cli.wiki

Network Diagnostics (Layers 1-7)

Dec 30, 20248 min read

Layer 1 (Physical Layer) Diagnostics

Cable and Physical Connection Testing

# Network Interface Status
# macOS
system_profiler SPNetworkDataType | grep "Link Speed"
networksetup -getmedia <interface>
 
# Linux
ethtool <interface> | grep "Speed|Link"
mii-tool <interface>

Signal Quality and Error Detection

# Check interface errors
# Both OS
netstat -i
ifconfig <interface> | grep "errors|dropped|collisions"
 
# Linux specific
ethtool -S <interface>  # Detailed interface statistics

Physical Layer Monitoring Tools

# Linux
ethtool --statistics <interface>
ethtool --register-dump <interface>  # Raw register data
 
# Check for CRC errors
ifconfig <interface> | grep "CRC"

WiFi Signal Diagnostics

# macOS
/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I
airport -s  # Scan available networks
 
# Linux
iwconfig
iwlist <interface> scanning
iw dev <interface> station dump  # Detailed wifi statistics

Interface Status and Configuration

# macOS
ifconfig
networksetup -listallhardwareports
system_profiler SPNetworkDataType
 
# Linux
ip link show
ethtool <interface>
mii-tool <interface>

MAC Address and ARP

# View MAC address table
arp -a   # Both OS
 
# Clear ARP cache
# macOS
sudo arp -d -a
# Linux
sudo ip neigh flush all
 
# Watch ARP traffic
tcpdump -n arp

VLAN Diagnostics

# Linux
ip link add link eth0 name eth0.100 type vlan id 100
vconfig show
 
# macOS
vlan show

Layer 3 (Network Layer) Diagnostics

IPv4 Connectivity

# Basic connectivity
ping <host>
ping -c 4 <host>    # Limited count
 
# Path MTU Discovery
ping -D -s 1472 <host>    # macOS
ping -M do -s 1472 <host> # Linux
 
# Advanced ping options
ping -f <host>      # Flood ping (requires root)
ping -i 0.2 <host>  # Fast interval

IPv6 Connectivity

# Basic IPv6 ping
ping6 <ipv6_host>
ping -6 <ipv6_host>
 
# Link-local address test
ping6 fe80::<interface>
 
# IPv6 neighbor discovery
nd6 -n               # macOS
ip -6 neighbor show  # Linux

Routing

# Show routing table
netstat -rn
route -n
ip route show    # Linux
 
# IPv6 routes
netstat -rn -f inet6
ip -6 route show     # Linux
 
# Trace route
traceroute <host>    # IPv4
traceroute6 <host>   # IPv6
mtr <host>          # Continuous trace

Network Services Diagnostics

DNS

# DNS lookup
dig <domain>
nslookup <domain>
host <domain>
 
# Reverse DNS
dig -x <ip_address>
 
# DNS server test
dig @8.8.8.8 <domain>
 
# Clear DNS cache
# macOS
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
# Linux
sudo systemd-resolve --flush-caches

DHCP

# Release DHCP lease
# macOS
sudo ipconfig set <interface> DHCP
# Linux
sudo dhclient -r <interface>
 
# Request new lease
# macOS
sudo ipconfig set <interface> BOOTP
sudo ipconfig set <interface> DHCP
# Linux
sudo dhclient <interface>

Network Performance Testing

Bandwidth Testing

# Using iperf3
iperf3 -s              # Server mode
iperf3 -c <server_ip>  # Client mode
 
# Basic speed test
speedtest-cli

Socket Statistics

# Open connections
netstat -an
ss -tuln    # Linux
 
# Connection statistics
netstat -s

Advanced Diagnostics

Packet Capture

# Basic capture
tcpdump -i <interface>
 
# Capture with filters
tcpdump -i <interface> host <ip>
tcpdump -i <interface> port 80
 
# Save capture
tcpdump -i <interface> -w capture.pcap

Network Load

# Interface statistics
netstat -i
ip -s link show
 
# Real-time bandwidth monitoring
iftop
nload

SSL/TLS Diagnostics

# Test SSL connection
openssl s_client -connect host:443
 
# Check certificate
openssl x509 -in cert.pem -text

System Network Configuration

Network Services Status

# macOS
sudo launchctl list | grep network
networksetup -listallnetworkservices
 
# Linux
systemctl status network
systemctl status NetworkManager

Firewall Diagnostics

# macOS
sudo pfctl -sa
sudo pfctl -sr
 
# Linux
sudo iptables -L
sudo nft list ruleset

Network Quality Tests

# macOS
networkQuality    # Built-in tool in newer versions
 
# Both OS
mtr <host>       # Network path analysis
curl -o /dev/null http://speedtest.net/mini -w "%{time_total}\n"   # Basic latency test

Common Issues Resolution

# Reset entire network stack macOS
sudo ifconfig <interface> down
sudo route flush
sudo ifconfig <interface> up
 
# Linux
sudo systemctl restart NetworkManager
sudo netplan apply    # Ubuntu

Layer 4 (Transport Layer) Diagnostics

TCP Connection Analysis

# Active TCP connections
netstat -tnp
ss -tnp  # Linux, more detailed
 
# TCP connection states
netstat -ant | awk '{print $6}' | sort | uniq -c
 
# Detailed TCP statistics
netstat -st  # Both OS
cat /proc/net/tcp  # Linux

TCP Connection Testing

# Test specific port
nc -zv host port
telnet host port
 
# TCP connection tracking (Linux)
conntrack -L
ss -t -a

UDP Diagnostics

# Show UDP sockets
netstat -unp
ss -unp  # Linux
 
# UDP port testing
nc -zu host port
 
# Monitor UDP traffic
tcpdump udp

Socket Statistics

# Detailed socket stats
# macOS
netstat -av
lsof -i
 
# Linux
ss -s  # Summary statistics
ss -m  # Memory usage

Performance Testing

# TCP Window Size
sysctl net.inet.tcp.window_size  # macOS
sysctl net.ipv4.tcp_window_scaling  # Linux
 
# Connection Latency
hping3 -S -p 80 host  # TCP SYN timing

Layer 5 (Session Layer) Diagnostics

Session Management

# Active sessions
who
w
last
 
# SSH Sessions
who | grep pts

Application Session Testing

# Test SSL/TLS sessions
openssl s_client -connect host:443 -state
openssl s_client -connect host:443 -debug
 
# Session timeout testing
curl -v --max-time 10 https://host

Session Protocol Analysis

# Monitor session establishment
tcpdump -i any 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0'
 
# Track session state changes
tcpdump -i any 'tcp[tcpflags] & (tcp-syn|tcp-fin|tcp-rst) != 0'

Cross-Layer Analysis Tools

Network Protocol Analyzer

# Wireshark CLI (tshark)
tshark -i <interface>
tshark -i <interface> -f "port 80 or port 443"
 
# Advanced filtering
tshark -i <interface> -Y "tcp.flags.syn==1"

Connection Flow Analysis

# netflow analysis (if installed)
nfdump -R /path/to/flows
fprobe <interface>
 
# Connection tracking
conntrack -L
conntrack -E  # Event monitoring

Advanced Diagnostics

Hardware Diagnostics

# PCI Network Device Info
lspci -vv | grep -A 10 Network
system_profiler SPNetworkDataType  # macOS
 
# Driver Information
ethtool -i <interface>
kextstat | grep -i network  # macOS

Protocol-Specific Tools

# SSL/TLS Analysis
ssldump -i <interface>
sslscan host:port
 
# TCP Dump with Session Context
tcpdump -i <interface> -s 0 -w capture.pcap

Performance Optimization

# TCP Optimization
sysctl -w net.ipv4.tcp_window_scaling=1
sysctl -w net.ipv4.tcp_timestamps=1
 
# Session Optimization
sysctl -w net.ipv4.tcp_max_syn_backlog=4096

Layer 6 (Presentation Layer) Diagnostics

Data Encoding/Decoding

# Character Set Analysis
file -i <filename>
chardet <filename>
 
# Text Encoding Conversion
iconv -f UTF-8 -t ASCII file.txt
iconv -l  # List available encodings

Compression Testing

# Test compression algorithms
gzip -t file.gz
bzip2 -t file.bz2
 
# Check compression ratio
gzip -l file.gz

Encryption Diagnostics

# SSL/TLS Certificate Analysis
openssl x509 -in cert.pem -text -noout
openssl verify cert.pem
 
# Check SSL/TLS Configuration
openssl s_client -connect host:443 -tls1_2
nmap --script ssl-enum-ciphers -p 443 host

MIME Type Analysis

# Check MIME types
file --mime-type file
mimetype file    # Linux
 
# HTTP Content-Type checking
curl -I https://example.com

Layer 7 (Application Layer) Diagnostics

HTTP/HTTPS Diagnostics

# Basic HTTP testing
curl -v https://example.com
wget --debug https://example.com
 
# HTTP headers
curl -I https://example.com
curl -D - https://example.com
 
# HTTP performance
curl -w "\
    time_namelookup:  %{time_namelookup}\n\
    time_connect:  %{time_connect}\n\
    time_appconnect:  %{time_appconnect}\n\
    time_pretransfer:  %{time_pretransfer}\n\
    time_redirect:  %{time_redirect}\n\
    time_starttransfer:  %{time_starttransfer}\n\
    ----------\n\
    time_total:  %{time_total}\n" \
    -o /dev/null -s https://example.com

DNS Diagnostics

# DNS lookup tools
dig +trace domain.com
host -a domain.com
nslookup -debug domain.com
 
# DNS zone transfer
dig @nameserver domain.com AXFR
 
# DNS propagation
dig domain.com @8.8.8.8
dig domain.com @1.1.1.1
 
# DNS record types
dig domain.com ANY
dig domain.com MX
dig domain.com TXT

Email Protocol Testing

# SMTP testing
telnet mail-server 25
nc -v mail-server 25
 
# Test email sending
swaks --to [email protected] --from [email protected]
 
# Check mail server records
dig domain.com MX
dig domain.com TXT    # SPF records

Web Application Testing

# Load testing
ab -n 1000 -c 10 https://example.com/
siege -c 10 -t 30S https://example.com/
 
# Response codes
curl -o /dev/null -s -w "%{http_code}\n" https://example.com/
 
# Content verification
curl -s https://example.com/ | grep "expected_text"

Application Performance Monitoring

# Response time monitoring
httping -c 10 example.com
 
# Server response headers
curl -s -D - example.com -o /dev/null
 
# TLS handshake timing
curl -w "TLS handshake: %{time_appconnect}\n" -o /dev/null -s https://example.com

Protocol-Specific Diagnostics

FTP Testing

# FTP connection test
ftp -n server <<EOF
quote USER username
quote PASS password
quit
EOF
 
# FTP through curl
curl -v ftp://server/

Database Connection Testing

# MySQL
mysqladmin ping -h hostname
mysqlcheck -h hostname -u user -p
 
# PostgreSQL
pg_isready -h hostname
psql -h hostname -p 5432 -U username -c "\l"

API Testing

# REST API testing
curl -X GET "https://api.example.com/endpoint" \
  -H "Authorization: Bearer token"
 
# API response timing
curl -w "@curl-format.txt" -o /dev/null -s "https://api.example.com"

Application Layer Security

Web Security Testing

# SSL/TLS security check
ssllabs-scan example.com
testssl.sh example.com
 
# HTTP security headers
curl -s -D - https://example.com | grep -i "security"

Application Firewall Testing

# WAF detection
wafw00f https://example.com
 
# Basic security scanning
nikto -h https://example.com

Troubleshooting Tools

Application Layer Protocol Analysis

# HTTP traffic analysis
tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
 
# HTTPS traffic (requires key)
ssldump -i any -k keyfile.pem

Service Discovery

# Network service scanning
nmap -sV -p- host
nmap -sC -sV host
 
# Service version detection
nc -zv host port

Performance Analysis

Load Testing Tools

# HTTP load testing
wrk -t12 -c400 -d30s https://example.com
hey -n 1000 -c 100 https://example.com
 
# Concurrent connections
apache2-utils
ab -c 100 -n 1000 https://example.com/

Monitoring Tools

# Real-time HTTP traffic
httpry -i eth0
tcpflow -i eth0 -c port 80
 
# Application logs analysis
tail -f /var/log/apache2/access.log | goaccess

Graph View

Backlinks

  • No backlinks found