Port Numbers – The doors of Communication

Port numbers are important when it comes to Networking and Cyber Security. Networking, because no network is a network without ports, whether it’s your internet, your VOIP call or a remote session on another computer. So, it becomes very important to understand them and remember them when it comes to understand or hack the network. Yes, i said “hack”, don’t be surprised.

Let me tell you if you don’t know about it, checking out which ports are open in your network is the first step on trespassing it. But we’ll talk about that later, right now i’ll explain you what exactly are these.

Port numbers are nothing but the numbered doors in a system which allow nothing but packets. No, not any packet to any door, only the packet carrying the same number as the door is assigned with. Both TCP and UDP packets carry these port numbers to make sure the right packet reaches to it’s right job.  Ports are the endpoints of many type of communication and are always associated with IP address of source or the destination and Network Protocols.

Port numbers consist of 16-bit number that means there are currently 65535 port numbers. That’s a big number, isn’t it? Well, out of those, first 1024 are reserved to serve specific network services on the host. But for now, let’s focus on only a few which are very commonly used to run default assigned services. Here are these:

Important Port Numbers and their respective Protocols

15        —        Netstat

20        —        FTP data

21        —        FTP Command

23        —        Telnet

25        —        SMTP

42        —        WINS

53        —        DNS

67        —        Bootp

68        —        DHCP

80        —        HTTP

88        —        Kerberos

101      —        HOSTNAME

110      —        POP3

119      —        NNTP

123      —        NTP     (Network time protocol)

139      —        NetBIOS

161      —        SNMP

180      —        RIS

389      —        LDAP (Lightweight Directory Access Protocol)

443      —        HTTPS (HTTP over SSL/TLS)

520      —        RIP

79        —        FINGER

37        —        Time

3389    —        Terminal services

443      —        SSL (https) (http protocol over TLS/SSL)

220      —        IMAP3

3268    —        AD Global Catalog

3269    —        AD Global Catalog over SSL

500      —        Internet Key Exchange, IKE (IPSec) (UDP 500)

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