Comptia A+ 220-1201 Core
1_2026 Real Exam
Questions
2026-2027
Master Exam Prep Bundle
(Verified Questions & Answers)
A+ Grade Guaranteed
,2.1 TCP - Transmission Control Protocol Communication
2.1 TCP - Transmission Control Protocol • Connection-oriented
- A formal connection setup and close
• "Reliable" delivery
- Recovery from errors
- Manages out-of-order messages or retransmissions
• Flow control
- The receiver can manage how much data is sent
2.1 UDP - User Datagram Protocol Communication
2.1 UDP - User Datagram Protocol • Connectionless - No formal open/close to the connection
• "Unreliable" delivery
- No error recovery, no reordering of data or retransmissions
• No flow control
- Sender determines the amount of data transmitted
2.1 Why would you ever use UDP? • Real-time communication
- There's no way to stop and resend the data
- Time doesn't stop for your network
• Connectionless protocols
- DHCP (Dynamic Host Configuration Protocol)
- TFTP (Trivial File Transfer Protocol)
• The data might not get through
- The application keeps track and decides what to do
- It might not do anything
2.1 Communication using TCP • Connection-oriented protocols prefer a "return receipt"
- HTTPS (Hypertext Transfer Protocol Secure)
- SSH (Secure Shell)
• The application doesn't worry about
out of order frames or missing data
- TCP handles all of the communication overhead
- The application has one job
,2.1 Speedy delivery • The IP delivery truck delivers from one (IP) address to
another (IP) address
- Every house has an address, every computer
has an IP address
• Boxes arrive at the house / IP address
- Where do the boxes go? - Each box has a room name
• Port is written on the outside of the box
- Drop the box into the right room
2.1 Lots of ports • IPv4 sockets
- Server IP address, protocol, server application port #
- Client IP address, protocol, client port number
• Non-ephemeral ports - permanent port numbers
- Ports 0 through 1,023 - Usually on a server or service
• Ephemeral ports - temporary port numbers
- Ports 1,024 through 65,535
- Determined in real-time by the client
2.1 Port number (how many) • TCP and UDP ports can be any number between 0 and 65,535
• Most servers (services) use non-ephemeral
(not-temporary) port numbers
- This isn't always the case - it's just a number.
• Port numbers are for communication, not security
• Service port numbers need to be "well known"
• TCP port numbers aren't the same as UDP port numbers
2.1 Port numbers • Well-known port number
- Client and server need to match
• Important for firewall rules
- Port-based security
• A bit of rote memorization
- Becomes second nature after a while
• Make sure you know port number, protocol,
and how the protocol is used
2.1 FTP - File Transfer Protocol • tcp/20 (active mode data), tcp/21 (control)
- Transfers files between systems
• Authenticates with a username and password
- Some systems use a generic/anonymous login
• Full-featured functionality - List, add, delete, etc.
2.1 SSH - Secure Shell • Encrypted communication link - tcp/22
• Looks and acts the same as Telnet
, 2.1 Telnet • Telnet - Telecommunication Network - tcp/23
• Login to devices remotely
- Console access
• In-the-clear communication
- Not the best choice for production systems
2.1 SMTP - Simple Mail Transfer Protocol • SMTP - Simple Mail Transfer Protocol
- Server to server email transfer
- tcp/25
• Also used to send mail from a device to a mail server
- Commonly configured on mobile devices and
email clients
• Other protocols are used for clients to receive email
- IMAP, POP3
2.1 DNS - Domain Name System • Converts names to IP addresses - udp/53
- www.professormesser.com = 162.159.246.164
• These are very critical resources
- Usually multiple DNS servers are in production
2.1 DHCP - Dynamic Host Configuration Protocol • Automated configuration of IP address, subnet mask and
other options
- udp/67, udp/68
- Requires a DHCP server
- Server, appliance, integrated into a SOHO router, etc.
• Dynamic / pooled
- IP addresses are assigned in real-time from a pool
- Each system is given a lease and must renew at set
intervals
• DHCP reservation
- Addresses are assigned by MAC address in the DHCP
server
- Manage addresses from one location
2.1 HTTP and HTTPS • Hypertext Transfer Protocol
- Communication in the browser
- And by other applications
• In the clear or encrypted
- Supported by nearly all web servers and clients
1_2026 Real Exam
Questions
2026-2027
Master Exam Prep Bundle
(Verified Questions & Answers)
A+ Grade Guaranteed
,2.1 TCP - Transmission Control Protocol Communication
2.1 TCP - Transmission Control Protocol • Connection-oriented
- A formal connection setup and close
• "Reliable" delivery
- Recovery from errors
- Manages out-of-order messages or retransmissions
• Flow control
- The receiver can manage how much data is sent
2.1 UDP - User Datagram Protocol Communication
2.1 UDP - User Datagram Protocol • Connectionless - No formal open/close to the connection
• "Unreliable" delivery
- No error recovery, no reordering of data or retransmissions
• No flow control
- Sender determines the amount of data transmitted
2.1 Why would you ever use UDP? • Real-time communication
- There's no way to stop and resend the data
- Time doesn't stop for your network
• Connectionless protocols
- DHCP (Dynamic Host Configuration Protocol)
- TFTP (Trivial File Transfer Protocol)
• The data might not get through
- The application keeps track and decides what to do
- It might not do anything
2.1 Communication using TCP • Connection-oriented protocols prefer a "return receipt"
- HTTPS (Hypertext Transfer Protocol Secure)
- SSH (Secure Shell)
• The application doesn't worry about
out of order frames or missing data
- TCP handles all of the communication overhead
- The application has one job
,2.1 Speedy delivery • The IP delivery truck delivers from one (IP) address to
another (IP) address
- Every house has an address, every computer
has an IP address
• Boxes arrive at the house / IP address
- Where do the boxes go? - Each box has a room name
• Port is written on the outside of the box
- Drop the box into the right room
2.1 Lots of ports • IPv4 sockets
- Server IP address, protocol, server application port #
- Client IP address, protocol, client port number
• Non-ephemeral ports - permanent port numbers
- Ports 0 through 1,023 - Usually on a server or service
• Ephemeral ports - temporary port numbers
- Ports 1,024 through 65,535
- Determined in real-time by the client
2.1 Port number (how many) • TCP and UDP ports can be any number between 0 and 65,535
• Most servers (services) use non-ephemeral
(not-temporary) port numbers
- This isn't always the case - it's just a number.
• Port numbers are for communication, not security
• Service port numbers need to be "well known"
• TCP port numbers aren't the same as UDP port numbers
2.1 Port numbers • Well-known port number
- Client and server need to match
• Important for firewall rules
- Port-based security
• A bit of rote memorization
- Becomes second nature after a while
• Make sure you know port number, protocol,
and how the protocol is used
2.1 FTP - File Transfer Protocol • tcp/20 (active mode data), tcp/21 (control)
- Transfers files between systems
• Authenticates with a username and password
- Some systems use a generic/anonymous login
• Full-featured functionality - List, add, delete, etc.
2.1 SSH - Secure Shell • Encrypted communication link - tcp/22
• Looks and acts the same as Telnet
, 2.1 Telnet • Telnet - Telecommunication Network - tcp/23
• Login to devices remotely
- Console access
• In-the-clear communication
- Not the best choice for production systems
2.1 SMTP - Simple Mail Transfer Protocol • SMTP - Simple Mail Transfer Protocol
- Server to server email transfer
- tcp/25
• Also used to send mail from a device to a mail server
- Commonly configured on mobile devices and
email clients
• Other protocols are used for clients to receive email
- IMAP, POP3
2.1 DNS - Domain Name System • Converts names to IP addresses - udp/53
- www.professormesser.com = 162.159.246.164
• These are very critical resources
- Usually multiple DNS servers are in production
2.1 DHCP - Dynamic Host Configuration Protocol • Automated configuration of IP address, subnet mask and
other options
- udp/67, udp/68
- Requires a DHCP server
- Server, appliance, integrated into a SOHO router, etc.
• Dynamic / pooled
- IP addresses are assigned in real-time from a pool
- Each system is given a lease and must renew at set
intervals
• DHCP reservation
- Addresses are assigned by MAC address in the DHCP
server
- Manage addresses from one location
2.1 HTTP and HTTPS • Hypertext Transfer Protocol
- Communication in the browser
- And by other applications
• In the clear or encrypted
- Supported by nearly all web servers and clients
