IP subnetting is one of the main trouble spots on the CCNA exam. To do well on the CCNA exam, you must be skilled at:
- Interpreting the terminology surrounding subnetting
- Remembering which math process to use to find a particular answer
- Mastering the use of a particular math process to find the answer
- Applying the related IP addressing and routing concepts while also working with the math
- Working through the analysis and math very quickly on the exam
There are also some possible trouble spots, especially in these five technical topics:
- IP Subnetting and Addressing: The single most challenging technology topic for most candidates.
- Spanning Tree Protocol (STP): In real life, most people have STP enabled, and it works, and there is no need to pay much attention to it. As a result, even people who already work in networking jobs typically learn little about STP on the job.
- Access Control Lists (ACLs): ACLs act as a basic programming language that can be applied to packets flowing through a router for the purpose of filtering some packets (discarding the packets). Implementing ACLs requires mastery of the packet headers, an understanding of packet flow, and an understanding of the logic behind the commands.
- Open Shortest Path First (OSPF): OSPF is the most complex IP routing protocol included in CCNA. While CCNA only examines the basics of OSPF, its underlying operation differs so much from RIP and EIGRP that it requires a little more thought.
- Packets and Flows: Particularly for those brand new to the networking world, the details of frames, packets, segments, their headers, the flow of packets with end user data, the related overhead processes, all the related terminology, and how it all interacts, can be a big challenge.
The exam environment and question types also pose some big challenges. In particular, time pressure exists in almost every Cisco exam. Like all Cisco exams, the CCNA exam does not allow you to skip a question and go back later, so there's a tendency to take extra time when unsure. The exam includes three particularly time-consuming problem types: Sims, Simlets, and Testlets. While a time goal of 1 minute per multichoice question time budget is reasonable, these other questions typically require 4-8 minutes each-but each counts as 1 question from the overall count of the number of questions. And your speed at finding the answers to subnetting questions will impact whether you feel much time pressure.
Finally, two question types-Sims and Simlets-require you to have practiced and become comfortable with typing commands on a Cisco router or switch CLI as if you were configuring and monitoring real equipment. As a result, most CCNA candidates need hands-on experience before tackling the ICND1, ICND2, and CCNA exams.