SYN scan is the default and most popular scan option for good reason. It can be performed quickly, scanning thousands of ports per second on a fast network not hampered by intrusive firewalls. SYN scan is relatively unobtrusive and stealthy, since it never completes TCP connections. It also works against any compliant TCP stack rather than depending on idiosyncrasies of specific platforms as Nmap's FIN/NULL/Xmas, Maimon and idle scans do. It also allows clear, reliable differentiation between op...
Probe Response, Assigned State ; Any UDP response from target port (unusual), open ; No response received (even after retransmissions), open filtered ; ICMP port unreachable error (type 3, code 3), closed
One way to determine whether a TCP port is open is to send a SYN (session establishment) packet to the port. The target machine will respond with a SYN/ACK (session request acknowledgment) packet if the port is open, and RST (reset) if the port is closed. This is the basis of the previously discussed SYN scan. A machine that receives an unsolicited SYN/ACK packet will respond with a RST. An unsolicited RST will be ignored. Every IP packet on the Internet has a fragment identification number (IP ...
Name, Description ; name, Contains the service name Nmap decided on for the port. ; name_confidence, Evaluates how confident Nmap is about the accuracy of name , from 1 (least confident) to 10. If port.version.service_dtype is "table" , this is 3. ; product , version , extrainfo , hostname , ostype , devicetype, These five variables are the same as those described under <versioninfo> in the section called “ match Directive” .
Probe Response, Assigned State ; TCP RST response, unfiltered ; No response received (even after retransmissions), filtered ; ICMP unreachable error (type 3, code 1, 2, 3, 9, 10, or 13), filtered
Experts understand the dozens of scan techniques and choose the appropriate one (or combination) for a given task. Inexperienced users and script kiddies, on the other hand, ...
Converts <target> from a hostname into an IPv4 address using DNS. If an IP address is specified instead of a hostname this lookup is skipped. Pings the host, by default with an ICMP echo request packet and a TCP ACK packet to port 80, to determine whether it is up and running. If not, Nmap reports that fact and exits. I could have specified -Pn to skip this test. See Chapter 3, Host Discovery (“Ping Scanning”). Converts the target IP address back to the name using a reverse-DNS query. Because of the way DNS works, the reverse name may not b ...
scan (nmap -F [target]) – Performing a basic port scan for fast result. Host discovery – Identifying hosts on a network. For example, listing the hosts that respond to TCP and/or ICMP...
List scan is a degenerate form of host discovery that simply lists each host on the network(s) specified, without sending any packets to the target hosts. By default, Nmap still performs reverse-DNS resolution on the hosts to learn their names. Nmap also reports the total number of IP addresses at the end. List scan is a good sanity check to ensure that you have proper IP addresses for your targets. If the hosts display domain names you do not recognize, it is worth investigating further to prevent scanning the wrong company's network. ...
Hosts found, Probe ; 62.47%, -PE ; 44.17%, -PS443 ; 43.28%, -PA80