🌐 Introduction to Linux and Networking Tools¶
Author: Dr. Kaikai Liu, Ph.D.
Position: Associate Professor, Computer Engineering
Institution: San Jose State University
Contact: kaikai.liu@sjsu.edu
🧠 Part 1: Basic Computer Networking Concepts¶
Before using tools, it's essential to understand the fundamental components of computer networks:
📡 Key Concepts¶
| Concept | Description |
|---|---|
| IP Address | Unique identifier for a device on a network (e.g., 192.168.1.10) |
| Subnet | Logical subdivision of a network |
| Gateway | Device that routes traffic to other networks |
| DNS | Domain Name System — translates domain names into IP addresses |
| MAC Address | Hardware address of a network interface |
| DHCP | Automatically assigns IP addresses on a network |
| NAT | Network Address Translation — allows multiple devices to share one IP |
| Port | Logical access channel for communication (e.g., port 22 = SSH) |
🔀 Network Types¶
- LAN (Local Area Network): Limited to a building or campus
- WAN (Wide Area Network): Broader networks like the internet
- Switch: Connects devices within LAN
- Router: Connects LAN to WAN
🧩 Part 2: The 5 Layers of Computer Networking (Simplified TCP/IP Model)¶
Computer networking is typically divided into 5 abstract layers, each with specific responsibilities and headers:
| Layer | Purpose | Example Protocols | Header Example |
|---|---|---|---|
| Application | Interface for user applications | HTTP, SSH, DNS, FTP | HTTP headers, DNS records |
| Transport | Ensures reliable communication, manages ports | TCP, UDP | TCP/UDP header (port #s) |
| Network | Routing and addressing between networks | IP, ICMP | IP header (IP address) |
| Data Link | Direct link communication on local network | Ethernet, Wi-Fi (802.11) | MAC header |
| Physical | Transmission of bits over physical medium | Cables, Wi-Fi radios | Voltage/pulse or RF wave |
🛠️ Linux Implementation of Each Layer¶
| Layer | Linux Tools / Files | Kernel/Driver Components |
|---|---|---|
| Application | curl, wget, ssh, scp | User space tools |
| Transport | ss, netstat, iptables | TCP/UDP stacks in kernel (net/ipv4) |
| Network | ip, ifconfig, traceroute, ip rule | IP routing tables, netfilter |
| Data Link | ethtool, iw, nmcli | Network driver, MAC layer |
| Physical | rfkill, iwconfig, hciconfig | Wi-Fi/Bluetooth chip drivers |
🧪 Network Discovery and Performance Testing¶
All network packages used in this section are arealdy installed in the container. Run the following commands to start the default container:
sjsujetsontool shell
Check Interfaces and IP Address
Install net-tools (Debian/Ubuntu-based)
#apt install -y net-tools #already installed in the container, This will install: ifconfig, netstat, route, arp, etc.
ifconfig
Modern Linux systems prefer ip command from iproute2:
#apt install -y iproute2 #already installed in the container
ip a
ip addr
ip link
🌐 Discover Devices on LAN¶
nmap -sn 192.168.1.0/24
📊 Measure Speed and Latency¶
iperf3 — Network Bandwidth Testing¶
# On one device (server):
iperf3 -s
# On another device (client):
iperf3 -c <server-ip>
ping — Latency Test¶
#apt install -y iputils-ping
ping google.com
speedtest-cli — Internet Speed Test¶
#sudo apt install speedtest-cli #already installed in the container
root@sjsujetson-01:/Developer# speedtest-cli
🧰 Part 3: Linux Networking Tools Summary
| Tool | Purpose |
|---|---|
ip |
IP and interface management |
ping |
Test connectivity |
ss |
Check open ports/sockets |
nmap |
Network discovery and scanning |
ufw |
Basic firewall management |
curl/wget |
Web requests and file download |
nmcli |
Network connection and Wi-Fi control |
bluetoothctl |
Bluetooth device scanning and pairing |
iperf3 |
Network throughput measurement |
speedtest-cli |
Measure Internet bandwidth and latency |
📶 Wi-Fi and Bluetooth Networking¶
Jetson supports both Wi-Fi and Bluetooth, often via M.2 cards or USB dongles.
📡 Wi-Fi Management Tools¶
nmcli device wifi list # Scan for Wi-Fi networks
nmcli device wifi connect <SSID> password <password>
iwconfig # View wireless settings (deprecated)
🔵 Bluetooth Tools¶
bluetoothctl # Interactive Bluetooth manager
rfkill list # Check if Bluetooth/Wi-Fi are blocked
hciconfig # View Bluetooth device configuration
🔬 Advanced Network Protocol Analysis¶
📊 Understanding Network Headers¶
Each layer adds its own header to the data packet. Let's examine how to inspect these headers on Jetson:
🔍 Packet Capture with tcpdump¶
# Install tcpdump if not available
#root@sjsujetson-01:/Developer# apt install tcpdump #already installed inside the container
# Capture packets on specific interface
root@sjsujetson-01:/Developer# tcpdump -i wlP1p1s0 -n -c 10
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on wlP1p1s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
.....
# Capture HTTP traffic
root@sjsujetson-01:/Developer# tcpdump -i any port 80 -A
tcpdump: data link type LINUX_SLL2
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes
.....
# Capture with detailed headers
root@sjsujetson-01:/Developer# tcpdump -i any -v -n icmp
tcpdump: data link type LINUX_SLL2
tcpdump: listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes
🌐 Layer-by-Layer Analysis¶
| Layer | Header Fields | Linux Command to Inspect |
|---|---|---|
| Application | HTTP methods, DNS queries | curl -v, dig, nslookup |
| Transport | Source/Dest ports, TCP flags | ss -tuln, netstat -tuln |
| Network | Source/Dest IP, TTL | ip route, traceroute |
| Data Link | MAC addresses, VLAN tags | ip link, ethtool |
| Physical | Signal strength, channel | iwconfig, iw dev wlan0 scan |
🔧 Protocol-Specific Tools¶
DNS Analysis¶
#These are already installed inside the container
# apt update
# # Install dig and nslookup (part of dnsutils)
# apt install -y dnsutils
# # Install 'time' command (optional, usually pre-installed)
# apt install -y time
# Query DNS records
dig google.com
nslookup google.com
# Check DNS resolution time
time nslookup google.com
# Use specific DNS server
dig @8.8.8.8 google.com
TCP Connection Analysis¶
# Show TCP connection states
ss -tuln
# Monitor TCP connections in real-time
watch -n 1 'ss -tuln | grep :22'
# Check TCP window scaling
ss -i
🛠️ Advanced Linux Network Tools¶
🔍 Network Troubleshooting Arsenal¶
| Tool | Purpose | Example | Installation |
|---|---|---|---|
traceroute |
Trace packet path | traceroute google.com |
sudo apt install traceroute |
mtr |
Continuous traceroute | mtr google.com |
sudo apt install mtr |
netstat |
Network statistics | netstat -rn (routing table) |
sudo apt install net-tools |
lsof |
List open files/sockets | lsof -i :22 (SSH connections) |
sudo apt install lsof |
tcpdump |
Packet capture | sudo tcpdump -i wlan0 |
sudo apt install tcpdump |
wireshark |
GUI packet analyzer | sudo wireshark |
sudo apt install wireshark+ Add user to group: sudo usermod -aG wireshark $USER |
ethtool |
Ethernet tool | ethtool eth0 |
sudo apt install ethtool |
iw |
Wireless tools | iw dev wlan0 info |
sudo apt install iw |
All these tools are already installed inside the container, run
sjsujetsontool shellto enter into the container.
Packet Capture and Basic Analysis
# Terminal 1: Capture all packets across interfaces
root@sjsujetson-01:/Developer# tcpdump -i any -w network_capture.pcap
# Terminal 2: Generate some traffic
ping -c 10 google.com
curl -I https://www.google.com
# Terminal 1: Ctrl+C to stop capture
#CLI analysis
root@sjsujetson-01:/Developer# tcpdump -r network_capture.pcap -n
📡 Wireless Network Deep Dive¶
Wi-Fi Interface Management¶
iw dev
# Detailed wireless info
iw dev wlP1p1s0 info
# Check wireless statistics
cat /proc/net/wireless
Bluetooth Low Energy (BLE) on Jetson¶
# Install Bluetooth tools, already in container
#apt install bluez bluez-tools
# Scan for BLE devices
hcitool lescan
# Get device info
hciconfig hci0
# Monitor Bluetooth traffic
btmon
🔒 Network Security Tools¶
Port Scanning and Security¶
#apt install -y nmap
#Check Open Ports on Jetson
root@sjsujetson-01:/Developer# nmap -sS localhost
Starting Nmap 7.94SVN ( https://nmap.org ) at 2025-07-15 01:49 UTC
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000014s latency).
Not shown: 997 closed tcp ports (reset)
PORT STATE SERVICE
22/tcp open ssh
111/tcp open rpcbind
631/tcp open ipp
# Comprehensive port scan
nmap -sS -O -sV 192.168.1.1
# Scan for vulnerabilities
nmap --script vuln 192.168.1.1
Firewall Management (need host sudo)¶
# UFW (Uncomplicated Firewall)
sudo apt install -y ufw
sudo ufw enable
sudo ufw allow ssh
sudo ufw allow 8080/tcp
sudo ufw status verbose
# iptables (advanced)
sudo iptables -L -n -v
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
📋 Network Layer Analysis¶
Task 1.1: Packet Capture and Analysis¶
In this task, you'll learn how to capture and analyze network traffic using tcpdump.
# Terminal 1 (inside the container): Start packet capture
root@sjsujetson-01:/Developer# tcpdump -i any -w network_capture.pcap
tcpdump: data link type LINUX_SLL2
tcpdump: listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes
# Terminal 2 (inside the container): Generate traffic
root@sjsujetson-01:/workspace# ping -c 10 google.com
root@sjsujetson-01:/workspace# curl -I https://www.google.com
# Stop capture (Ctrl+C in Terminal 1)
# Analyze captured packets
root@sjsujetson-01:/Developer# tcpdump -r network_capture.pcap -n
Task 1.2: Layer-by-Layer Inspection¶
This task demonstrates how to inspect network traffic at different OSI model layers.
# Physical layer - Wi-Fi signal (not permitted in Jetson)
# iw dev wlP1p1s0 scan | grep -A 5 -B 5 "signal:"
# Data link layer - MAC addresses
ip link show
arp -a
# Network layer - IP routing
ip route show
traceroute 8.8.8.8 # apt install traceroute
# Transport layer - TCP/UDP ports
ss -tuln
lsof -i # run `sudo lsof -i` in host for more detailed output
# Application layer - HTTP headers
curl -v http://httpbin.org/get
Using Wireshark and Tshark¶
Tshark is the command-line version of Wireshark, a powerful network protocol analyzer. Follow these steps to set it up:
- Install Tshark and configure permissions:
apt install -y tshark
root@sjsujetson-00:/workspace# which dumpcap
/usr/bin/dumpcap
root@sjsujetson-00:/workspace# setcap cap_net_raw,cap_net_admin=eip /usr/bin/dumpcap
root@sjsujetson-00:/workspace# getcap /usr/bin/dumpcap
/usr/bin/dumpcap cap_net_admin,cap_net_raw=eip
- Capture packets using Tshark:
root@sjsujetson-00:/workspace# tshark -i wlP1p1s0
- Test X11 window forwarding with a simple application:
apt install -y x11-apps
xeyes
- Install Wireshark with GUI support:
apt update
root@sjsujetson-00:/workspace# DEBIAN_FRONTEND=noninteractive apt install -y wireshark
- Run Wireshark inside the container:
wireshark