Host Discovery

ARP Discovery

# arp-scan:
sudo arp-scan -I tap0 <IP>/24

# Nmap:
sudo nmap -n -sn <IP>/24 -PR -oG - | awk '/Up$/{print $2}'

ICMP Discovery

# fping: Ping sweep
fping  -a -g <IP>/24 2> /dev/nul

# fping: sweep, generate statistics and list alive hosts
fping -asgq <CIDR>/<IP>

# Nmap: Ping sweep and save to file
nmap -n -sn <IP>/24 -oG - | awk '/Up$/{print $2}' >> nmapresults.txt

Ping and ARP scan (combined)

fping  -a -g <IP> 2> /dev/null | sudo nmap -n -sn <IP> -PR -oG - | awk '/Up$/{print $2}' | uniq -u > AliveHosts.txt

TCP SYN Scan

For host discovery such as the command above we should also use non ICMP scanning techniques in the event ICMP is blocked on a host and we miss it. We can use the following command below to perform a TCP scan sweep.

nmap -n -sn -PS <IP>/24

TCP ACK Scan

nmap -n -sn -PA <IP>/24

UDP Ping Scan

Useful for bypassing firewalls that filter TCP traffic and allow UDP traffic. By default a UDP scan will scan ports 40 and 125.

nmap -sn -sU <IP>/24

Reverse DNS Lookup

nmap -R -sL <IP>/24

Additional Nmap Parameters

Parameter	Description
-n	Exclude name resolution
-R	reverse-DNS lookup
-sn	only perform host discovery (No port scan)
-sL	List targets that will be scanned

Host Discovery Techniques | Nmap Network Scanning