Book Image

Red Hat Enterprise Linux Troubleshooting Guide

By : Benjamin Cane
Book Image

Red Hat Enterprise Linux Troubleshooting Guide

By: Benjamin Cane

Overview of this book

Red Hat Enterprise Linux is an operating system that allows you to modernize your infrastructure, boost efficiency through virtualization, and finally prepare your data center for an open, hybrid cloud IT architecture. It provides the stability to take on today's challenges and the flexibility to adapt to tomorrow's demands. In this book, you begin with simple troubleshooting best practices and get an overview of the Linux commands used for troubleshooting. The book will cover the troubleshooting methods for web applications and services such as Apache and MySQL. Then, you will learn to identify system performance bottlenecks and troubleshoot network issues; all while learning about vital troubleshooting steps such as understanding the problem statement, establishing a hypothesis, and understanding trial, error, and documentation. Next, the book will show you how to capture and analyze network traffic, use advanced system troubleshooting tools such as strace, tcpdump & dmesg, and discover common issues with system defaults. Finally, the book will take you through a detailed root cause analysis of an unexpected reboot where you will learn to recover a downed system.
Table of Contents (14 chapters)
13
Index

Hypothesis


Now that we understand how packets to 192.168.33.11 are routed, we should adjust our previous hypothesis to reflect that the route of 192.168.33.11 to enp0s3 is not correct and is causing our issue.

Essentially, what is happening (and we see this via tcpdump) is that, when the database server (192.168.33.12) receives a network packet from the blog server (192.168.33.11), it arrives on the enp0s8 device. However, when the database server is sending reply packets (SYN-ACK) to the web application server, the packets are being sent out via the enp0s3 interface.

Since the enp0s3 device is connected to the 10.0.2.0/24 network, it seems that the packet is being rejected (RESET) by another system or device on the 10.0.2.0/24 network. Most likely, this is due to the fact that this is a prime example of asynchronous routing.

Asynchronous routing is where a packet arrives on one interface but is replied to on another. In most network configurations, this is denied by default, but in some cases...