Troubleshooting jaringan adalah skill esensial untuk sysadmin dan developer. Linux menyediakan berbagai tools command line yang powerful untuk diagnose masalah network. Artikel ini membahas penggunaan ping, netstat, nmap, dan tools troubleshooting lainnya secara comprehensive.

Basic Connectivity Test

1. Ping Command

Ping adalah tool paling dasar untuk test connectivity.

# Ping ke host/domain
ping google.com
Ping dengan count spesifik
ping -c 4 google.com
Ping dengan interval
ping -i 2 google.com    # Setiap 2 detik
Ping dengan timeout
ping -w 10 google.com   # Stop setelah 10 detik
Ping dengan packet size
ping -s 1024 google.com
Flood ping (root only)
sudo ping -f localhost
Audible ping (bunyi beep saat reply)
ping -a google.com

2. Traceroute

Traceroute melacak route yang dilalui packets.

# Basic traceroute
traceroute google.com
Traceroute dengan ICMP (bukan UDP)
traceroute -I google.com
Traceroute dengan TCP port
traceroute -T -p 443 google.com
Limit hops
traceroute -m 15 google.com
Atau gunakan tracepath
tracepath google.com

3. MTR (My Traceroute)

MTR menggabungkan ping dan traceroute.

# Install mtr
sudo apt install mtr    # Debian/Ubuntu
sudo dnf install mtr    # Fedora
Run mtr
mtr google.com
MTR dengan report mode
mtr --report --report-cycles 10 google.com
MTR dengan TCP
traceroute -T google.com

Network Interface Tools

4. ifconfig / ip

# List interfaces (modern)
ip addr show
Atau dengan ifconfig (legacy)
ifconfig
Detail interface spesifik
ip addr show eth0
Statistik interface
ip -s link show eth0
Enable/disable interface
sudo ip link set eth0 up
sudo ip link set eth0 down
Set IP address
sudo ip addr add 192.168.1.100/24 dev eth0
sudo ip addr del 192.168.1.100/24 dev eth0
Flush IP addresses
sudo ip addr flush dev eth0

5. ethtool

# Install
sudo apt install ethtool
Cek link status
sudo ethtool eth0
Cek statistics
sudo ethtool -S eth0
Test cable
sudo ethtool -t eth0
Set speed dan duplex
sudo ethtool -s eth0 speed 1000 duplex full autoneg off

Network Connection Tools

6. netstat

# List semua connections
netstat -a
List TCP connections
netstat -at
List UDP connections
netstat -au
List listening ports
netstat -tulpn
List dengan PID
sudo netstat -tulpn | grep :80
Statistics
netstat -s
Routing table
netstat -r
atau:
route -n
Interface statistics
netstat -i

7. ss (Socket Statistics) – Modern Alternative

# List all sockets
ss -a
List TCP sockets
ss -t -a
List UDP sockets
ss -u -a
List listening sockets
ss -tlnp
List dengan process
ss -tlnp | grep :80
Summary
ss -s
Filter by state
ss -t state established
Filter by connection to specific port
ss -t dst :443
Show timer info
ss -t -o

8. lsof (List Open Files)

# List network connections
sudo lsof -i
List TCP
sudo lsof -i TCP
List specific port
sudo lsof -i :80
sudo lsof -i :443
List listening ports
sudo lsof -i -P -n | grep LISTEN
List connections by process
sudo lsof -i -P -n | grep nginx
List IPv4/IPv6 only
sudo lsof -i 4
sudo lsof -i 6

Port Scanning dan Discovery

9. Nmap

Nmap adalah network scanner yang powerful.

# Install
sudo apt install nmap
Scan single host
nmap 192.168.1.1
Scan multiple hosts
nmap 192.168.1.1 192.168.1.2
Scan range
nmap 192.168.1.1-254
Scan subnet
nmap 192.168.1.0/24
Scan dengan port range
nmap -p 1-65535 192.168.1.1
Scan specific ports
nmap -p 22,80,443 192.168.1.1
Scan dengan service detection
nmap -sV 192.168.1.1
OS detection
sudo nmap -O 192.168.1.1
Aggressive scan
sudo nmap -A 192.168.1.1
Stealth scan
sudo nmap -sS 192.168.1.1
UDP scan
sudo nmap -sU 192.168.1.1
Fast scan (100 ports paling umum)
nmap -F 192.168.1.1
Scan dari file
nmap -iL hosts.txt
Output ke file
nmap -oN scan.txt 192.168.1.1
nmap -oX scan.xml 192.168.1.1
Scan dengan script
nmap --script vuln 192.168.1.1

10. nc (Netcat)

Netcat adalah “Swiss Army Knife” untuk networking.

# Test port connectivity
nc -zv hostname 80
nc -zv google.com 443
Test multiple ports
nc -zv google.com 80 443 8080
Create listener
nc -l 8080
Create reverse shell (hati-hati!)
nc -e /bin/bash -l 8080
Send file
nc -w 3 hostname 8080 < file.txt
Receive file
nc -l 8080 > received_file.txt
Port scan
nc -zv 192.168.1.1 1-1024

DNS Tools

11. nslookup

# Query DNS
nslookup google.com
Query specific record
nslookup -query=MX google.com
nslookup -query=NS google.com
Query specific nameserver
nslookup google.com 8.8.8.8

12. dig

# Basic query
dig google.com
Query specific record
dig google.com MX
dig google.com NS
dig google.com TXT
Query dengan detail
dig +trace google.com
Reverse DNS
dig -x 8.8.8.8
Query specific nameserver
dig @8.8.8.8 google.com
Short output
dig +short google.com
Query semua records
dig google.com ANY

13. host

# Simple DNS lookup
host google.com
Lookup specific type
host -t MX google.com
Reverse lookup
host 8.8.8.8

14. whois

# Install
sudo apt install whois
Lookup domain info
whois google.com
Lookup IP info
whois 8.8.8.8

Advanced Network Tools

15. tcpdump

# Install
sudo apt install tcpdump
Capture semua packets
sudo tcpdump
Capture di interface spesifik
sudo tcpdump -i eth0
Capture dengan filter
sudo tcpdump -i eth0 port 80
sudo tcpdump -i eth0 host 192.168.1.100
sudo tcpdump -i eth0 src 192.168.1.100
sudo tcpdump -i eth0 dst 192.168.1.100
Capture dan save ke file
sudo tcpdump -w capture.pcap
Read dari file
sudo tcpdump -r capture.pcap
Capture dengan verbose
sudo tcpdump -v
sudo tcpdump -vv
sudo tcpdump -vvv
Capture limit
sudo tcpdump -c 100
Capture dengan timestamp
sudo tcpdump -tttt
Filter protocol
sudo tcpdump icmp
sudo tcpdump tcp
sudo tcpdump udp
Complex filter
sudo tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'

16. Wireshark / tshark

# Install
sudo apt install wireshark tshark
Capture dengan tshark
sudo tshark -i eth0
Capture dengan filter
sudo tshark -i eth0 port 80
Capture ke file
sudo tshark -w capture.pcap
Read file
sudo tshark -r capture.pcap

17. nload

# Install
sudo apt install nload
Monitor traffic
sudo nload
Monitor interface spesifik
sudo nload eth0

18. iftop

# Install
sudo apt install iftop
Monitor bandwidth usage
sudo iftop
Monitor interface spesifik
sudo iftop -i eth0
Monitor port spesifik
sudo iftop -f "port 80"

19. bmon

# Install
sudo apt install bmon
Monitor dengan grafik
sudo bmon
Export ke file
sudo bmon -o ascii > bandwidth.log

Routing Tools

20. route / ip route

# Show routing table
ip route show
# atau:
route -n
Add route
sudo ip route add 192.168.2.0/24 via 192.168.1.1
Delete route
sudo ip route del 192.168.2.0/24
Default route
sudo ip route add default via 192.168.1.1
Show specific route
ip route get 8.8.8.8

21. arp

# Show ARP table
ip neigh show
# atau:
arp -a
Delete ARP entry
sudo ip neigh del 192.168.1.100 dev eth0
Flush ARP cache
sudo ip neigh flush all

Firewall Tools

22. iptables

# List rules
sudo iptables -L
sudo iptables -L -v -n
List dengan line numbers
sudo iptables -L --line-numbers
List specific table
sudo iptables -t nat -L
sudo iptables -t mangle -L
Monitor packets
sudo iptables -A INPUT -j LOG
Clear all rules
sudo iptables -F
sudo iptables -X
sudo iptables -t nat -F
sudo iptables -t nat -X

23. nftables

# List ruleset
sudo nft list ruleset
List table spesifik
sudo nft list table inet filter
Monitor
sudo nft monitor

WiFi Tools

24. iw / iwconfig

# List wireless devices
iw dev
Scan networks
sudo iw dev wlan0 scan
Connect (gunakan NetworkManager atau wpa_supplicant untuk full connection)
Show wireless link
iw dev wlan0 link
Legacy: iwconfig
iwconfig
iwconfig wlan0

25. wavemon

# Install
sudo apt install wavemon
Monitor WiFi signal
sudo wavemon

Network Testing Scripts

Script: Complete Network Diagnose

#!/bin/bash
# network-diagnose.sh
HOST="$1"
if [ -z "$HOST" ]; then
echo "Usage: $0 <hostname/IP>"
exit 1
fi
echo "========================================"
echo "Network Diagnose Report for: $HOST"
echo "Date: $(date)"
echo "========================================"
echo -e "\n--- Basic Connectivity ---"
ping -c 4 "$HOST"
echo -e "\n--- Route Trace ---"
traceroute -m 15 "$HOST" 2>/dev/null || tracepath "$HOST" 2>/dev/null
echo -e "\n--- DNS Resolution ---"
dig +short "$HOST"
echo -e "\n--- Port Scan (Top 20) ---"
nmap -F "$HOST" 2>/dev/null || echo "nmap not installed"
echo -e "\n--- Report Complete ---"

Script: Monitor Network Health

#!/bin/bash
# network-monitor.sh
LOGFILE="/var/log/network-health.log"
HOSTS=("8.8.8.8" "1.1.1.1" "google.com")
for host in "${HOSTS[@]}"; do
if ping -c 1 -W 2 "$host" > /dev/null 2>&1; then
echo "[$(date)] $host: UP" >> "$LOGFILE"
else
echo "[$(date)] $host: DOWN" >> "$LOGFILE"
fi
done

Troubleshooting Common Network Issues

1. No Internet Connectivity

# 1. Cek interface
ip addr show
2. Cek gateway
ip route | grep default
3. Test gateway
ping $(ip route | grep default | awk '{print $3}')
4. Test DNS
ping 8.8.8.8
5. Cek DNS resolution
dig google.com
6. Cek resolv.conf
cat /etc/resolv.conf
7. Restart networking
sudo systemctl restart NetworkManager
atau:
sudo systemctl restart networking

2. Slow Network

# 1. Test speed dengan iperf3
sudo apt install iperf3
iperf3 -c iperf.he.net
2. Cek bandwidth usage
sudo iftop -i eth0
3. Cek errors
ip -s link show eth0
4. Test dengan mtr
mtr --report google.com
5. Cek duplex/speed
sudo ethtool eth0

3. Connection Refused

# 1. Cek apakah service running
sudo systemctl status nginx
2. Cek listening ports
sudo ss -tlnp | grep :80
3. Test dengan nc
nc -zv localhost 80
4. Cek firewall
sudo iptables -L | grep 80
sudo ufw status | grep 80
5. Check logs
sudo tail -f /var/log/nginx/error.log

4. DNS Not Working

# 1. Cek resolv.conf
cat /etc/resolv.conf
2. Test dengan dig
dig @8.8.8.8 google.com
3. Cek DNS service
sudo systemctl status systemd-resolved
4. Flush DNS cache
sudo systemd-resolve --flush-caches
5. Test hosts file
ping localhost
cat /etc/hosts

Kesimpulan

Troubleshooting jaringan Linux memerlukan kombinasi tools yang tepat dan pemahaman tentang networking concepts. Dengan menguasai tools di atas, Anda bisa:

1. Diagnose connectivity issues dengan ping, traceroute, mtr
2. Analyze network traffic dengan tcpdump, wireshark
3. Scan dan audit network dengan nmap, nc
4. Monitor performance dengan nload, iftop, bmon
5. Troubleshoot DNS dengan dig, nslookup
6. Manage firewall dengan iptables, nftables

Latihan secara regular dengan scenario troubleshooting untuk mempertajam skill Anda. Network troubleshooting adalah skill yang selalu berguna dalam karir IT apapun.