Wireshark

http://www.wireshark.org/

The Basics

Wireshark is a packet analysis tool. It allows you to capture packets and analyze them live, or load captures from another session. You can also use its very handy filter functions to look for specific packets - based on destination, target, type, time, payload, etc.

Wireshark has a nice GUI and can show you some amazing things about network traffic. However, Wireshark is also memory-intensive, and is pretty slow on Mac. It's worth it.

Packet Captures

Capturing packets on a network is useful for troubleshooting, but it is also useful for seeing what the network normally looks like.

Take a Capture

Open up Wireshark, pick your network interface, and click the green fin to start the capture.

Capture Settings

You can control many of wireshark's capture options, one nice feature is outputting the capture file in size increments or time increments. As networks get busier, these cap files get pretty large. This is a nice feature to have.

You can also load multiple capture files simultaneously.

Capture Syntax

You can filter packets at the wireless card level, using packet filtering. Specifically, create filters that use the BPF (Berkeley packet filter) syntax.

The BPF syntax consists of primitives and operators.

Primitives consist of qualifiers and an ID.

Example:

dst host 192.168.0.10 && tcp port 80

First, the primitives and the operators:

primitive: dst host 192.168.0.10

operator: &&

primitive: tcp port 80

Now qualifiers and ID portion:

primitive: dst host 192.168.0.10

qualifier: dst

qualifier: host

id: 192.168.0.10

Filtering Packets

If your wireless card and CPU can handle a large amount of traffic, It is usually better to capture everything and use display filters to show different packets, instead of applying capture filters on the capture level. Capture filters are better if you're targeting your capture at a specific range of devices, a specific channel, or particular protocols.

Use filter expression dialogue to create packet display filters.

Operators and Filter Expressions

You can use several comparison operators and logical operators when constructing the display filter.

Comparison Operators:

• equal to
• not equal to
• greater than
• less than
• greater than or equal to
• less than or equal to

Logical Operators:

• and
• or
• xor
• not

Related Pages

Wireshark can be used to analyze network traffic in detail: Wireshark/Traffic Analysis

Wireshark can be used to sniff HTTPS traffic: Wireshark/HTTPS