Audit the Packet's Journey

About this interactive

This audit follows one request through everything in Networking Basics. On the server, the song-list program runs as a network service, and a port number tells the server which service each request is for. The app and the service speak the same protocol. The laptop gets its IP address from DHCP when it joins a network; its MAC address is burned into its network card. It puts the request in an IP packet addressed to the server's IP address. The server is on another network, so the packet goes into an Ethernet frame addressed to the laptop's default gateway, the home router. The network card turns the bits into a signal on the medium, and the frame check sequence at the end lets the receiver spot damage. The home router is the edge of the LAN. The line to the ISP is the last mile; beyond the ISP is the backbone, run by many providers. Every router strips the frame, reads the packet's destination IP, and builds a new frame for the next hop. The destination IP stays the server's the whole way. On the server's LAN, the last router addresses a frame to the server's MAC. On a hub every machine receives it and only the server keeps it; if two machines send at once they collide, and each backs off for a random time before trying again. The server strips the headers and hands the request to the service by its port.

What you'll learn

Find the mistakes in a step-by-step account of one request crossing the network, from the app on a laptop to the service on the server
Correct each mistake with the rule it breaks: ports pick the service, MAC addresses are burned in, frames go to the next hop, routers read the destination IP, the last mile is not the backbone, broadcasts reach everyone, and colliding devices back off

Aligned to

ISC2 CC

4.1 Understand network security

CompTIA Network+

1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.

1.6 Compare and contrast network topologies, architectures, and types.

Cisco CCST Networking

1.1 Identify the fundamental conceptual building blocks of networks

Cisco CCNA

3.2 Determine how a router makes a forwarding decision by default

CompTIA A+ Core 1

2.4 Summarize services provided by networked hosts.

Key terms

Network Service: A program running as a background service on a machine that provides functionality to other devices on a network, operating independently of user login sessions.
Port: A logical endpoint for communication in a network, identified by a number that specifies a particular service or application.
MAC Address: A 48-bit hardware address assigned to a network interface and written as six hexadecimal octets, such as 00:1A:2B:3C:4D:5E. It identifies a device uniquely on a local network segment, and switches forward frames by looking it up in their MAC address table.
IP Address: A numerical label assigned to each device connected to a network that uses the Internet Protocol.
Packet: A unit of data formatted for transmission over a network, containing a header, payload, and sometimes a trailer.
Frame: The unit of data used at Layer 2 (Data Link layer) of the OSI model, containing source and destination MAC addresses, a payload (the encapsulated Layer 3 packet), and a frame check sequence for error detection. Frames are how switches and other Layer 2 devices think about and forward data.
Router: A network device that forwards data packets between networks based on IP addresses.
Broadcast: A transmission type in which one device sends a single packet that is delivered to every other device on the local network segment simultaneously. Broadcast traffic is contained within a broadcast domain and does not cross router boundaries.
Last Mile: The final leg of a telecommunications network that connects an ISP to the end user's location, often the most costly segment to deploy.
Carrier Sense Multiple Access with Collision Detection: The media access control method used in traditional Ethernet where devices listen before transmitting and detect collisions if two devices transmit simultaneously, then retransmit after a random backoff period. CSMA/CD is defined for half-duplex Ethernet and is not used in full-duplex switched networks.
Frame Check Sequence: A cyclic redundancy check value appended to the end of a data link frame that allows the receiver to detect transmission errors. The sending device calculates the FCS from the frame contents, and the receiving device recalculates it; a mismatch means the frame was corrupted and should be discarded.
Default Gateway: The router that a device uses to send traffic to destinations outside its local network.

Topics

Packet Frame Mac Address Ip Address Router Port Interactive Spot The Error

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