Networking Security Cheatsheet

Common Ports

Protocol Quick Reference

Nmap Flags (Lab Use)

# Authorized target only
nmap -sV -sC -T4 scanme.nmap.org

Firewall Rules

nftables

nft add table inet filter
nft add chain inet filter input { type filter hook input priority 0 \; policy drop \; }
nft add rule inet filter input ct state established,related accept
nft add rule inet filter input tcp dport {22,443} accept
nft list ruleset

iptables (legacy)

iptables -P INPUT DROP
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
iptables -L -n -v

tcpdump / Wireshark Filters

tcpdump -i eth0 -nn -c 100 'tcp port 443'
tcpdump -i eth0 -w capture.pcap host 10.0.0.5

TLS / Cipher Config

# nginx: TLS 1.2/1.3 only, strong ciphers, HSTS
ssl_protocols TLSv1.2 TLSv1.3;
ssl_prefer_server_ciphers off;
ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
add_header Strict-Transport-Security "max-age=63072000" always;

# Test a server's TLS config
openssl s_client -connect example.com:443 -tls1_3

Subnetting / CIDR