Networking Fundamentals

• Data is moved across networks similarly to items moved between addresses using a moving truck
• Data is put inside a "moving truck," moved across a network, and then "unloaded" at the destination

Network Topology

• The network topology is like the road upon which the moving truck travels
• This could be an ethernet, DSL, or cable modem network
• Inside the "truck" (IP), a box of data (TCP or UDP) contains the actual application data

Analogy Breakdown

• Road: Network topology (ethernet, DSL, etc.)
• Truck: Internet Protocol (IP), responsible for moving data
• Box: TCP or UDP data
• Contents of Box: Application data (web browsing, file transfer, etc.)

Protocol Encapsulation

• Ethernet encapsulates IP traffic
• IP encapsulates TCP or UDP data
• TCP/UDP encapsulates application data (e.g., HTTP)
• Web browsing traffic is packaged within TCP, then IP, then Ethernet for network transit

TCP and UDP Protocols

• TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are two different ways to move data across a network
• Operate at Layer 4 of the OSI model
• Allow multiple applications to use the network simultaneously via multiplexing

TCP Details

• Connection-oriented protocol, establishes a formal connection before data transfer
• Connection is formally terminated after communication
• Adds overhead due to connection setup and teardown
• A reliable mode of communication
• Requires acknowledgments for sent data, like a return receipt
• Numbers data for reassembly if lost or out of order
• Allows receiving device to control traffic flow

UDP Details

• Connectionless protocol, sends data without a formal setup process
• Unreliable form of delivery, no guarantee of receipt
• No acknowledgments or return receipts
• No built-in mechanism to recover lost data or reorder data
• Sending device determines the data transmission rate without feedback from the receiver

TCP vs UDP Use Cases

• Applications requiring guaranteed delivery often use TCP
• Applications less concerned about guaranteed delivery may use UDP

IP Addresses and Ports

• IP truck is going to deliver data from one IP address to another
• Analogous to physical addresses for houses, computers have IP addresses
• IP delivers data to the destination IP address
• Data is directed to specific applications via port numbers

Port Numbers

• Port numbers are written on the outside, specifying its destination within the host
• Port 80 is commonly associated with unencrypted web traffic (HTTP)
• Port 443 is commonly associated with encrypted web traffic (HTTPS)
• Port 25 is commonly associated with mail communication
• Port 123 is commonly associated with a time synchronization service

Required Information for Data Transfer

• Server IP address
• TCP or UDP protocol
• Server application port number
• Client IP address
• TCP or UDP protocol
• Client-side port number for responses

Port Number Groups

• Non-ephemeral ports are permanent port numbers used by server applications or services
• Range from 0 through 1,023
• Ephemeral ports are temporary port numbers, randomly chosen by the client for communication with the server
• TCP and UDP port numbers can range from 0 to 65,535

Port Security

• Changing a port number does not add any special kind of security

Well-Known Port Numbers

• Used to describe certain applications
• HTTP commonly uses TCP port 80
• HTTPS commonly uses TCP port 443

TCP vs UDP Port Conflicts

• TCP and UDP port numbers are different
• One application could uses TCP port 80 for communication and a different program can you UDP port 80 with no conflict

Server Port Usage Example

• A server with IP address 10.0.0.2 runs three services
• A web server using TCP port 80
• A voice over IP server using UDP port 5,004
• An email server using TCP port 143

Client-Server Communication

• Client (e.g., 10.0.0.1) communicates with server (e.g., 10.0.0.2) using appropriate port numbers for each service
• To send HTTP data, the client transmits TCP data over port 80
• To communicate voice over IP data, the client transmits UDP data over port 5,004
• To send email data, the client transmits TCP data over port 143
• The server uses port numbers to identify which application should receive the data

IP Packet Details

• By looking into an IP packet, the source and destination IP addresses, source and destination ports, and application data can be found
• Source IP: Client's IP address (e.g., 10.0.0.1)
• Destination IP: Server's IP address (e.g., 10.0.0.2)
• Source Port: Randomly chosen by the client (e.g., 3,000)
• Destination Port: Well-known port number for the service (e.g., 80 for HTTP)
• Data sent to the server will have the source and destination IP addresses, and source and destination port numbers simply switched so it can be returned

ICMP

• Internet Control Message Protocol
• Used for checking in on devices (like text messaging)
• Not commonly used for data transfer
• Commonly used for administrative purposes

ICMP Functions

• Check if a machine is operating by sending an ICMP request and expecting an ICMP response
• Notify devices when issues occur
• A router may send an ICMP message back to the workstation if it cannot communicate with an external network

Explore fundamental networking concepts using a moving analogy. Understand network topology, IP, TCP/UDP, encapsulation, and the OSI model. Learn about TCP's role in reliable communication and data transfer.