Rebecca has noted multiple entries in her logs about users attempting to connect on ports that are either not opened or ports that are not for public usage. How can she restrict this type of abuse by limiting access to only specific IP addresses that are trusted by using one of the built-in Linux Operating System tools?

A.
Ensure all files have at least a 755 or more restrictive permissions.

B.
Configure rules using ipchains.

C.
Configure and enable portsentry on his server.

D.
Install an intrusion detection system on her computer such as Snort.

Explanation:
ipchains is a free software based firewall for Linux. It is a rewrite of Linux’s previous IPv4 firewalling code, ipfwadm. In Linux 2.2, ipchains is required to administer the IP packet filters. ipchains was written because the older IPv4 firewall code used in Linux 2.0 did not work with IP fragments and didn’t allow for specification of protocols other than TCP, UDP, and ICMP.