Installation guide

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for SYN-ACK reply, and then determines port state based on a reply – or lack of.
SNMP Scan
Direct Nessus to scan targets for a SNMP service. Nessus will guess relevant SNMP
settings during a scan. If the settings are provided by the user under “Preferences”,
this will allow Nessus to better test the remote host and produce more detailed audit
results. For example, there are many Cisco router checks that determine the
vulnerabilities present by examining the version of the returned SNMP string. This
information is necessary for these audits.
Netstat SSH Scan
This option uses netstat to check for open ports on the target host. It relies on the
netstat command being available via a SSH connection to the target. This scan is
intended for Unix-based systems and requires authentication credentials.
Netstat WMI Scan
This option uses netstat to check for open ports from the local machine. It relies on
the netstat command being available via a WMI connection to the target. This scan
is intended for Windows-based systems and requires authentication credentials.
Ping Host
This option enables the pinging of remote hosts to determine if they are alive.
This option is not recommended when scanning between virtual hosts on
the same system.
The “Port Scan Options” frame directs the scanner to target a specific range of ports. The following values are allowed
for the “Port Scan Range” option:
Table 21 – Values for Port Scan Options
Value
Description
“default”
Using the keyword “default”, Nessus will scan approximately 4,789 common ports
(found in the nessus-services file).
Custom List
A custom range of ports can be selected by using a comma delimited list of ports or
port ranges. For example, “21,23,25,80,110” or “1-1024,8080,9000-9200” are allowed.
Specifying “1-65535” will scan all ports.
The range specified for a port scan will be applied to both IPv4 and IPv6 addresses, as well as TCP and UDP
scans.
The “Performance” frame provides two options that control how many scans will be launched. These options are perhaps
the most important when configuring a scan as they have the biggest impact on scan times and network activity.
Table 22 – Performance Options
Option
Description
Max Checks Per Host
This setting limits the maximum number of checks a Nessus scanner will perform
against a single host at one time.
Max Hosts Per Scan
This setting limits the maximum number of hosts that a single Nessus scanner will
scan at the same time. If the scan is using a zone with multiple scanners, each
scanner will accept up to the amount specified in the Max Hosts Per Scan option. For