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Supernetting

5 minutes 5 Questions

Supernetting, also known as Classless Inter-Domain Routing (CIDR) aggregation, is a method of combining multiple contiguous IP address ranges into a single larger range. This is particularly useful for reducing the size of routing tables, making the routing process more efficient and reducing the overhead associated with maintaining complex routing tables. Supernetting reduces the number of individual entries in a routing table by combining multiple smaller networks with similar network addresses into a single, larger routing entry. This is accomplished by reducing the number of bits used for the network prefix in the subnet mask, effectively merging networks with adjacent address spaces. Supernetting helps conserve IP address space and can be used to optimize route summarization in large networks, improving routing efficiency and reducing administrative overhead.

Guide to Supernetting for CompTIA Network+

What is Supernetting?
Supernetting, also known as Classless Inter-Domain Routing (CIDR), is a technique used in IP address networking management. This method is used to decrease the usage of IP addresses by combining networks with the same initial bits into one network.

Why is Supernetting Important?
Supernetting helps manage and conserve the limited IPv4 addressing space. It aids in reducing the size of routing tables and hence, improves efficiency.

How does Supernetting work?
Supernetting works by combining smaller networks into larger ones. In other words, it's aggregating multiple networks into a single larger network. In order to perform supernetting, one needs to convert the IP addresses to binary format, perform logical OR operation on the network bits and then convert back to decimal form.

Exam Tips: Answering Questions on Supernetting
1. Understand the Binary: Having basic binary conversion skills will help a lot in answering supernetting problems.
2. Practice Problems: Besides understanding how supernetting works, practicing numerous supernetting exercises will help you to answer questions more quickly in the exam.
3. Review Network Basics: Make sure you understand the basics of network addressing, especially the differences among Class A, B and C networks.
4. Understand Subnetting: Supernetting is in essence the opposite process of subnetting. So, having a solid understanding on subnetting will also be beneficial.

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CompTIA Network+ - IP Addressing Example Questions

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Question 1

When supernetting two IPv6 networks, 3000:1000::/32 and 3000:2000::/32, what is the resulting supernet address and prefix length?

Correct Answer: 3000::/31

When supernetting or aggregating two IPv6 networks, we inspect the network portion of the given addresses. In this case, the common portion is '3000' for the higher order 16 bits. As we are combining 3000:1000::/32 and 3000:2000::/32, the new network address starts with 3000. When we look at the third 16-bit block, it is different. This means these two networks can be combined one level up in the hierarchy. Hence, instead of a /32, we end up with a /31 prefix. Hence, the new supernet is 3000::/31. The ‘3000::/32’ and '3000:3000::/32' answers are incorrect because they retain the original /32 subnet mask. This does not represent a supernetting scenario. Answer '3000::/30' is also incorrect because it goes one level too high in aggregating the network.

Question 2

An organization with multiple subnets, each with different CIDR values, wants to optimize routing summarization. Which supernetting solution should they use?

Correct Answer: Create a single aggregate address and mask

The best solution for an organization with multiple subnets and different CIDR values wanting to optimize routing summarization is to 'Create a single aggregate address and mask'. This is known as supernetting, a strategy that allows various small networks to appear as one large network to upstream devices, thus reducing the number of routes that a router must keep in memory. The reason the other answers are incorrect: 'Create individual aggregate addresses for each subnet' would not optimize routing, it would simply replicate the existing situation. 'Remove subnet masks from routing tables' would not be practical or effective since subnet masks are required for IP address recognition and routing. 'Increase the number of subnets' would potentially complicate routing and put additional loads on network infrastructure.

Question 3

Your organization needs to supernet multiple class C networks into a single segment for efficiency. What is the minimum subnet mask that can be used?

Correct Answer: /22

Supernetting, also known as classless inter-domain routing (CIDR), is a method to combine multiple class C networks into a single network. Class C networks typically use a /24 subnet mask (255.255.255.0), meaning they can have up to 256 hosts. But, when superneting class C networks, we want to combine several of these small networks into a larger one, hence we need to have fewer network bits and more host bits in the subnet mask. This is why the /22 subnet mask (255.255.252.0) is the correct answer, as it allows for 1024 addresses, or 4 class C networks. The /24, /26, and /27 options represent a single class C network, a smaller segment of a Class C network, and an even smaller segment of a class C network respectively. Therefore, they can't achieve the purpose of supernetting multiple class C networks.

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