topic Re: NAT and FTP problem in Network Security

NAT and FTP problem

randyclark — Mon, 11 Mar 2019 11:54:30 GMT

I have a NATed client trying to FTP to a server on the Internet. The server is blocking the FTP connection becuase it sees the private address of my client. Is there a setting on the firewall to prevent this from happening?

Re: NAT and FTP problem

ajagadee — Mon, 28 Jan 2008 17:39:38 GMT

What is the NATing device. Is this a Pix/ASA Firewall or router. If this is a Pix/ASA, do you have Fixup configured. Can you post your configuration along with details on what is the ip address of the FTP Client and FTP Server.

Regards,

Arul

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Re: NAT and FTP problem

randyclark — Mon, 28 Jan 2008 18:39:23 GMT

The NATing device is an ASA 5520. The client is being NATed. I'm not sure about the server.

Re: NAT and FTP problem

srue — Mon, 28 Jan 2008 19:17:00 GMT

make sure you have ftp inspection enabled in your global policy.

inspect ftp

if that doesn't work, please post what happens when you ftp to this server and exactly how it 'fails'.

Re: NAT and FTP problem

cisco24x7 — Mon, 28 Jan 2008 19:24:46 GMT

As a test, on the ASA do this:

fixup ftp protocol 21

nat (inside) 1 0 0

global (outside) 1 interface

access-list test permit ip any any log

access-group test in interface inside

access-group test in interface outside

Now from a host inside the ASA, perform

a ftp connection. I have an ftp server

on the Intenet. If you give me your public

IP address, I can add it to my checkpoint

security policy so that you can test connecting to it.

CCIE Security

Re: NAT and FTP problem

randyclark — Mon, 28 Jan 2008 21:14:33 GMT

This is what is happening on the client side. It's not using the standard port 21 but port 1021.

connecting to 149.149.15.100:1021

xxxxxxx

Host type (S):UNIX (standard)

PASV

227 Entering Passive Mode(149,149,15,100,59,23)

connecting to 149.149.15.100:15127

!Conntection failed 149.149.15.100-connection refused

!connect error 0

PORT 172,20,46,74,7,132

500| I won't open a connection to 172.20.46.74(only to 198.146.198.101)

!Failed "port"

Re: NAT and FTP problem

cisco24x7 — Mon, 28 Jan 2008 22:28:29 GMT

fixup protocol ftp 1021

As a security person, I am very suprised that

people still use FTP these days. Not only

the protocol is insecure, you will run into

issues like this.

I noticed that ftp server box is a Unix box.

If that is the case, why not use SecureFTP

(sFTP). sFTP is a component of sshd daemon

which is very secure. You can configure

it to run at AES256-cbc with sha-1 and allow

ssh outbound access. Everything will be ok

after that.

This is 2008, not 1998. FTP and TFTP should

be banned due to its inherent weak security by nature. TFTP should be replaced by Secure

Copy (scp).

CCIE Security

Re: NAT and FTP problem

randyclark — Wed, 30 Jan 2008 13:49:58 GMT

I don't know why they are still using FTP. It's another college who has the FTP server. Maybe they fear change. I'll try the fixup ftp 1021 command and post the results.

Inspect is the new command on the ASA for fixup correct?