FUNDAMENTALS OF COMPUTER

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COMPUTER THREATS SECURITY

WHAT IS A FIREWALL IN NETWORK SECURITY

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
iptables is used to configure, maintain and inspect IPv4 packet filtering rule tables in the Linux kernel. Several different tables can be defined. Each table contains a number of internal chains and can also contain user-defined chains. If the network technician wanted to deny access to port 443 of a certain Linux server, the command used in this case is represented in the alternative:
A
iptables-R INPUT-h tcp ____ dport 443-d REJECT
B
iptables-A INPUT-p tcp ____ dport 443-j DROP
C
iptables-L INPUT-d tcp ____ dport 443-j ACCEPT
D
iptables-I INPUT-s tcp ____ dport 443-d REJECT
Explanation: 

Detailed explanation-1: -iptables is a user-space utility program that allows a system administrator to configure the IP packet filter rules of the Linux kernel firewall, implemented as different Netfilter modules. The filters are organized in different tables, which contain chains of rules for how to treat network traffic packets.

Detailed explanation-2: -The iptables commands are as follows:-A-Appends the iptables rule to the end of the specified chain. This is the command used to add a rule when rule order in the chain does not matter.-C-Checks a particular rule before adding it to the user-specified chain.

Detailed explanation-3: -To clear the counters for all rules in a specific chain, use the-Z option and specify the chain. For example, to clear the INPUT chain counters run this command: sudo iptables-Z INPUT.

Detailed explanation-4: -The-D argument used with iptables deletes a specific rule. The-F option removes all rules in the chain. Use one of the methods to delete rules based on specifications, chains, or numbers, or to flush the entire chain.

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