computer science

Supernetwork

Supernetwork is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Supernetwork rather than just read about it. In short: A supernetwork, or supernet, is an Internet Protocol (IP) network that is formed by aggregation of multiple networks (or subnets) into a larger network. The new routing prefix for the aggregate network represents the constituent networks in a single routing table entry.

Key takeaways

Supernetwork belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Supernetwork to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Supernetwork from memory before moving on to harder problems.

Reference excerpt

A supernetwork, or supernet, is an Internet Protocol (IP) network that is formed by aggregation of multiple networks (or subnets) into a larger network. The new routing prefix for the aggregate network represents the constituent networks in a single routing table entry. The process of forming a supernet is called supernetting, prefix aggregation, route aggregation, or route summarization. Supernetting within the Internet serves as a strategy to avoid fragmentation of the IP address space by using a hierarchical allocation system that delegates control of segments of address space to regional Internet registries. This method facilitates regional route aggregation. The benefits of supernetting are efficiencies gained in routers in terms of memory storage of route information and processing overhead when matching routes. Supernetting, however, can introduce interoperability issues and other risks.

Overview In IP networking terminology, a supernet is a block of contiguous subnetworks addressed as a single subnet from the perspective of the larger network. Supernets are always larger than their component networks. Supernetting is the process of aggregating routes to multiple smaller networks, thus saving storage space in the routing table, simplifying routing decisions and reducing route advertisements to neighboring gateways. Supernetting has helped address the increasing size of routing tables as the Internet has expanded. Supernetting in large, complex networks can isolate topology changes from other routers. This can improve the stability of the network by limiting the propagation of routing changes in the event of a network link failure. If a router only advertises a summary route to the next router, then it does not need to advertise any changes to specific subnets within the summarized range. This can significantly reduce any unnecessary routing updates following a topology change. Hence, it increases the speed of convergence resulting in a more stable environment.

Protocol requirements Supernetting requires the use of routing protocols that support Classless Inter-Domain Routing (CIDR). Interior Gateway Routing Protocol, Exterior Gateway Protocol and version 1 of the Routing Information Protocol (RIPv1) assume classful addressing, and therefore cannot transmit the subnet mask information required for supernetting. Enhanced Interior Gateway Routing Protocol (EIGRP) supports CIDR. By default, EIGRP summarizes the routes within the routing table and forwards these summarized routes to its peers. Other routing protocols with CIDR support include RIPv2, Open Shortest Path First, IS-IS and Border Gateway Protocol.

Examples A company that operates 150 accounting services in each of 50 districts has a router in each office connected with a Frame Relay link to its corporate headquarters. Without supernetting, the routing table on any given router might have to account for 150 routers in each of the 50 districts, or 7500 different networks. However, if a hierarchical addressing system is implemented with supernetting, then each district has a centralized site as an interconnection point. Each route is summarized before being advertised to other districts. Each router now only recognizes its own subnet and the other 49 summarized routes. The determination of the summary route on a router involves the recognition of the number of highest-order bits that match all addresses. The summary route is calculated as follows. A router has the following networks in its routing table:

192.168.98.0 192.168.99.0 192.168.100.0 192.168.101.0 192.168.102.0 192.168.105.0

Firstly, the addresses are converted to binary format and aligned in a list:

Secondly, the bits at which the common pattern of digits ends are located. These common bits are shown in red. Lastly, the number of common bits is counted. The summary route is found by setting the remaining bits to zero, as shown below. It is followed by a slash and then the number of common bits.

The summarized route is 192.168.96.0/20. The subnet mask is 255.255.240.0. This summarized route also contains networks that were not in the summarized group, namely, 192.168.96.0, 192.168.97.0, 192.168.103.0, 192.168.104.0, 192.168.106.0, 192.168.107.0, 192.168.108.0, 192.168.109.0, 192.168.110.0, and 192.168.111.0. It must be assured that the missing networks do not exist outside of this route. In another example, an ISP is assigned a block of IP addresses by a regional Internet registry (RIR) of 172.1.0.0 to 172.1.255.255. The ISP might then assign subnetworks to each of their downstream clients, e.g., Customer A will have the range 172.1.1.0 to 172.1.1.255, Customer B would receive the range 172.1.2.0 to 172.1.2.255 and Customer C would receive the range 172.1.3.0 to 172.1.3.255, and so on. Instead of an entry for each of the subnets 172.1.1.x and 172.1.2.x, etc., the ISP could aggregate the entire 172.1.x.x address range and advertise the network 172.1.0.0/16, which would reduce the number of entries in the global routing table.

Risks The following supernetting risks have been identified:

Supernetting is implemented in different ways on different routers. Supernetting on one router interface can influence how routes are advertised on other interfaces of the same router. In the presence of supernetting, detecting a persistent routing loop becomes a difficult problem. Adverse impact in heterogeneous routing environments with discontiguous subnets

See also Provider-aggregatable address space Provider-independent address space

References Notes

Bibliography

External links The Supernetting/CIDR Chart IP Address Subnetting Tutorial Supernet Examples and How to Calculate Supernets

Illustrations

Worked examples

Example 1 — a first encounter with Supernetwork

Start with the simplest possible case. Write down what Supernetwork claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Supernetwork before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Supernetwork ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Supernetwork

In research: Supernetwork appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Supernetwork in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Supernetwork is common in secondary-school and first-year university syllabi. It links to neighbouring topics Internet architecture, Internet terminology, Network performance, so understanding it makes those chapters shorter.
In everyday life: Look for Supernetwork outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Supernetwork in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Supernetwork means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Supernetwork out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Supernetwork in simple terms?

Why does Supernetwork matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Supernetwork?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Supernetwork.