CCNA Subnetting Questions on Reddit | Blog

CCNA Subnetting Questions on Reddit

Subnetting is a crucial skill for anyone pursuing a Cisco Certified Network Associate (CCNA) certification. It requires a deep understanding of IP addressing and the ability to divide a network into smaller subnetworks. In this blog post, we will explore some popular CCNA subnetting questions that have been discussed on Reddit.

Question 1: Subnetting a Larger Network

User: “I have a network with the IP address and need to divide it into four subnets. How do I calculate the subnet mask and the range of IP addresses for each subnet?”

Response: To divide a network into subnets, you will need to borrow bits from the host portion of the IP address. In this case, since you need four subnets, you will need to borrow two bits (2^2 = 4).

The subnet mask can be calculated by adding the borrowed bits to the original network mask. A /24 network has a default mask of, so by adding two bits, the subnet mask becomes (/26).

The four subnets will have the following IP ranges:

  • Subnet 1: –
  • Subnet 2: –
  • Subnet 3: –
  • Subnet 4: –

Question 2: Variable-Length Subnet Mask (VLSM)

User: “Can you explain how Variable-Length Subnet Mask (VLSM) works and provide an example?”

Response: VLSM allows for the allocation of different subnet masks for different subnets within a network. This enables efficient use of IP addresses and better addressing hierarchy.

For example, let’s say you have a network with the IP address, and you need to divide it into two subnets. The first subnet requires 30 hosts, while the second subnet requires 14 hosts.

You can allocate a /27 subnet (32 IP addresses, 30 usable) for the first subnet and a /28 subnet (16 IP addresses, 14 usable) for the second subnet. This way, you optimize the allocation of IP addresses and minimize wasted address space.

Question 3: VLSM and Route Summarization

User: “How does VLSM relate to route summarization and what are the benefits of using it?”

Response: VLSM, as mentioned earlier, allows for the allocation of different subnet masks for different subnets. This capability plays a crucial role in route summarization.

By using VLSM, network administrators can summarize multiple subnets into a single route advertisement. This reduces the number of routes in a routing table, conserves memory and processing resources, and improves network efficiency.

The benefits of using VLSM and route summarization include:

  • Reduced routing protocol overhead
  • Improved routing table scalability
  • Enhanced network performance
  • Reduced potential for routing loops

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