Understanding TCP SYN ACK and discards

I'm have a bit of a problem running an application though my firewall. I THOUGHT I had all of the correct ports open, but am still having difficulty. It's supposed to just be using FTP (p21) Can someone shed some light on the following?

69.157.73.126 - WAN IP 192.168.1.5 - LAN IP 226.232.132.19 - EX HOST IP

discard from 192.168.1.5 port 1172 to 226.232.132.19 port 49371 TCP SYN ACK (default)

discard from 226.232.132.19 port 49371 to 69.157.73.126 port 35526 TCP SYN (Sequence number not within expected range, possible attack )

discard from 192.168.1.5 port 1172 to 226.232.132.19 port 49371 TCP SYN ACK (default)

discard from 226.232.132.19 port 49371 to 69.157.73.126 port 35526 TCP SYN (Sequence number not within expected range, possible attack )

discard from 192.168.1.5 port 1172 to 226.232.132.19 port 49371 TCP SYN ACK (default)

Thanks!

Reply to
Frank G
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Could it be you're using passive FTP? FTP is one of the protocols that use more than one connection (for details see [1]). To allow FTP to traverse NATing firewalls you need connection tracking to match the second (data) connection to the first (control) connection.

[1]
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cu 59cobalt
Reply to
Ansgar -59cobalt- Wiechers

Reply to
Frank G

You also need port 20. (FTP uses two ports) For active FTP from the server side to the client you need The FTP server will also need to talk to ports on the client >1023

Being you mention port 21, you may be runing in passive mode, but you would still need ports .1023 to be available.

Reply to
Dana

All of the above is only true for active mode. In passive mode it's the client initiating the data connection, and port 20/tcp is not involved then. Instead the data connection is established from a port > 1023 on the client to a port > 1023 on the server.

cu

59cobalt
Reply to
Ansgar -59cobalt- Wiechers

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