh

5. Test connection with key-based authentication:

ssh -i ~/.ssh/id_ed25519 user@your-server-ip

Additional security measures: