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Red Hat Enterprise Linux Troubleshooting Guide

You're reading from   Red Hat Enterprise Linux Troubleshooting Guide Identify, capture and resolve common issues faced by Red Hat Enterprise Linux administrators using best practices and advanced troubleshooting techniques

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Product type Paperback
Published in Oct 2015
Publisher
ISBN-13 9781785283550
Length 458 pages
Edition 1st Edition
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Author (1):
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Benjamin Cane Benjamin Cane
Author Profile Icon Benjamin Cane
Benjamin Cane
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Benjamin Cane has nearly 10 years of experience in Linux systems administration. His first systems administration role was in 2006. At that time, he worked for a web hosting company supporting thousands of FreeBSD and Linux systems. Afterwards, he joined a managed services company that specialized in managing mission-critical systems. There, he worked his way to the position of a lead systems engineer, providing 24x7 support for highly critical enterprise systems that ran Red Hat Enterprise Linux. Now, Benjamin is a systems architect. He focuses on building High and Continuous Availability environments within the financial services industry. He is also currently a Red Hat Certified Engineer and Certified Ethical Hacker. With his experience in mission-critical environments, he has learned to identify and troubleshoot very complex issues quickly, because often these environments have a low tolerance for downtime. Being able to identify the root causes of very complex systems issues quickly is a skill that requires extensive knowledge of Linux and troubleshooting best practices. In addition to this book, Benjamin writes about Linux systems administration and DevOps topics on his blog at http://bencane.com. He is also the project founder for Runbook (https://github.com/Runbook/runbook), an open source application designed to monitor and automatically resolve infrastructure and application issues.
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Toc

Table of Contents (14) Chapters Close

Preface 1. Troubleshooting Best Practices FREE CHAPTER 2. Troubleshooting Commands and Sources of Useful Information 3. Troubleshooting a Web Application 4. Troubleshooting Performance Issues 5. Network Troubleshooting 6. Diagnosing and Correcting Firewall Issues 7. Filesystem Errors and Recovery 8. Hardware Troubleshooting 9. Using System Tools to Troubleshoot Applications 10. Understanding Linux User and Kernel Limits 11. Recovering from Common Failures 12. Root Cause Analysis of an Unexpected Reboot 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...

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Authors (1)

Profile icon Benjamin Cane
Benjamin Cane
LinkedIn icon Github icon
Benjamin Cane has nearly 10 years of experience in Linux systems administration. His first systems administration role was in 2006. At that time, he worked for a web hosting company supporting thousands of FreeBSD and Linux systems. Afterwards, he joined a managed services company that specialized in managing mission-critical systems. There, he worked his way to the position of a lead systems engineer, providing 24x7 support for highly critical enterprise systems that ran Red Hat Enterprise Linux. Now, Benjamin is a systems architect. He focuses on building High and Continuous Availability environments within the financial services industry. He is also currently a Red Hat Certified Engineer and Certified Ethical Hacker. With his experience in mission-critical environments, he has learned to identify and troubleshoot very complex issues quickly, because often these environments have a low tolerance for downtime. Being able to identify the root causes of very complex systems issues quickly is a skill that requires extensive knowledge of Linux and troubleshooting best practices. In addition to this book, Benjamin writes about Linux systems administration and DevOps topics on his blog at http://bencane.com. He is also the project founder for Runbook (https://github.com/Runbook/runbook), an open source application designed to monitor and automatically resolve infrastructure and application issues.
Read more
See other products by Benjamin Cane

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