Networking with Bash: Intermediate & Advanced Commands

Module 1: Network Configuration & Basic Commands

Learning Objectives

Manipulate IP addresses and routes
Perform basic network diagnostics

Key Commands

ip addr show - Show network interfaces
ip route - Display routing table
ip link set eth0 down - Disable interface
ping -c 4 8.8.8.8 - Test connectivity
traceroute 8.8.8.8 - Trace network path
netstat -tuplen - Show network connections
arp -a - View ARP table

Exercise 1

Display all active network interfaces
Create a new static IP configuration for eth1
Test connectivity to Google DNS
Trace route to example.com

Module 2: Firewall Management

Learning Objectives

Create firewall rules using iptables
Use advanced filtering techniques

Key Commands

iptables -L -n -v - List rules
iptables -A INPUT -p tcp --dport 22 -j ACCEPT - Allow SSH
iptables -A FORWARD -s 192.168.1.0/24 -j DROP - Block subnet
iptables-save > /etc/iptables/rules.v4 - Save rules
nft add rule inet filter input tcp dport 80 accept - Nftables example

Exercise 2

Create rule to allow HTTP/HTTPS traffic
Block incoming RDP connections
Save and test firewall configuration

Module 3: DNS Diagnostics

Learning Objectives

Query DNS records
Check domain resolution

Key Commands

dig +short MX example.com - MX record lookup
nslookup -type=AAAA example.com - IPv6 lookup
host -a example.com - Full DNS record dump
drill -T 1.1.1.1 example.com - Use Cloudflare DNS

Exercise 3

Check A record for your domain
Verify SPF record configuration
Compare DNS responses from different servers

Module 4: Advanced Traffic Analysis

Learning Objectives

Capture and analyze network traffic
Use advanced packet filtering

Key Commands

tcpdump -i any port 80 -w capture.pcap - Capture HTTP traffic
tcpdump -nnXSs 0 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420' - Filter GET requests
netcat -l -p 8080 - Create simple server
tc qdisc add dev eth0 root netem delay 100ms - Introduce latency
ss -antp | grep ':80' - List established connections

Exercise 4

Capture and analyze HTTP traffic
Simulate network latency conditions
Check active connections to web server

Module 5: Scripting & Automation

Learning Objectives

Create network automation scripts
Use advanced shell scripting techniques

Key Commands

while true; do ping -c 1 8.8.8.8; sleep 5; done - Simple monitoring
curl -s 'https://api.ipify.org' | grep -q '192.168' || echo "IP Changed" - Conditional check
expect -c 'spawn ssh user@host; expect \"password:\"; send \"pass\r\"' - Automated login
awk '{print $1}' /etc/passwd | sort | uniq -d - Find duplicate usernames
grep -r --include="*.log" "ERROR" /var/log/ - Recursive log search

Exercise 5

Create script to monitor multiple IPs
Write DNS health-check script
Automate firewall rule deployment

Conclusion

These modules cover essential networking tasks using advanced Bash commands. Practice by:

Experimenting with different command options
Modifying examples to fit real-world scenarios
Combining commands into automation scripts

References