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PInkFloyd's avatar
PInkFloyd
Icon for Nimbostratus rankNimbostratus
Mar 23, 2021

Passive FTP using FTP profile

Hi Community,

 

I have an F5 Big-IP 16.0.1.1 running on AWS with a FTP server behind running vsftpd.

The idea is balance passive ftp publically. So, clients should hit public IP of the F5 for passive ftp. This scenario is running perfectly without an FTP profile, just a tcp profile (all ports) and the option pasv_address on the ftp server pointing to the public IP address of the F5. But I need to have this working with the FTP profile in order to implement extra security for FTP on the F5.

 

I've tried to implement FTP passive load balancing using official documentations like (https://techdocs.f5.com/en-us/bigip-15-0-0/big-ip-local-traffic-manager-implementations/load-balancing-passive-mode-ftp-traffic.html ) , but no matter what combination or configuration is implemented on the F5 & the ftp server, if I have the ftp profile the message ("passive mode refused") is always received after request PASV and only works if I use this for internal passive ftp, meaning that I not configure a "pasv_address" on the ftp server, and the client that request the connection is in the same Lan than the F5 & ftp server, resolving everything internally.

 

As a said, i've tried a lot of combinations and settings on the F5 and ftp servers, but nothing works. Could someone give me a little of guidance here?

 

Thanks in advance.

AWS
BIG-IP
cloud
ftp
passive
profile
security
  • Daniel_Wolf's avatar
    Daniel_Wolf
    Icon for MVP rankMVP
    Mar 23, 2021

    Can you share your config? This works for me out of the box.

    I am using the default FTP profile.

    root@(ffive01)(cfg-sync Standalone)(Active)(/Common)(tmos)# list ltm profile ftp ftp
ltm profile ftp ftp {
    app-service none
}

    I have a virtual listening on port 21 and the following iRule attached.

    when SERVER_CONNECTED {
  FTP::port 40000 40200
}

    And this is my vsftpd.conf

    listen=NO
listen_ipv6=YES
xferlog_enable=YES
secure_chroot_dir=/var/run/vsftpd/empty
anonymous_enable=NO
local_enable=YES
write_enable=YES
chroot_local_user=YES
user_sub_token=$USER
local_root=/home/$USER/ftp
pasv_min_port=40000
pasv_max_port=40200
userlist_enable=YES
userlist_file=/etc/vsftpd.userlist
userlist_deny=NO

    No issues at all, see tcpdump.

     

    • PInkFloyd's avatar
      PInkFloyd
      Icon for Nimbostratus rankNimbostratus
      Mar 24, 2021

      Hi Daniel,

      First thanks for share this information with me.

      I duplicate your configs, just to prevent missconfigurations.

      Here is my config.

      admin@(TESTING01)(cfg-sync Standalone)(Active)(/Common)(tmos)# list ltm profile ftp ftp
ltm profile ftp ftp {
    app-service none
}

      FTP config

      listen=NO
listen_ipv6=YES
local_enable=NO
anonymous_enable=YES
write_enable=NO
anon_root=/ftp/test
xferlog_enable=YES
dual_log_enable=YES
log_ftp_protocol=YES
vsftpd_log_file=/ftp/logs/vsftpd.log
xferlog_file=/ftp/logs/xferlog.log
pasv_min_port=40000
pasv_max_port=40200
anon_umask=022
banner_file=/etc/vsftpd/banner.txt

      VIP config ( config not listed below has been kept as default)

      source address: any
destination address: any
Service Port: 21 ftp
Protocol: tcp
ftp profile: ftp
Vlan and Tunnel traffic: all VLANs and tunnels
Source Address Translation: auto map
Address translation: enabled
port translation: enabled
Default Pool: FTP POOL

      I've created an FTP monitor that retrieves a file on the ftp server , attach it to the ftp pool and its working ok.

      The issue start when a remote source (whitelisted to access) connects to the FTP using the F5 public ip, everything looks good until the remote source request PASV

      if my ftp pool member is configured with it Public IP, the error recieved after PASV is 

      421 Service not available, remote server has closed connection
Passive mode refused.

      If my FTP pool member is configured using its private IP, the client receives ( "227 Entering Passive Mode (private VIP ip , Ephemeral Port ")

      obviously can not be resolved by the remote source.

      I downloaded an Irule that i found in this forum, that preserve ephemeral ports and i modified it to sent (no matter what) the public IP of the F5 when pasv is requested ( keeping the ephemeral port as it is) but again "passive mode refused" )

      I've tried another combinations like use "pasv_address" on the ftp server, pointing to the F5 public & private IP, but only works if I point to Public Ip Address of the F5 and remove the ftp profile from the VIP.

  • Daniel_Wolf's avatar
    Daniel_Wolf
    Icon for MVP rankMVP
    Mar 24, 2021

    Did you add the iRule from my example too?

    Do you really have destination address set to any?

    I would compare my lab config again later today, to see if I did any further "magic" on the vsftp, or maybe I have a setting in my FTP Client that is important... I set that up 3 years ago and never touched it ever since, except of installing Linux updates.

    • Daniel_Wolf's avatar
      Daniel_Wolf
      Icon for MVP rankMVP
      Mar 24, 2021

      I checked this further and I cannot find any difference. I checked if I missed something in my vsftpd.conf... nope.

      Your VS config seems OK, too. Can you check for the destination 0.0.0.0:0 (any) and the iRule? That seems off....

      In my Wireshark capture it looks like this:

      vsftp server ----> floating self-IP >> ftp.passive.ip==<IP address of the vsftp server>
virtual server ----> client >> ftp.passive.ip==<IP address of the F5 virtual>

      So the value for ftp.passive.ip get's updated and replaced properly.

      I tried with FileZilla and WinSCP, no special config required there either. Just works.

      • PInkFloyd's avatar
        PInkFloyd
        Icon for Nimbostratus rankNimbostratus
        Mar 25, 2021

        Yes I added your Irule.

        Are you using a single interface ?? are you ftp setup residing on AWS ? Because my test lab includes a single interface on the F5 with a EIP(AWS) attached.

        so, I realized that the FTP profile is just translating the IP address configured as pasv_address on the ftp server to the address configured on the vip as "destination address" only when ( no pasv_address is configured in the ftp, configured pointing public ip of ftp server or if its configured using private IP address), but if pasv_address is manually configured to be the Public ip address of the F5, nothing is translated and the client received 

        421 Service not available, remote server has closed connection
Passive mode refused.

        but, if I leave the ftp server pasv_address option pointing to the Public ip address of the F5 , remove the ftp profile on the VIP and change service port to "all ports" works perfectly.

        so, seems to me (maybe i'm completely wrong) that the ftp profile is unable to translate the received pasv_address (no matter is received) to the Public IP that the F5 has assigned for AWS( EIP)

        make sense?

  • kimbn's avatar
    kimbn
    Icon for Nimbostratus rankNimbostratus
    Oct 31, 2022

    It's just my personal opinion right here but as for me, I strongly believe that you need to get more information about this free secure ftp server because it seems to me that you won't face this problem using that one there. If you still have any issues, you can read more reviews on the Internet as well.

  • richard_polyak's avatar
    richard_polyak
    Icon for Altocumulus rankAltocumulus
    Feb 15, 2024

    Daniel - I have had issues setting up FTP virtual servers on F5 versions. My solution is the following:

     

    ltm profile ftp prof_ftp_mydefault {
        app-service none
        defaults-from ftp
        inherit-parent-profile enabled.   <--------- Enabling this allowed the VS to use passive FTP.

     

    Thx

    Rich