Networking Interactive Hub
Nine tools covering every networking topic on the GCSE and A-Level specification.
TCP/IP Stack
Click a layer to read what it does and what its protocols are. Then use the Protocol Drill below to test yourself.
Encapsulation
Travelling down the sender's stack, each layer adds its own header. Travelling up the receiver's stack, each layer strips its header back off.
Application Layer
PDU name: Message
Key protocols:
- HTTP (port 80) - web browsing
- HTTPS (port 443) - encrypted web browsing
- FTP (port 20/21) - file transfer
- SMTP (port 25) - sending email
- POP3 (port 110) - retrieving email (downloads and deletes from server)
- IMAP (port 143) - email access (keeps mail on server)
- DNS (port 53) - resolves domain names to IP addresses
- SSH (port 22) - secure remote access
Protocol Drill
Which layer does this protocol belong to?
Network Topology Builder
Select a component from the palette then click the canvas to place it. Switch to Connect mode and click two components to wire them. Drag to reposition. Right-click to delete.
Components
Guided Challenges
Use the canvas above to complete each challenge, then press Check.
Build a star topology: place 1 switch and at least 4 computers, all connected to the switch. This is the most common topology in modern LANs.
Build a bus topology: place 1 hub and at least 3 computers, all connected to the hub. Every device shares a single communication line.
Build two separate LANs (each with a switch and 2+ computers) and connect them via a router. This simulates a basic WAN / internet gateway setup.
Press Load then look at the diagram and identify what topology has been loaded. Choose below.
Subnet Calculator
Enter an IP address and subnet mask. The calculator shows the binary AND operation used to derive the network address, broadcast address, and usable host range - exactly as required in exams.
Test Yourself
Calculate the network address, broadcast address, and number of usable hosts for the IP and mask below.
Packet Switching Simulator
The message CodeBash: Number 1 programming platform! is split into 4 numbered packets. Each travels via a different route through 6 routers. Packet 3 ("programming") is dropped mid-route and must be retransmitted - watch the gap appear in the message then fill in when the retransmit arrives.
Use Step to advance one hop at a time. Use Play to run continuously.
1. Message Breakdown - Splitting into Packets
14 bytes
20 bytes
20 bytes
"CodeBash:" etc.
4 bytes
2. Routing Across the Network - 6 Routers
3. Destination - Reassembly Buffer
Packets arrive out of sequence order. They are held in the buffer below until all arrive, then sorted by sequence number to reconstruct the original message.
DNS Resolution
Domain Name System (DNS) translates human-readable domain names (e.g. www.codebash.co.uk) into IP addresses that routers can use. Press Next Step to walk through each stage using exact exam terminology.
Exam Glossary - Key DNS Terms
HTTP Request / Response Cycle
The sequence below shows every message exchanged when you type a URL into your browser and press Enter. Press Next Step to walk through it. This is a common 6-mark exam question.
Protocol Reference
All major networking protocols with their TCP/IP layer, port number, transport type, and purpose. Filter by layer to focus on what you need.
| Protocol | Layer | Port | Transport | Purpose |
|---|
IP Addressing
Explore IPv4 binary conversion, MAC addresses, and IPv6. Use the drill to practise converting between decimal and binary - a common exam calculation.
Binary to Decimal
Toggle bits to build an IP address. Each bit's column weight is shown above.
Decimal to Binary
Enter a dotted decimal IP and see the full binary representation.
What is an IPv4 Address?
An IPv4 address is a 32-bit number written as four decimal octets separated by dots (e.g. 192.168.1.100). Each octet represents 8 bits and ranges from 0 to 255. IPv4 supports approximately 4.3 billion unique addresses.
The subnet mask determines which part of the address identifies the network and which part identifies the host within that network. Routers use the network address (IP AND subnet mask) to forward packets.
IPv4 is divided into classes (A /8, B /16, C /24) and private address ranges (10.x.x.x, 172.16-31.x.x, 192.168.x.x) that are not routed on the public internet.
MAC Address
A MAC (Media Access Control) address is a 48-bit hardware address permanently assigned to a network interface card (NIC) by the manufacturer. It is written as 6 pairs of hexadecimal digits separated by colons, e.g. A4:C3:F0:85:AC:2D.
MAC addresses operate at the Network Access layer and are used for delivery within a local network (LAN). Unlike IP addresses, they do not change when a device moves between networks.
The first 3 bytes (24 bits) identify the manufacturer (OUI - Organisationally Unique Identifier). The last 3 bytes identify the specific device.
MAC Address Explorer
Click any hex byte to change it. The binary breakdown is shown below.
Last 3 bytes: 85:AC:2D - identifies the specific device
IPv6
IPv4's 32-bit address space (approximately 4.3 billion addresses) is exhausted. IPv6 uses 128-bit addresses, providing approximately 3.4 x 1038 unique addresses - enough for every grain of sand on Earth to have trillions of addresses.
An IPv6 address is written as 8 groups of 4 hexadecimal digits separated by colons:
Leading zeros within each group may be omitted, and one consecutive sequence of all-zero groups may be replaced with :::
IPv6 Address Breakdown
Written as: 32 hexadecimal characters (each hex digit = 4 bits)
Unique addresses: 2128 = approx. 3.4 x 1038
IPv4 vs IPv6 Comparison
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Format | Dotted decimal | Colon-separated hex |
| Address space | ~4.3 billion | ~3.4 x 1038 |
| NAT needed? | Yes (address exhaustion) | No |
| Header | Variable length, more complex | Fixed 40-byte header |
| Status | Still dominant | Growing adoption |
Binary Conversion Drill
Convert the IP address to its binary representation. Write each octet as 8 bits, separated by dots.
Client-Server vs Peer-to-Peer
Two fundamentally different network models. In client-server, all clients communicate through a dedicated central server. In peer-to-peer (P2P), each device acts as both client and server, communicating directly with others. Press Animate to see a request flow through each model.
Client-Server
- Centralised control and security
- Easy to back up and manage data centrally
- User accounts managed centrally
- Consistent performance for clients
- Server is a single point of failure
- Expensive to set up and maintain
- Server becomes a bottleneck under load
Peer-to-Peer (P2P)
- No single point of failure
- Cheap and easy to set up
- Each peer can share resources directly
- Scales well as more peers join
- No centralised security or backup
- Difficult to manage or audit devices
- Performance varies between peers