Ethereal-users: Re: [Ethereal-users] TCP flow filtering

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From: Guy Harris <gharris@xxxxxxxxx>
Date: Wed, 19 Oct 2005 13:51:07 -0700
Narayanan Vydianathan (nvydiana) wrote:

What does "Follow TCP stream " option do in Analyze menu ?

Creates a filter that accepts packets between the endpoints (address/port) in the selected packets, filters the display, and, in the process of doing that, puts the payload into the "Follow TCP Stream" window.

If I identify a TCP syn packet , can I trace all the packtes belonging to this flow using the above option.

Yes - although note that the filter just checks for endpoint identifiers, so if there's *more than one* connection between those endpoints (i.e., a connection is opened, traffic goes between them, it's closed, and then another connection is opened), you'll see traffic for both of them.

I am interested in finding holes in a given flow (out of order /retransmmision) issues in a flow. Do I have to write custom filters to do this?

For out-of-order packets and retransmissions, turn on the "Analyze TCP sequence numbers" preference for TCP, and the TCP dissector will flag those. "tcp.analysis.out_of_order" matches frames transmitted out of order, and "tcp.analysis.retransmission" matches frames that are TCP-layer retransmissions. (You needn't use "Follow TCP Stream" for that.)