Troubleshooting functional issues
by Charit Mishra, Yoram Orzach, James H Baxter
Wireshark Revealed: Essential Skills for IT Professionals
- Wireshark Revealed: Essential Skills for IT Professionals
- Table of Contents
- Wireshark Revealed: Essential Skills for IT Professionals
- Credits
- Preface
- 1. Module 1
- 1. Getting Acquainted with Wireshark
- 2. Networking for Packet Analysts
- The OSI model – why it matters
- IP networks and subnets
- Switching and routing packets
- WAN links
- Wireless networking
- Summary
- 3. Capturing All the Right Packets
- Picking the best capture point
- Test Access Ports and switch port mirroring
- Capturing interfaces, filters, and options
- Verifying a good capture
- Saving the bulk capture file
- Isolating conversations of interest
- Using the Conversations window
- Wireshark display filters
- Filter Expression Buttons
- Following TCP/UDP/SSL streams
- Marking and ignoring packets
- Saving the filtered traffic
- Summary
- 4. Configuring Wireshark
- 5. Network Protocols
- The OSI and DARPA reference models
- Transport layer protocols
- Application layer protocols
- Summary
- 6. Troubleshooting and Performance Analysis
- Troubleshooting methodology
- Troubleshooting connectivity issues
- Troubleshooting functional issues
- Performance analysis methodology
- Top five reasons for poor application performance
- Summary
- 7. Packet Analysis for Security Tasks
- 8. Command-line and Other Utilities
- 2. Module 2
- 1. Introducing Wireshark
- 2. Using Capture Filters
- 3. Using Display Filters
- 4. Using Basic Statistics Tools
- Introduction
- Using the Summary tool from the Statistics menu
- Using the Protocol Hierarchy tool from the Statistics menu
- Using the Conversations tool from the Statistics menu
- Using the Endpoints tool from the Statistics menu
- Using the HTTP tool from the Statistics menu
- Configuring Flow Graph for viewing TCP flows
- Creating IP-based statistics
- 5. Using Advanced Statistics Tools
- Introduction
- Configuring IO Graphs with filters for measuring network performance issues
- Throughput measurements with IO Graph
- Advanced IO Graph configurations with advanced Y-Axis parameters
- Getting information through TCP stream graphs – the Time-Sequence (Stevens) window
- Getting information through TCP stream graphs – the Time-Sequence (tcp-trace) window
- Getting information through TCP stream graphs – the Throughput Graph window
- Getting information through TCP stream graphs – the Round Trip Time window
- Getting information through TCP stream graphs – the Window Scaling Graph window
- 6. Using the Expert Infos Window
- 7. Ethernet, LAN Switching, and Wireless LAN
- 8. ARP and IP Analysis
- 9. UDP/TCP Analysis
- Introduction
- Configuring TCP and UDP preferences for troubleshooting
- TCP connection problems
- TCP retransmission – where do they come from and why
- Duplicate ACKs and fast retransmissions
- TCP out-of-order packet events
- TCP Zero Window, Window Full, Window Change, and other Window indicators
- TCP resets and why they happen
- 10. HTTP and DNS
- 11. Analyzing Enterprise Applications' Behavior
- Introduction
- Finding out what is running over your network
- Analyzing FTP problems
- Analyzing e-mail traffic and troubleshooting e-mail problems – POP, IMAP, and SMTP
- Analyzing MS-TS and Citrix communications problems
- Analyzing problems in the NetBIOS protocols
- Analyzing database traffic and common problems
- 12. SIP, Multimedia, and IP Telephony
- Introduction
- Using Wireshark's features for telephony and multimedia analysis
- Analyzing SIP connectivity
- Analyzing RTP/RTCP connectivity
- Troubleshooting scenarios for video and surveillance applications
- Troubleshooting scenarios for IPTV applications
- Troubleshooting scenarios for video conferencing applications
- Troubleshooting RTSP
- 13. Troubleshooting Bandwidth and Delay Problems
- 14. Understanding Network Security
- A. Links, Tools, and Reading
- 3. Module 3
- 1. Welcome to the World of Packet Analysis with Wireshark
- 2. Filtering Our Way in Wireshark
- 3. Mastering the Advanced Features of Wireshark
- 4. Inspecting Application Layer Protocols
- 5. Analyzing Transport Layer Protocols
- 6. Analyzing Traffic in Thin Air
- 7. Network Security Analysis
- 8. Troubleshooting
- 9. Introduction to Wireshark v2
- Bibliography
- Index
If a user is able to connect and set up a TCP session with an application server, but the application does not function otherwise, or function correctly, then, there are a number of areas that can be investigated. These areas can be investigated using a combination of packet-level analysis, error reports, and configuration comparisons with captures and configurations from other users' machines:
- User credentials: The most common reason for specific-user issues with application functionality is the lack of proper credentials, authorization, rights, and so on. This is the first thing to check whether other users are working normally.
- Application settings on the user machine: Some applications require specific configuration files to be placed on a user's machine in a specific location. Applications may also require certain version levels of application-specific utilities, Java, .NET frameworks, and so on. Usually, an application will provide an error message indicating at least the general nature of a configuration problem.
- Application reported errors: You can look for the error code within response packets or on the user screen that may reveal the nature of application errors:
- Differences in web browsers: Some web applications are designed to work with specific browsers (Chrome, Internet Explorer, Firefox, Opera, and so on) and may not work properly or at all on other browsers and there may not be any error messages provided that indicate this is the case. A comparison of the browser type and version with other working users may be revealing.
The causes of network connectivity and application functionality issues can vary widely, so it is impossible to draw a clear roadmap for every possibility. The best approach to successfully address these problems is not to make too many assumptions without proving those assumptions correct with systematic, logical troubleshooting steps, but try to find or create a scenario where the system, or at least part of the system, works properly and compare the appropriate packet-level details of the working environment to the one that doesn't work.
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