Host Discovery (Is the host alive?)

Nerd Cafe | نرد کافه

Why this matters

Before scanning ports, Nmap checks:

“Should I even bother scanning this host?”

Default host discovery

Uses:

• ICMP Echo (ping)

• TCP SYN to port 443

• TCP ACK to port 80

Explicit ping scan

$ nmap -sn scanme.nmap.org

Starting Nmap 7.94 ( https://nmap.org ) at 2026-02-10 20:19 Iran Standard Time
Nmap scan report for scanme.nmap.org (50.7.87.84)
Host is up (0.13s latency).
Other addresses for scanme.nmap.org (not scanned): 50.7.87.86 88.99.249.74 50.7.87.85 204.12.192.218 204.12.192.219 69.197.138.83 50.7.87.82 50.7.87.83 178.63.240.97 50.7.85.222 188.40.181.50 178.63.240.96 69.197.138.82 50.7.85.219 188.40.181.51 50.7.85.218 69.197.146.179 69.197.146.178 188.40.181.48 188.40.181.49 50.7.85.220 50.7.85.221
rDNS record for 50.7.87.84: server.jibrail.com
Nmap done: 1 IP address (1 host up) scanned in 7.76 seconds

Result

• Host is up

• No port scan performed

Skip host discovery (assume host is alive)

$ nmap -Pn scanme.nmap.org

Starting Nmap 7.94 ( https://nmap.org ) at 2026-02-10 20:22 Iran Standard Time
Nmap scan report for scanme.nmap.org (188.40.181.49)
Host is up (0.15s latency).
Other addresses for scanme.nmap.org (not scanned): 50.7.87.83 69.197.138.83 188.40.181.48 50.7.87.86 50.7.87.84 69.197.146.179 188.40.181.50 69.197.146.178 88.99.249.74 69.197.138.82 204.12.192.218 204.12.192.219 50.7.85.222 178.63.240.96 50.7.85.218 50.7.87.82 50.7.85.221 178.63.240.97 50.7.87.85 50.7.85.219 50.7.85.220 188.40.181.51
rDNS record for 188.40.181.49: static.49.181.40.188.clients.your-server.de
Not shown: 989 closed tcp ports (reset)
PORT      STATE SERVICE
22/tcp    open  ssh
80/tcp    open  http
443/tcp   open  https
3333/tcp  open  dec-notes
5810/tcp  open  unknown
7777/tcp  open  cbt
8080/tcp  open  http-proxy
8888/tcp  open  sun-answerbook
9100/tcp  open  jetdirect
9418/tcp  open  git
65000/tcp open  unknown

Nmap done: 1 IP address (1 host up) scanned in 20.98 seconds

Use case

• Host blocks ICMP

• Internal networks

• Firewalled environments

💖 Support Our Work

If you find this post helpful and would like to support my work, you can send a donation via TRC-20 (USDT). Your contributions help us keep creating and sharing more valuable content.

TRC-20 Address: TAAVVf9ZxUpbyvTa6Gd5SGPmctBdy4PQwf

Thank you for your generosity! 🙏

Keywords

Nmap, Red Team, Blue Team, Reconnaissance, Port Scanning, Host Discovery, Service Enumeration, OS Fingerprinting, NSE Scripts, SYN Scan, IDS Detection, SIEM Correlation, Network Telemetry, Firewall Evasion, Timing Templates, Attack Surface, Defensive Monitoring, Incident Response, Purple Teaming, MITRE ATT&CK, nerd cafe , نرد کافه

Channel Overview

🌐 Website: www.nerd-cafe.ir

📺 YouTube: @nerd-cafe

🎥 Aparat: nerd_cafe

📌 Pinterest: nerd_cafe

📱 Telegram: @nerd_cafe

📝 Blog: Nerd Café on Virgool

💻 GitHub: nerd-cafe