Packet Journey Animator — TechKnowSurge

About this interactive

What you’re seeing: one packet travelling from your laptop to a web server, through the five things that actually handle it — a switch, your router, your ISP’s network, and the server. Press Step to move one hop at a time or Play the journey to watch it run, at 1× or 2×. Why it matters: the single most common misunderstanding in beginner networking is that the addresses on a packet are fixed for the whole trip — that the frame leaving your laptop has the web server’s MAC address on it. It does not, and it cannot. How to use it: at each stop, read the callout above the device for what that device just did, then check the panel on the right, which shows the packet’s two MAC addresses, two IP addresses and TTL as they stand at that moment and highlights whatever just changed. Watch the counters beside them. By the end, the MAC pair has been rewritten on every single link it crossed, the source IP was rewritten exactly once — by NAT, at the edge of your network — and the destination IP was never rewritten at all.

How to use this tool

A packet is about to travel from your laptop to a web server on the internet, and the five boxes across the top are what it passes through: your client, a switch, your router, your ISP, and the server itself.

Press Step to move one hop at a time, or Play the journey to watch the whole trip run itself. The 1× and 2× buttons set how fast it plays, Back reverses one step, and Reset puts the packet back on the laptop.

At every stop, a callout above the device says what that device just did — a MAC address lookup at the switch, an IP routing decision at the router, a NAT translation at the edge of your network — and the sentence underneath explains it properly.

The panel on the right is the part worth watching. It shows the packet’s two MAC addresses, its two IP addresses and its TTL as they stand right now, highlights whichever ones the current step rewrote, and counts how many times each has been written. Two patterns come out of that count, and they are the whole point of the exercise: the MAC addresses are replaced on every single link, because a MAC address only means anything between two devices on the same wire — and the destination IP is never rewritten at all.

The source IP is rewritten, exactly once, when NAT swaps your private 192.168.1.50 for the router’s public address on the way out. Watch where that happens: at the edge of your network, and nowhere else on the trip.

What you'll learn

Trace a packet from a client to a server on the internet and name what each device on the path does to it: the MAC address lookup at the switch, the routing-table decision and TTL decrement at each router, and the NAT translation at the edge of the network
Explain why the source and destination MAC addresses are replaced on every link a packet crosses while the destination IP address stays the same end to end, and identify the one place on the trip where an IP address is rewritten

Aligned to

Cisco CCST Networking

4.5 Explain basic switching concepts

4.4 Explain basic routing concepts

2.1 Compare and contrast private addresses and public addresses

CompTIA Network+

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

CompTIA A+ Core 1

2.2 Compare and contrast common networking hardware.

2.6 Compare and contrast common network configuration concepts.

Cisco CCNA

1.13 Describe switching concepts

3.2 Determine how a router makes a forwarding decision by default

Key terms

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.
Encapsulation: The process of wrapping data with protocol headers as it passes down the layers of the OSI model.
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.
Switch: A network device that connects devices within a LAN and forwards traffic based on MAC addresses.
Router: A network device that forwards data packets between networks based on IP addresses.
Default Gateway: The router that a device uses to send traffic to destinations outside its local network.
Address Resolution Protocol: A protocol used to map an IP address to a physical MAC address on a local network.
Routing Table: A database stored in a router that lists known network destinations, the metric (cost) to reach them, and the next-hop address or outgoing interface to forward packets toward those destinations. Routers consult this table for every packet they forward.
Hop: A single step in the path a packet takes through the network, specifically the transit from one router to the next closest router toward the destination. The number of hops a packet must travel is used as a routing metric by distance-vector protocols like RIP.
Time to Live: A value in a packet that limits its lifespan on a network, preventing it from circulating indefinitely.
Network Address Translation: A method that maps private IP addresses to a public IP address, allowing multiple devices to share a single public IP.
Private IP Address: An IP address from a reserved range (Class A: 10.0.0.0–10.255.255.255, Class B: 172.16.0.0–172.31.255.255, Class C: 192.168.0.0–192.168.255.255) used within private networks and not routable on the public internet.
Public IP Address: A globally unique IP address assigned to a device or network that is routable and reachable across the public internet.
Internet Service Provider: A company that provides end users with access to the internet by connecting them to the internet backbone.

Topics

Networking Packet Routing Switching Mac Address Ip Address Default Gateway Arp Nat Ttl

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