Network Troubleshooting

19. 08. 2025 1 min read intermediate

Bottom-up¶

Fyzická (kabel, link) → 2. L2 (ARP, MAC) → 3. L3 (IP, routing, ping) → 4. L4 (TCP/UDP, porty) → 5. L7 (DNS, HTTP, TLS)

Commands¶

ping -c 4 8.8.8.8 mtr -r google.com dig example.com ss -tlnp nc -zv server 80 curl -v https://example.com openssl s_client -connect example.com:443 tcpdump -i any port 80 -nn

Běžné problémy¶

DNS failure → dig @8.8.8.8, resolv.conf
Connection refused → služba neběží, firewall
Connection timeout → routing, firewall, host down
SSL chyba → certifikát, hostname
Intermittent → MTU, packet loss (mtr)

Systematicky L1 → L7¶

Ping, traceroute, dig, curl — vyřeší 90 % problémů.

troubleshootingnetworkingdiagnostika

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