linux nmap port scan

I use nmap constantly for connectivity checks — verifying firewall rules, confirming a service is actually listening on the expected port, or debugging why two services can’t talk to each other. The firewall and ping-blocking options are especially useful in enterprise environments where ICMP is often blocked.

• Port scan using nmap

Download and install nmap

• Scan all ports

$ nmap localhost

• Scan specific port

$ nmap -p 8080 localhost

• Scan specific port range

$ nmap -p 8080-9090 localhost

• Scan server which is blocking pings

$ nmap -sT -P0 -p 8080 localhost

$ # -sT (TCP connect)

• Scan server with firewall enabled ACK Scan

$ nmap nmap -sA -p 8080 localhost

$ #ACK Scan (-sA)