A Comprehensive Scanning for Open, Closed and Filtered Ports in the Computer Systems and Networks

Abstract

In this paper a comprehensive scanning for open, closed and filtered ports in the computer systems and networks is made.

Investigating the Network Traffic Using the Command-Line Packets Sniffer Tcpdump in Kali Linux

“…In this case localhost:34830 (192.168.80.130) sends SYN flag to host localhost:http (OJS platform). After that the localhost:http sends SYN-ACK flags to the host localhost:34830 [3,4,5,6,15,16,17]. Finally, localhost:34830 sends ACK flag to the host localhost:http in order to finish the establishment of three-way handshake between the hosts.…”

“…of the DNS records for the Bulgarian mail server "abv.bg". This information thanks to the website NsLookup.io is revealed [1,2,3,4,15,17,20]. The command "tcpdump portrange 1-79" filters the network connections from port 1 to 79.…”

“…In the modern computer practice, various types of network programs are used to analyze and monitor the network packets that are sent between the individual hosts in a local and global computer networks. Most of the network packet analysis and monitoring programs are made so that the system administrator enters commands with options and parameters in the command line (terminal) [1,4,5,7,9,10,13,18,19,20,21]. Another part of them with a graphical user interface are made.…”

“…The special feature of this scientific article is that the different network states of the bits (flags) in the header of the TCP protocol will be considered. The flags that are used in the TCP protocol header are the following [1,2,3,4,5,6,11,12,14,15,20,21]:…”

“…4 and 5 show the achieved results after execution the command "tcpdump net 192.168.80.0/24 and tcp port 80 -v". After executing this command, only network packets that use the protocol HTTP are displayed and filtered [3,4,12,13,15,16,19]. If the system administrator wants to receive only network information about the HTTPS protocol, then instead of port 80, it must be written port 443.…”