Book Image

CCNA Routing and Switching 200-125 Certification Guide

By : Lazaro (Laz) Diaz
Book Image

CCNA Routing and Switching 200-125 Certification Guide

By: Lazaro (Laz) Diaz

Overview of this book

Cisco Certified Network Associate (CCNA) Routing and Switching is one of the most important qualifications for keeping your networking skills up to date. CCNA Routing and Switching 200-125 Certification Guide covers topics included in the latest CCNA exam, along with review and practice questions. This guide introduces you to the structure of IPv4 and IPv6 addresses and examines in detail the creation of IP networks and sub-networks and how to assign addresses in the network. You will then move on to understanding how to configure, verify, and troubleshoot layer 2 and layer 3 protocols. In addition to this, you will discover the functionality, configuration, and troubleshooting of DHCPv4. Combined with router and router simulation practice, this certification guide will help you cover everything you need to know in order to pass the CCNA Routing and Switching 200-125 exam. By the end of this book, you will explore security best practices, as well as get familiar with the protocols that a network administrator can use to monitor the network.
Table of Contents (24 chapters)
4
Subnetting in IPv4
21
Mock Test Questions
22
Assessments

Rommon or ROM monitor mode

I have already explained how we could get into rommon by using a break command to interrupt the boot sequence and that would take us to ROM's monitor mode. But we only used it to change register settings, and that was very simple.

But what would you do if you come into work on Monday and found the following screen staring you in the face, telling you that it could not find a bootable device.

Look at this screenshot:

You would be like, what in the world? At this moment, you need to take a breath and think, OK, when I left, all was well and everything was copied to NVRAM and backed up to a TFTP server. It could be possible that you changed the registry to boot to rommon by fat finger the keyboard.

So, what you first try is changing the registry to 0x2102 and resetting to see whether it boots fine, and it does not.

What is happening is your IOS got...