Book Image

Network Analysis using Wireshark Cookbook

By : Yoram Orzach
Book Image

Network Analysis using Wireshark Cookbook

By: Yoram Orzach

Overview of this book

Is your network slow? Are your users complaining? Disconnections? IP Telephony problems? Video freezes? Network analysis is the process of isolating these problems and fixing them, and Wireshark has long been the most popular network analyzer for achieving this goal. Based on hundreds of solved cases, Network Analysis using Wireshark Cookbook provides you with practical recipes for effective Wireshark network analysis to analyze and troubleshoot your network. "Network analysis using Wireshark Cookbook" highlights the operations of Wireshark as a network analyzer tool. This book provides you with a set of practical recipes to help you solve any problems in your network using a step-by-step approach. "Network analysis using Wireshark Cookbook" starts by discussing the capabilities of Wireshark, such as the statistical tools and the expert system, capture and display filters, and how to use them. The book then guides you through the details of the main networking protocols, that is, Ethernet, LAN switching, and TCP/IP, and then discusses the details of application protocols and their behavior over the network. Among the application protocols that are discussed in the book are standard Internet protocols like HTTP, mail protocols, FTP, and DNS, along with the behavior of databases, terminal server clients, Citrix, and other applications that are common in the IT environment. In a bottom-up troubleshooting approach, the book goes up through the layers of the OSI reference model explaining how to resolve networking problems. The book starts from Ethernet and LAN switching, through IP, and then on to TCP/UDP with a focus on TCP performance problems. It also focuses on WLAN security. Then, we go through application behavior issues including HTTP, mail, DNS, and other common protocols. The book finishes with a look at network forensics and how to search and find security problems that might harm the network.
Table of Contents (23 chapters)
Network Analysis Using Wireshark Cookbook
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Configuring protocol preferences


Configuring protocol preferences provides us with capabilities to change the way that Wireshark captures and presents common protocols. In this recipe we will learn how to configure the most common protocols.

Getting ready

  1. Go to Preferences under the Edit menu, and you will see the following window:

  2. Click on the + sign on the left side of the protocols, and a protocol list will be opened. Under the protocol list you will find the common and lesser-common protocols. In this part we will talk about the common configurations, and we'll get into protocol details in the protocols chapters that is, Chapter 7, Ethernet, LAN Switching, and Wireless LAN, to Chapter 14, Understanding Network Security.

How to do it...

In this recipe, we will talk about the following basic protocols (basic means that they are used everywhere, not that they are simple):

  • IPv4 and IPv6

  • TCP and UDP

Configuring of IPv4 and IPv6 Preferences

When you choose to configure the IPv4 or IPv6 parameters, you will get the following window:

The parameters that you may change are:

  • Decode IPv4 ToS field as DiffServ Field: the original IP protocol came out with a field called Type Of Service (ToS), for enabling the IP quality of service through the network. In the early 90s the Differentiated Services (DiffServ) standard changed the way that an IP device looked on this field. Unchecking this checkbox will show this field as in the original IP standard.

  • Enable GeoIP lookups: GeoIP is a database that enables Wireshark to present IP addresses as geographical locations. Enabling this feature in IPv4 and IPv6 will enable this presentation. This feature involves name resolutions and can therefore slow down packet capture in real time.

Configuring TCP and UDP

In UDP, there is not much to change. A very simple protocol, with a very simple configuration. In TCP on the other hand, there are some parameters that can be changed.

Most of the changes you can do in the TCP preferences are in the way that Wireshark dissects the captured data.

  • Validate the TCP checksum if possible: in some NICs, you may see many "checksum errors". This is due to the fact that TCP Checksum offloading is often being implemented on some NICs. The problem here might be that the NIC actually adds the checksum AFTER Wireshark captures the packet, so if you see many TCP checksum errors, the first thing to do will be to disable this checkbox and verify that this is not the problem.

  • Analyze TCP Sequence numbers: this checkbox must be checked for Wireshark to provide TCP analysis, which is one of its main and most important features.

  • Relative Sequence Numbers: when TCP opens a connection, it starts from a random sequence number. When this checkbox is checked, the Wireshark will normalize it to "0", so what you will see are not the real numbers, but numbers starting from "0" and increasing. In most of the cases the relative numbers are much easier to handle.

  • Calculate conversations timestamps: When checking this checkbox, the TCP dissector will show you the time since the beginning of the connection in every packet. This can be helpful in cases of very fast connection when times are critical.

How it works...

Using the Protocols feature from the Preferences menu adds more analysis capabilities to the Wireshark software. Just be careful here to not add too many capabilities that will slow down the packet capture and analysis.

There's more...

You can get more information on GeoIP at http://wiki.wireshark.org/HowToUseGeoIP.