We have an ftp server behind a firewall and a load balancer. Before, everything was working fine and all our client was able to connect, list and retrieve information without problem.
1- We made a update of the firmware of the load balancer Thursday.
2- In the weekend we got an electric failure and we discover that our secondary link did not relay as expected.
3- So we investigate and found that our DNS did not point to the correct secondary link so we changed it.
After that, some problems appear when using the secondary(207.x.x.x) link with FTP in active mode only (passive mode was working) so we put the DNS back to normal but the problem still continue. At this moment, ftp work correctly on the primary link.
We contact our load balancer provider and he put a persist trigger on port 21 and it fix the problem for almost all client except 2 of them (for those, active and passive do not work for the LS command it hang and we got a "time out").
The weird things is that I create another FTP Server and I tried through the secondary link from the client where it doesn't work and it work on my new server?
On the load balancer, there is two different link :
- The first one (205.x.x.x)(main link) have a C class (255 ip)
- The secondary (207.x.x.x) as 16 ip.
FTP server is IIS. Client is ftp from command line.
FTP fail at the LS time only. We can connect correctly but when we do a LS, we got "DATA connection failed".
If you need more details, just ask. Thanks a lot.