Wireshark-users: Re: [Wireshark-users] capture filter tcp port 20 and port 21
From: Becky Vict <[email protected]>
Date: Mon, 18 Sep 2006 03:40:09 -0700 (PDT)
thank you jaap and ulf.

i had tried this --> tcp port 20 or tcp port 21 and it works beautifully!

ulf, if i use active mode, would my data port be negotiated for every transfer?

thanks.

Ulf Lamping <[email protected]> wrote:


>
> i want to capture ftp download from a server to a client. what is the capture filter to be used at both server and client so i can get only traffic from/to port 20 and port 21?
>
> i tried this --> tcp port 20 and tcp port 21 but no traffic is captured.
>

The correct syntax for what you thought of would be: tcp port 20 or tcp port 21

However, As the data port will often be negotiated (aka varies from transfer to transfer), you'll often won't be able to use a capture filter for this as you won't capture the data portion, see: http://wiki.wireshark.org/FTP

Regards, ULFL
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