Wireshark

http://www.wireshark.org/

Background

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.

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

The filters use 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:

dst host 192.168.0.10 && tcp port 80
-----------------------------  ---  -------------
primitive                operator  primitive

Now the qualifier and id portion:

dst      host        192.168.0.10
----     -------- -------------------------
qualifier qualifier      ID