Discovery Scan settings, port scanning limits, open ports, localhost port, NMAP Port Scan, and information security stack are some of the things that can be found in this post.

Discovery settings can't be configured in the scans if they are based on a policy.You can only change the settings in the policy.

The settings that are required by a particular policy are indicated in the interface.

If you choose the Custom preconfigured setting option, you can manually set Discovery settings in the following categories.

The following tables have settings for the Advanced Scan template.Default values and settings may be different depending on the template you choose.

The Host Discovery section has settings that are enabled.The remote host item is set to On when you first access the Host Discovery section.

The scans remote hosts on multiple ports to determine if they are still alive.General settings and ping methods are available.

The hosts that the Nessus scans do not respond to any ping methods.The option is only available for scans using the template.

The local host is included in the scans when enabled.When the host falls within the target network range, this is used.

If a host responds to ping, Nessus tries to avoid false positives by performing additional tests to make sure the response was not from a proxy or load balancer.If the host is firewalled, these checks can take a long time.

The address resolution protocol is used to ping a host.This only works on the local network.

The destination ports can be configured to use specific ports.The list of ports that are checked is given here.

The host is down if ICMP is not reachable from the gateway.An ICMP unreachable message may be returned when a ping is sent to a host that is down.When the scanner gets an ICMP Unreachable message, it considers the host dead.The approach helps speed discovery.

The same behavior is used for hosts that are up, but connected to a port or protocol that is not.The host is down when this option is enabled.

The User Datagram Protocol is used to ping a host.Communication is not done with handshake dialogues with the stateless protocol, UDP.Because of the nature of UDP services and screening devices, communication is not always reliable.

The scanner can perform a full Scan of Operational Technology devices that monitor environmental factors and the activity and state of machinery.

When the scanner is disabled, it uses smart scanning to identify OT devices and stop scanning after they're discovered.

The Wake-on-LAN menu controls which hosts to send WOL magic packets.

The hosts that you want to start with are provided by uploading a text file.

The settings in the Port scanning section define how the port scanner behaves.

If a port is not scanned with a selected port scanner, it is considered closed.

You can use a limited list of ports or port ranges to indicate a custom list.For example, 21,23,25,80,110 or 1-1024,8080,9000-9200.If you wanted to exclude port 0, you would type 1-65535.

The protocols you have selected in the Network Port Scanners group of settings are applied to the custom range specified for a port scans.

You can specify a split range for each protocol.If you want to use a different range of ports in the same policy, you would type T:1-1024,U:300-500.

You can specify a set of ports and individual ranges for each protocol.1-1023,T:1024-65535,U:1025.

Netstat is used to check for open ports from the local machine.It relies on the netstat command being available.This is for Linux-based systems.

If the appropriate credentials are provided by the user, the scanner can better test the remote host and produce more detailed audit results.It is possible to determine the vulnerabilities present by examining the version of the returned SNMP string.This information is needed for the audits.

Before relying on network port scans, the scanner relies on local port enumeration.

If a local port enumerator finds a port, the scanner will verify that the port is open.This approach helps determine if access control is being used.

To identify open TCP ports on the targets, use a full TCP three-way handshake.It is only possible if you are using Linux or FreeBSD.The SYN scanner is used on Windows and Mac OS X to avoid performance issues native to those operating systems.

The built-in Nessus SYN scanner can be used to identify open TCP ports.SYN scans do not initiate a full handshake.The port state is determined by the response or lack of response to a SYN packet sent to the port.

The Override Automatic Firewall Detection option can be set if you enable this option.

The ability to monitor how often resets are set is disabled by soft detection.

This description applies to the Override automatic firewall detection setting.

Due to the nature of the protocol, it is not possible to tell if a port is open or not.It is possible to increase the scanning time and produce unreliable results with the help of the UDP port scanner.If possible, use the netstat or SNMP port enumeration options.

The settings in the Service Discovery section attempt to map each open port with the service that is running on that port.

The scanning attempts to map each open port with the service that is running on that port.