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Date:      Thu, 4 Jan 1996 20:45:19 -0500 (EST)
From:      "Jonathan M. Bresler" <jmb@FreeBSD.ORG>
To:        security@FreeBSD.ORG
Cc:        questions@FreeBSD.ORG
Subject:   PASV, FreeBSD does!  sunos fails.
Message-ID:  <Pine.BSF.3.91.960104203530.9211U-100000@Aspen.Woc.Atinc.COM>

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my new employer is a large sun shop.  sparcs and ncd's everywhere.  we 
also have a firewall to pass through.   

NONE of the suns have an ftp client that supports PASV.

FreeBSD 2.1R does. ;)

tomorrow i will be recompiling FreeBSD 2.1R ftp code on sunos 4.1.3 and 
porting it to sunos 5.4

score two points, gentlemen.   i believe that a one line message will 
appear everytime the 'new' ftp is run.

	"This application ported from FreeBSD 2.1"


ps	what is PASV??

	ftp uses two tcp connections, one for commands and one for data transfers
(files and ls output for instance).  the ftp client (some high port) 
connects to the server (port 21)  to create the command connection.  the 
server (port 20) connects to the client (high port) to return the data.   

	some firewalls filter out incoming tcp connections (ip flags has 
SYN set, ACK not set).  so ftp does not work.

	enter PASV.  the client creates both the command and the data 
connections to the server.  all packets from the server have both SYN and 
ACK set.

Jonathan M. Bresler        FreeBSD Postmaster         jmb@FreeBSD.ORG
play go. ride bike. hack FreeBSD.--ah the good life 
i am moving to a new job.                 PLEASE USE: jmb@FreeBSD.ORG

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