TCP Transport Layer Quiz

Application Layer

• Supports end-user applications
• Works with session and presentation layers for network services
• Protocols interact with end user applications
• Well-known TCP/IP application layer protocols operate
• Web and email protocols operate
• DNS and DHCP operate
• File transfer protocols operate

Application, Presentation, and Session

• Application Layer
  • Closest to the end user
  • Used to exchange data between programs running on source and destination hosts
• Presentation Layer
  • Formats data
  • Compresses data
  • Encrypts data
• Session Layer
  • Creates and maintains dialogs between source and destination applications

TCP/IP Application Layer Protocols

• Domain Name Server (DNS) – TCP, UDP 53 - translates domain names like cisco.com to IP addresses
• Bootstrap Protocol (BOOTP) - superseded by DHCP
• Dynamic Host Configuration Protocol (DHCP) UDP client 68, server 67 - dynamically assigns IP addresses to client stations during startup
• Simple Mail Transfer Protocol (SMTP) TCP 25 - enables clients to send email to a mail server
• Post Office Protocol (POP) TCP 110 - enables clients to retrieve email from a mail server
• Internet Message Access Protocol (IMAP) TCP 143 - enables clients to retrieve and maintain email on the server
• File Transfer Protocol (FTP) -TCP 20 and 21 - reliable, connection-oriented, and acknowledged file delivery protocol
• Trivial File Transfer Protocol (TFTP) UDP 69 - simple connectionless file transfer protocol
• Hypertext Transfer Protocol (HTTP) TCP 80, 8080 - set of rules for exchanging text, graphic images, etc. on the World Wide Web
• Hypertext Transfer Protocol Secure (HTTPS) TCP, UDP 443 - uses encryption and authentication to secure communication

Web and Email Protocols

• Hypertext Transfer Protocol (HTTP)
  • Request/response protocol
  • Three common HTTP message types: GET, POST, PUT
• HTTP Secure (HTTPS)
  • Uses encryption and authentication to secure data
• Email Protocols
  • Email clients communicate with mail servers to send and receive email
  • Mail servers communicate to transport messages from one domain to another
    • Simple Mail Transfer Protocol (SMTP) - send email
    • Post Office Protocol (POP) - retrieve email
    • Internet Message Access Protocol (IMAP) - retrieve email

IP Addressing Services

• Domain Name Service (DNS)

  • Converts numeric addresses into simple names
  • Automated service that matches resource names with numeric network addresses

• DNS Message Format

  • Uses the same message format for all types of client queries and server responses
  • Handles error messages
  • Transfers resource record information between servers

• DNS Hierarchy

  • Hierarchical structure of DNS servers that contain resource records

• nslookup command

  • Utility to query name servers to resolve a given host
  • Troubleshoots name resolution issues
  • Verifies name server status

• DHCP

  • Dynamic Host Configuration Protocol
  • Automates the assignment of IPv4 addresses
  • Leases addresses for a time, then returns to pool

• DHCP Operations -Uses commands such as DHCPDISCOVER, DHCPOFFER, DHCPREQUEST and DHCPACK

• File Transfer Protocol (FTP) -Requires two connections between the client and the server

File Sharing Services

• Server Message Block (SMB)
  • Client/server file sharing protocol
  • Primarily used for file-sharing and print services (Microsoft networking)

The Transport Layer

• Transport Layer Characteristics

  • Supports network communication

• Transport Layer Session Establishment

  • Establishes communication sessions

• Transport Layer Reliability

  • Establishes reliable communications

• Role of the Transport Layer

  • Responsible for logical communication between applications
  • Acts as a link between the application layer and lower layers

• Transport Layer Responsibilities -Tracks conversations between applications -Manages multiple conversations

  • Divides large data blocks into manageable pieces

• Transport Layer Responsibilities (Continued) -Segments/reassembles data -Adds header information -Identifies applications using port numbers

• Conversation Multiplexing -Simultaneously handles multiple data streams

• Transport Layer Protocols

  • TCP and UDP
    • TCP is connection-oriented and reliable
    • UDP is connectionless and fast

• Transmission Control Protocol (TCP)

  • Reliable, full-featured transport layer protocol
  • Ensures all data arrives at the destination
  • Uses fields to guarantee delivery
  • Analogous to sending tracked packages
  • Manages reliability and flow control using operations like:
    • Numbering and tracking data segments
    • Acknowledging received data
    • Retransmitting unacknowledged data
    • Sequencing data that might arrive out of order
    • Sending data at an efficient rate

• TCP Header

  • Stateful protocol keeping track of communication session
  • Adds 20 bytes (160 bits) of overhead when encapsulating application data

• TCP Header Fields

  • Identifies source and destination applications by port number
  • Details regarding data reassembly
  • Header length

• User Datagram Protocol (UDP)

  • Simpler transport layer protocol than TCP
  • Fewer header fields than TCP
  • No reliability or flow control
  • Faster processing than TCP
  • Connectionless and stateless protocol

• UDP Header

  • No tracking of communication sessions
  • Only 8 bytes of overhead

• Socket Pairs

  • Combining source and destination ports and IP addresses
  • Used to distinguish between multiple processes on a client or server

• TCP Server Processes -Each application on a server is assigned a port number -One port per application

• TCP Connection Establishment Steps -Step 1: SYN (initial client request) -Step 2: ACK and SYN (server acknowledges and requests a server-to-client communication session) -Step 3: ACK (client validates server-to-client communication)

  • Connection is now fully established.

• Session Termination -FIN to close connection -Two-way handshake (FIN, ACK segments)

• TCP Reliability -Guaranteed and ordered delivery of data -Mechanisms for data loss & retransmission, handling out-of-order data

• TCP Flow Control -Regulates data flow for reliability -Window size determines number of bytes sent before acknowledgment

• Maximum Segment Size (MSS) -Maximum amount of data in a TCP segment

• Congestion Avoidance -Protocol to avoid loss when network conditions degrade

Network Layer

• Network Layer Protocols

  • Explains how network layer protocols and services support communications
  • Describes the purpose of the Network Layer in data communication
  • Explains why the IPv4 protocol requires other layers for reliability
  • Explains the role of the major header fields in IPv4 packets

• Routing

  • Explains how routers enable end-to-end connectivity
  • Explains how network devices use routing tables to direct packets

• Router Configurations -Configuring a router with basic settings -Configuring initial settings on a Cisco IOS router -Configuring two active interfaces on a Cisco IOS router -Configuring devices to use the default gateway

• Network Layer in Communications

  • Network layer resides at Layer 3 of OSI model
  • Provides services to allow end-devices to exchange data across a network -Uses four processes to provide end-to-end transport

• Network Layer Protocols

  • Internet Protocol Version 4 (IPv4)
  • Internet Protocol Version 6 (IPv6)

• IPv4 Packet Header

  • Contains binary fields for various settings
  • Version, Header Length, DS (Differentiate Services)/DiffServ, TTL, Protocol

• IPv6 Packet

  • Simpler header than IPv4
  • Advantages over IPv4:
    • Larger address space
    • Improved packet handling
    • Eliminates NAT for IP address sharing