Free 702-100 Questions Attempt

The command netcat is a versatile networking utility that can be used to read from and write to network connections using TCP or UDP protocols. It is often used for debugging and investigating the network and can be used to connect to a remote TCP service.

References:

• BSD Specialist Exam 702 Objectives - Linux Professional Institute
• FreeBSD Handbook - Networking

A /24 IPv4 prefix provides 256 IP addresses, which is the number of addresses in one octet (2^8). A /28 subnet has 16 IP addresses (2^4). To calculate how many /28 subnets can fit into a /24 prefix, divide the total number of addresses in the /24 prefix by the number of addresses in a /28 subnet: 256 / 16 = 16. However, since each subnet has network and broadcast addresses that cannot be used for hosts, the actual number of usable subnets is less. In practice, you can create 16 subnets, each with 14 usable IP addresses for hosts.

References:

• Subnet Cheat Sheet
• IP Subnet Calculator

The /etc/nsswitch.conf file defines the order of the name resolution methods used on a NetBSD system. It specifies the sources and their priority for various databases, such as hosts, services, protocols, etc. The sources can be files, DNS, NIS, or other services. For example, the following line in /etc/nsswitch.conf indicates that the hosts database should be looked up first in the /etc/hosts file, then in the DNS server, and finally in the NIS server:

hosts: files dns nis

References:

• nsswitch.conf(5) - NetBSD Manual Pages
• Chapter 23. The NetBSD Network Configuration Files

The excerpt C is a valid if condition in the Bourne shell because it uses the correct syntax and operators for the test command. The syntax of the if statement in the Bourne shell is:

if test-commands; then consequent-commands; [elif more-test-commands; then more-consequents;] [else alternate-consequents;] fi

The test-commands are any commands that return a status of 0 (true) or non-zero (false). The test command is a common way to perform various tests on files, strings, and numbers. The test command has the following format:

test expression

The expression consists of one or more primaries, which are unary or binary operators that evaluate to true or false. The primaries can be combined with the following operators:

! expression: Logical NOT expression -a expression: Logical AND expression -o expression: Logical OR ( expression ): Parentheses for grouping

The excerpt C uses the test command with the following expression:

“$var” = “test”

This expression tests if the value of the variable $var is equal to the string “test”. The = operator is a string comparison operator that returns true if the strings are equal. The double quotes around the variable and the string are used to prevent word splitting and globbing by the shell. The spaces around the operator are also required by the test command.

The excerpt C also uses the correct syntax for the then and fi keywords, which mark the beginning and the end of the if statement. The then keyword must be on the same line as the test command, or on a new line after a semicolon. The fi keyword must be on a new line.

The other excerpts are invalid for various reasons:

• The excerpt A uses the && operator instead of the -a operator for logical AND. The && operator is a shell operator that executes the second command only if the first command succeeds. The test command does not recognize the && operator as a valid argument. The excerpt A also uses the != operator instead of the -ne operator for numeric comparison. The != operator is a string comparison operator that returns true if the strings are not equal. The -ne operator is a numeric comparison operator that returns true if the numbers are not equal.
• The excerpt B uses the [ [ construct instead of the test command. The [ [ construct is a shell keyword that performs conditional expressions similar to the test command, but with some extensions and differences. The [ [ construct is not part of the POSIX standard and is not supported by all shells. The Bourne shell does not support the [ [ construct, and will treat it as a command name. The excerpt B also uses the wrong syntax for the then keyword, which must be on a new line or after a semicolon.
• The excerpt D uses the wrong syntax for the test command, which requires a space after the opening bracket and before the closing bracket. The excerpt D also uses the wrong syntax for the fi keyword, which must be on a new line.