7.2. Following Protocol Streams

It can be very helpful to see protocol in the way that the application layer sees it. Perhaps you are looking for passwords in a Telnet stream, or you are trying to make sense of a data stream. Maybe you just need a display filter to show only the packets in a TLS or SSL stream. If so, Wireshark’s ability to follow protocol streams will be useful to you.

Simply select a TCP, UDP, TLS, or HTTP packet in the packet list of the stream/connection you are interested in and then select the Follow TCP Stream menu item from the Wireshark Tools menu (or use the context menu in the packet list). Wireshark will set an appropriate display filter and pop up a dialog box with all the data from the TCP stream laid out in order, as shown in Figure 7.1, “The “Follow TCP Stream” dialog box”.

[Tip]Tip

Following a protocol stream applies a display filter which selects all the packets in the current stream. Some people open the “Follow TCP Stream” dialog and immediately close it as a quick way to isolate a particular stream. Closing the dialog with the “Back” button will reset the display filter if this behavior is not desired.

Figure 7.1. The “Follow TCP Stream” dialog box

ws follow stream

The stream content is displayed in the same sequence as it appeared on the network. Traffic from A to B is marked in red, while traffic from B to A is marked in blue. If you like, you can change these colors in the “Font and Colors” page in the “Preferences” dialog.

Non-printable characters will be replaced by dots.

The stream content won’t be updated while doing a live capture. To get the latest content you’ll have to reopen the dialog.

You can choose from the following actions:

Help
Show this help.
Filter out this stream
Apply a display filter removing the current stream data from the display.
Print
Print the stream data in the currently selected format.
Save as…​
Save the stream data in the currently selected format.
Back
Close this dialog box and restore the previous display filter.
Close
Close this dialog box, leaving the current display filter in effect.

By default data from both directions is displayed. You can select the Entire conversation to switch between both, client to server, or server to client data.

You can choose to view the data in one of the following formats:

ASCII
In this view you see the data from each direction in ASCII. Obviously best for ASCII based protocols, e.g. HTTP.
C Arrays
This allows you to import the stream data into your own C program.
EBCDIC
For the big-iron freaks out there.
HEX Dump
This allows you to see all the data. This will require a lot of screen space and is best used with binary protocols.
UTF-8
Like ASCII, but decode the data as UTF-8.
UTF-16
Like ASCII, but decode the data as UTF-16.
YAML
This allows you to load the stream as YAML.
Raw
This allows you to load the unaltered stream data into a different program for further examination. The display will look the same as the ASCII setting, but “Save As” will result in a binary file.

You can switch between streams using the “Stream” selector.

You can search for text by entering it in the “Find” entry box and pressing Find Next.