Questions and Answers
Which port number is associated with the Secure HTTP protocol?
443
What is the primary function of the port numbered 25?
Sending Mails
Which protocol uses port 143 for accessing mails securely?
IMAPS
What is the purpose of port 22 in a Linux system?
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Where are standard service ports listed in a Linux system?
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Study Notes
Destination Port Identification
- A colon (:) is used to separate the IPv4 address from the destination port in a connection.
- Example: 200.216.10.15:443 for accessing the HTTPS service.
Transport Protocols
- TCP (Transmission Control Protocol)
- Connection-oriented transport protocol
- Establishes a connection between client and service
- Ensures packets are delivered properly, verifying integrity and order
- Re-transmits lost packets due to network errors
Transport Protocols (continued)
- UDP (User Datagram Protocol)
- Establishes a connection between client and service, but does not control data transmission
- Does not check for lost or out-of-order packets
- Application is responsible for implementing necessary controls
- Enables better performance in data flow for certain services
Port Usage
- Source and destination ports are used to access a service
- Ports are identified by a 16-bit field, allowing for 65,535 possible ports
- Services (destination) use ports 1 to 1023, called privileged ports with root access
- Origin of the connection uses ports 1024 to 65,535, called non-privileged or socket ports
- Port assignments are standardized and controlled by IANA (Internet Assigned Numbers Authority)
Standard Service Ports
- SSH: 22
- HTTP: 80
- FTP (data): 20
- FTP (control): 21
- Telnet: 23
- SMTP: 25
- DNS: 53
- POP3: 110
- NTP: 123
- Netbios: 139
- IMAP: 143
- SNMP: 161
- SNMPTRAP: 162
- LDAP: 389
- HTTPS: 443
- SMTPS: 465
- RSH: 514
- LDAPS: 636
- IMAPS: 993
- POP3S: 995
