Network redundancy is the inclusion of extra components, especially multiple paths between any two connected devices, so that if one device or connection fails, data can still travel by a different route. It's the main way the Internet achieves fault tolerance (AP CSP Topic 4.2).
Network redundancy means building a network with more connections than it strictly needs. Per the CED, redundancy is "the inclusion of extra components that can be used to mitigate failure of a system if other components fail" (EK CSN-1.E.2), and the network version of that is having more than one path between any two connected devices (EK CSN-1.E.3).
Think of it like driving across a city. If there's only one road and it's closed, you're stuck. If the city is a grid, you just take a different street. The Internet works the same way. If a router or cable fails, routing protocols send subsequent data along a different route, if one exists (EK CSN-1.E.4). That's why a single broken server in another country doesn't take down your connection. The redundancy is already built into the design.
Network redundancy lives in Unit 4: Computer Systems and Networks, Topic 4.2 Fault Tolerance, under learning objective 4.2.A. That objective asks you to do three things: describe the benefits of fault tolerance, explain how a given system is fault-tolerant, and identify vulnerabilities to failure. Redundancy is your answer to the middle one. When a question asks how the Internet keeps working despite failures, the answer is almost always "redundant paths plus rerouting." It's also the flip side of vulnerability analysis. A device with only one connection to the network is a single point of failure, and spotting that is exactly what 4.2.A part c wants you to do.
Keep studying AP® Computer Science Principles Unit 4
Fault Tolerance (Unit 4)
Fault tolerance is the goal; redundancy is the mechanism. A system is fault-tolerant when it can support failures and still continue working, and the Internet achieves that mostly by having extra paths so no single failure is fatal (EK CSN-1.E.1, CSN-1.E.5).
Routing on the Internet (Unit 4)
Redundant paths are useless unless something actually picks a new path. Routing is the abstraction that does it. When a connection dies, routers automatically send subsequent packets along a different available route, so redundancy and routing work as a team.
Packets and the Internet's design (Unit 4)
Because data travels as independent packets, different packets from the same message can take different routes and still be reassembled at the destination. That packet-based design is what makes rerouting around failures practical instead of chaotic.
This is multiple-choice territory. Expect scenario questions where you pick the setup that best demonstrates redundancy, like a network administrator designing a fault-tolerant network for a financial institution, or a corporate network with backup connections between buildings. The right answer is the one with multiple independent paths or duplicate components, not just "a faster connection" or "a bigger server." You may also get the reverse task, identifying the vulnerability, where the answer is the device or link that everything depends on (a single point of failure). And watch for questions asking how redundancy improves reliability. The clean answer is that if one path or component fails, data is rerouted through another, so the system keeps operating.
These aren't synonyms. Fault tolerance is the property (the system keeps working when parts fail), and network redundancy is one way to get that property (extra paths between devices). On the exam, if a question asks how the Internet is fault-tolerant, redundancy is your evidence. If it asks what redundancy achieves, fault tolerance is your answer. They point at each other, but they're cause and effect, not the same thing.
Redundancy means including extra components that can take over when other components fail (EK CSN-1.E.2).
Network redundancy specifically means having more than one path between any two connected devices (EK CSN-1.E.3).
If a device or connection on the Internet fails, subsequent data is sent via a different route when one is available (EK CSN-1.E.4).
Redundancy is the mechanism, fault tolerance is the result; a system that keeps working through failures is fault-tolerant because of its redundancy.
A single point of failure, like a device with only one connection, is the classic vulnerability you should be able to spot under learning objective 4.2.A.
More redundancy generally means more reliability, but it also means more cost and complexity, which is why real networks balance the two.
It's having more than one path between any two connected devices on a network, so if one device or connection fails, data can be sent by a different route. It's covered in Topic 4.2 (Fault Tolerance) under learning objective 4.2.A.
No. Fault tolerance is the property of a system that keeps working when parts fail, and network redundancy is the most common way to achieve it. Redundancy is the how, fault tolerance is the what.
No. The CED is careful here: data is rerouted "if possible." If every path between two devices is broken, or a device has only one connection, communication still fails. Redundancy reduces the chance of failure; it doesn't eliminate it.
Extra paths mean no single failure can cut off communication. When a router or cable goes down, routing sends subsequent data along an alternative path, so the network as a whole keeps operating even while individual parts are broken.
Yes, through multiple-choice questions on Big Idea 4. Typical stems ask which configuration best demonstrates redundancy, how redundancy improves reliability, or which part of a network diagram is a single point of failure.
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