Slow authentication via FTP
Hello! I have a perplexing problem for which I would be grateful for some assistance.
We are a small predominantly Windows site with a few Linux machines (Red Hat ES 3) and about 70 Windows Servers (mixture of physical and virtual).
When connecting TO a Linux machine via FTP, authentication is taking about 40 seconds (very slow). The username and password prompts come up instantly. You put in the password, press enter and then it hangs for approx 40 seconds before it eventually connects fine. Transferring files via FTP, once connected, is fast. It's just the authemtication that is slow.
To help the diagnosis, I set up a simple shell script executed 24x7 every 5 minutes by cron, which connects to another linux box via FTP. It records the elapsed time to authenticate.
I have established the following facts:
(1) Authenticating via FTP from Windows to a Windows machine is always instantaneous.
(2) Authenticating via FTP from Windows to a Linux machine is almost always very slow.
(3) Authenticating via FTP from Linux to a Linux machine is almost always very slow
(4) We have occasional periods lasting between 10 and 15 minutes each time, where authenticating via FTP from Linux to a Linux machine is instanteneous. There is no apparent pattern to when these periods occur, but they always last 10 to 15 minutes. For example one day we had 7 of the "fast" periods, another day just 2.
(5) We have 3 Linux machines. When we have one of these "fast" periods, it is fast for all the Linux machines. (2 of the Linux machines are physical, one is virtual).
So there we have it. The evidence suggests to me that the problem is caused by something external to the Linux machines because all the Linux machines seem to be affected (fast or slow) at the same time. We have a proxy server, DNS server and firewalls here, but I'm not a network administrator so I'm not well up on those things.
Any ideas gratefully received - this is one wierd problem where Google has failed to help me!