Question

166 Chapter 8: TCP/IP Applications Getting Down to Business The way network communication all those ls and Os) goes in and out of a machine physically is through the NIC (network interface card). The way network communication goes in and out of a machine logically though, is through a program or service. A service is a program that runs in the background, independent of a logon, that provides functionalities to a system. Windows client machines, for instance, have a Workstation service that runs in the background and enables connections to remote network resources. It's not tied to a single user logon, and is always running in the background. As another example, when you turn on a Web server, you're starting a specific server service that isn't tied to a specific user logon. In the world of Linux, services are known as daemons. Well, then, how does network communication go in and out of a program or service? Let's say a single machine is running both an FTP (File Transfer Protocol) server, like FileZilla, and a Web (HTTP) server, like Apache. If both are accessible by the same IP address, how does the traffic for the FTP server get to the FTP server, and the traffic for the Web server get to the Web server? The way into and out of a program or service is through a port, which is an endpoint in communication, represented by a logical number. So, in addition to source and destination MAC addresses and source and destination IP addresses, there are source and destination ports. MAC addresses are found in frames at Layer 2 of the OSI model. IP addresses are found in packets at Layer 3. Port numbers are found in either TCP segments or UDP datagrams at Layer 4. Based on the destination port, the destination machine knows which program or service to send the data to. This is like a postal carrier bringing mail for tenants of an apartment building. The tenants all live at the same street address (like an FTP server and a Web server share the same IP address). However, the postal carrier knows to put the mail for Frank Thomas Peterson (FTP), who lives in Apartment 21, in the box for Apartment 21, and the mail for Helen Theresa Thomasina Parker (HTTP), who lives in Apartment 80, in the box for Apartment 80. Step 1 In your own words, explain the purpose of a logical port.

Answer 1

Step 1
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Port are logical address of any protocol another we can call it dedicated door for each protocol in which all the packets fall in that box or we can say mailbox for each protocol in which each protocol packets are dropped and then receiver will open that packet and read the content which sender has sent.

its nothing but a dedicated sepreate line for packet transmisison for each protocol.

Step 2
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21 for ftp prtocol
22 for ssh protocol
25 for smtp protocol
53 for dns protocol
67/68 is for udp
80 for http protocol
88 for tcp protocol
143 for Transmission Control Protocol.
389 for LDAP (Lightweight Directory Access Protocol)
443 for https
3389 for RDP remote desktop protocol

Step 3
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netstat -a : Displays all connections and listening ports.

netstat -b : Displays the executable involved in creating each connection or listening port.

netstat -n : Displays addresses and port numbers in numerical form.

netstat -o : Displays the owning process ID associated with each connection.

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