CCNA
Cisco Certified Network Associate certification resources
Subnetting Based on Host Requirements
There are two ways to approach a subnetting problem: start from how many subnets you need, or start from how many hosts each subnet needs to support. This guide covers the second approach, host-based subnetting, which flips the usual left-to-right bit-borrowing process on its head and starts from the right instead. The Core Trade-Off Subnetting...
Creating 4,000 Subnets from a /8 Prefix
Some organizations need far more subnets than a typical /24-based design provides. A small ISP allocating a separate subnet to each of 4,000 clients is a realistic example: with a /8 network to work with, there’s plenty of host-portion room to borrow from. This guide works through the full process, including five completely worked examples...
Subnetting Example with a /16 prefix – Exclusive How To Guide
In many situations, we require a large number of subnets. For example, the class B network address 130.20.0.0 has a default mask of 255.255.0.0 or /16 Prefix. So, this address has 16 network bits in the network portion and 16 host bits in the host portion. The 16 bits in the host portion are available...
Classless Subnetting Examples: Two Fully Worked Problems
Classless subnetting, made possible by CIDR (Classless Inter-Domain Routing) since its introduction in 1993, lets an administrator borrow bits from any position in the host portion of an address, rather than being restricted to classful boundaries like /8, /16, or /24. This guide works through two complete subnetting problems on the same base network, step...
Classful vs. Classless Addressing: What’s the Difference?
Classful and classless addressing describe two different ways to structure an IPv4 address. Classful addressing came first, in the early internet of the 1980s. It used fixed Class A, B, and C ranges. That rigid structure eventually led to serious IPv4 address exhaustion. CIDR arrived in 1993 and introduced classless addressing instead, allowing flexible prefixes...
Collision Domains and Broadcast Domains Explained
Understanding where a collision domain ends and where a broadcast domain ends is one of the most fundamental spatial-reasoning skills in networking, and it’s tested constantly on the CCNA exam through topology diagrams. This guide covers both concepts precisely, works through a single consistent topology example for each, and covers the real problems that happen...
Introduction to Subnetting: How and Why to Divide a Network
Subnetting lets a network administrator divide a large network into smaller, more manageable sub-networks by borrowing bits from the host portion of an IP address. Rather than running one enormous flat network, subnetting adds a third level to the addressing hierarchy, network, subnetwork, and host, giving administrators far more control over how a network actually...
Ping and Traceroute: The Essential Network Troubleshooting Toolkit
Ping and traceroute are the first tools most network engineers reach for when something isn’t working. Both rely on ICMP, but they answer different questions: ping tells you whether a destination is reachable at all, while traceroute maps out exactly which hops a packet passes through along the way. This guide covers both in depth,...
ICMPv6 Neighbor Discovery: RS, RA, NS, and NA Messages Explained
ICMPv6 does considerably more than its IPv4 counterpart. Beyond basic error reporting, it absorbs an entire protocol’s worth of functionality through the Neighbor Discovery Protocol (NDP), four distinct message types working together to replace ARP, handle address resolution, and drive SLAAC. This guide covers each of the four NDP message types, how they interact, and...
Internet Control Message Protocol (ICMP) Explained
IP is deliberately unreliable: it has no built-in mechanism to report when something goes wrong. That’s exactly the gap the Internet Control Message Protocol (ICMP) fills. It doesn’t make IP more reliable, it doesn’t retransmit or guarantee delivery, but it does report problems back to the source, which is what makes tools like ping and...