關於 Nmap 的簡單介紹在 Day 6 有提過這邊就不贅述了，直接進入主題，今天打算介紹一下主機發現 Host Discovery。

• Nmap 基本指令架構

nmap <掃描種類> <選項> <目標>

--help 參考指南

CLI 工具最常見的選項 ( 有些工具的說明文件是用 -h ) ，用來列出 Nmap 官方提供的使用說明及選項的簡單介紹。

nmap --help                      
Nmap 7.95 ( https://nmap.org )
Usage: nmap [Scan Type(s)] [Options] {target specification}
TARGET SPECIFICATION:
  Can pass hostnames, IP addresses, networks, etc.
  Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254
  -iL <inputfilename>: Input from list of hosts/networks
  -iR <num hosts>: Choose random targets
  --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
  --excludefile <exclude_file>: Exclude list from file
HOST DISCOVERY:
  -sL: List Scan - simply list targets to scan
  -sn: Ping Scan - disable port scan
  -Pn: Treat all hosts as online -- skip host discovery
  -PS/PA/PU/PY[portlist]: TCP SYN, TCP ACK, UDP or SCTP discovery to given ports
  -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
  -PO[protocol list]: IP Protocol Ping
  -n/-R: Never do DNS resolution/Always resolve [default: sometimes]
  --dns-servers <serv1[,serv2],...>: Specify custom DNS servers
  --system-dns: Use OS's DNS resolver
  --traceroute: Trace hop path to each host
SCAN TECHNIQUES:
  -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
  -sU: UDP Scan
  -sN/sF/sX: TCP Null, FIN, and Xmas scans
  --scanflags <flags>: Customize TCP scan flags
  -sI <zombie host[:probeport]>: Idle scan
  -sY/sZ: SCTP INIT/COOKIE-ECHO scans
  -sO: IP protocol scan
  -b <FTP relay host>: FTP bounce scan
PORT SPECIFICATION AND SCAN ORDER:
  -p <port ranges>: Only scan specified ports
    Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
  --exclude-ports <port ranges>: Exclude the specified ports from scanning
  -F: Fast mode - Scan fewer ports than the default scan
  -r: Scan ports sequentially - don't randomize
  --top-ports <number>: Scan <number> most common ports
  --port-ratio <ratio>: Scan ports more common than <ratio>
SERVICE/VERSION DETECTION:
  -sV: Probe open ports to determine service/version info
  --version-intensity <level>: Set from 0 (light) to 9 (try all probes)
  --version-light: Limit to most likely probes (intensity 2)
  --version-all: Try every single probe (intensity 9)
  --version-trace: Show detailed version scan activity (for debugging)
SCRIPT SCAN:
  -sC: equivalent to --script=default
  --script=<Lua scripts>: <Lua scripts> is a comma separated list of
           directories, script-files or script-categories
  --script-args=<n1=v1,[n2=v2,...]>: provide arguments to scripts
  --script-args-file=filename: provide NSE script args in a file
  --script-trace: Show all data sent and received
  --script-updatedb: Update the script database.
  --script-help=<Lua scripts>: Show help about scripts.
           <Lua scripts> is a comma-separated list of script-files or
           script-categories.
OS DETECTION:
  -O: Enable OS detection
  --osscan-limit: Limit OS detection to promising targets
  --osscan-guess: Guess OS more aggressively
TIMING AND PERFORMANCE:
  Options which take <time> are in seconds, or append 'ms' (milliseconds),
  's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).
  -T<0-5>: Set timing template (higher is faster)
  --min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
  --min-parallelism/max-parallelism <numprobes>: Probe parallelization
  --min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
      probe round trip time.
  --max-retries <tries>: Caps number of port scan probe retransmissions.
  --host-timeout <time>: Give up on target after this long
  --scan-delay/--max-scan-delay <time>: Adjust delay between probes
  --min-rate <number>: Send packets no slower than <number> per second
  --max-rate <number>: Send packets no faster than <number> per second
FIREWALL/IDS EVASION AND SPOOFING:
  -f; --mtu <val>: fragment packets (optionally w/given MTU)
  -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys
  -S <IP_Address>: Spoof source address
  -e <iface>: Use specified interface
  -g/--source-port <portnum>: Use given port number
  --proxies <url1,[url2],...>: Relay connections through HTTP/SOCKS4 proxies
  --data <hex string>: Append a custom payload to sent packets
  --data-string <string>: Append a custom ASCII string to sent packets
  --data-length <num>: Append random data to sent packets
  --ip-options <options>: Send packets with specified ip options
  --ttl <val>: Set IP time-to-live field
  --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
  --badsum: Send packets with a bogus TCP/UDP/SCTP checksum
OUTPUT:
  -oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
     and Grepable format, respectively, to the given filename.
  -oA <basename>: Output in the three major formats at once
  -v: Increase verbosity level (use -vv or more for greater effect)
  -d: Increase debugging level (use -dd or more for greater effect)
  --reason: Display the reason a port is in a particular state
  --open: Only show open (or possibly open) ports
  --packet-trace: Show all packets sent and received
  --iflist: Print host interfaces and routes (for debugging)
  --append-output: Append to rather than clobber specified output files
  --resume <filename>: Resume an aborted scan
  --noninteractive: Disable runtime interactions via keyboard
  --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
  --webxml: Reference stylesheet from Nmap.Org for more portable XML
  --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
MISC:
  -6: Enable IPv6 scanning
  -A: Enable OS detection, version detection, script scanning, and traceroute
  --datadir <dirname>: Specify custom Nmap data file location
  --send-eth/--send-ip: Send using raw ethernet frames or IP packets
  --privileged: Assume that the user is fully privileged
  --unprivileged: Assume the user lacks raw socket privileges
  -V: Print version number
  -h: Print this help summary page.
EXAMPLES:
  nmap -v -A scanme.nmap.org
  nmap -v -sn 192.168.0.0/16 10.0.0.0/8
  nmap -v -iR 10000 -Pn -p 80
SEE THE MAN PAGE (https://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES

可以看到列出了一長串的選項跟選項的說明，也可以從這裡看出 Nmap 的功能之強大，實際上 Nmap 的選項與功能還有更多詳情可以看 Nmap 官網的介紹文件 ( https://nmap.org/book/man.html )。

主機發現 Host Discovery

• 主機發現是什麼及其目的 ?
  主機發現是用來查看目標主機是否有開機並連上網。
  目的最直接來講就是你要測試的那台主機萬一沒上線，我們也做不了後續的任何事。

假設有個情境有一個人給了你一個網段要你對這個網段上所有的裝置做滲透測試，因為他沒有明確給你要測試的主機 IP，所以這個時候就需要對這個網段做掃描來查看有哪些裝置。

nmap -sn <IP範圍>

• -sn : 取消掃描 Port 的功能，也就是指掃描主機是否在線上。

實際示範 :

nmap -sn 192.168.31.0/24
Starting Nmap 7.95 ( https://nmap.org ) at 2026-09-22 11:35 EDT
Nmap scan report for 192.168.31.1
Host is up (0.0036s latency).
MAC Address: 00:50:56:C0:00:08 (VMware)
Nmap scan report for 192.168.31.2
Host is up (0.00017s latency).
MAC Address: 00:50:56:F3:35:E0 (VMware)
Nmap scan report for 192.168.31.254
Host is up (0.00011s latency).
MAC Address: 00:50:56:E0:C9:60 (VMware)
Nmap scan report for 192.168.31.129
Host is up.
Nmap done: 256 IP addresses (4 hosts up) scanned in 8.51 seconds

• -sn : 取消掃描 Port 的功能，也就是指掃描主機是否在線上。
• 192.168.31.0/24 : 掃描的範圍，最後一個區段為 0 ，遮罩為 24 bit，表示範圍在 192.168.31.1 ~ 192.168.31.255 。

補充 : 遮罩為 255.255.255.0 對 192.168.31.0 做 互斥或

可以看到掃描結果為 256 個 IP 只有 4 個有在線上。

表示範圍的方式 ( 也可以單獨只對一個位址做掃描 ) :

1. 空格格開

192.168.31.131 192.168.31.129 192.168.31.254

2. 遮罩

192.168.31.0/24

3. 位址為相鄰的情況

192.168.31.100-150 

除了這些方式外我們也可以把記有一連串 IP 的文字檔，塞進去給 Nmap 掃。

文字檔內容 :

cat scan.txt
192.168.31.1 
192.168.31.100-150 
example.com

掃描指令 :

nmap -iL ./scan.txt -sn

• iL : 指定輸入檔案來讀取掃描目標。
• -sn : 取消掃描 Port 的功能，也就是指掃描主機是否在線上。

總結

今天就只介紹主機發現的功能使用，雖然篇幅比較短，但這個指令也是非常重要的用法，基本上我每次打靶機都會先用這個指令或者是 ping 來確認我是不是可以成功碰得到目標，但 ping 只能對一個目標還是 -sn 好用一點，明天開始會介紹 Port Scan 的部分會順便帶一點 TCP/IP 和 Wireshark 的內容來解釋一下 TCP Port Scan 的原理，那就明天見啦。

延伸閱讀

• Nmap Reference Guide