Linux Networking

# List listening TCP/UDP ports
ss -tuln

# Show established connections with process
ss -tup

# List all listening ports
netstat -tulnp

# Show routing table
netstat -rn

# Capture traffic to port 443
tcpdump -i eth0 port 443

# Capture DNS traffic
tcpdump -i eth0 udp port 53

ping -c 5 api.example.com
traceroute api.example.com

# Filter by port
ss -tuln sport = :443

# Filter by process
ss -tup | grep nginx

# Show routes
ip route

# Show interfaces
ip link show

# Capture traffic to a host and port
tcpdump -i eth0 host 10.0.0.5 and port 5432

# List rules
nft list ruleset

# List tables and chains
nft list tables
nft list chains

# Test TCP connectivity
nc -vz example.com 443

# Listen on a TCP port
nc -l 0.0.0.0 9000

# UDP test
nc -u -vz example.com 53