Re: Slow FTP downloads from behind PIX

["Bill O'Connell" <boconnell () libertycreativesolutions com>]

Many years ago we had a similar problem. Traffic moving one way(I forget if it was uploads or downloads) After weeks of 
troubleshooting, I inspected and replaced the network cable. Turns out 1 wire wasn't making complete contact and the 
slow speed was actually the result of retransmitting bad packets.

Recently we had a similar problem with traffic in both directions. Completely random. We replaced the firewall, server, 
etc. We were running a wireless T1. The internet provider insisted that the connection tested fine. Throughout the 
spring the problem became worse until one (windy) day last week when our connection became unusable. The internet 
provider came out and discovered trees had grown about 1/2 mile away in the path of the wireless tower. Over the spring 
the leaves grew in and on windy days caused havok on the tcp transmissions.

Both incidents taught me never to rule out the lower layers when it comes to networking.

We used packet captures in both cases during the troubleshooting process.

Hope this helps.

Bill

-----Original Message-----
From: firewall-wizards-bounces () listserv cybertrust com [mailto:firewall-wizards-bounces () listserv cybertrust com] 
On Behalf Of Darren Maskowitz
Sent: Wednesday, June 11, 2008 2:08 PM
To: Firewall Wizards Security Mailing List
Subject: [fw-wiz] Slow FTP downloads from behind PIX

I'm having some issues with FTP traffic through our Cisco PIX 515E.
Our corporate FTP server is located outside the firewall, and we recently upgraded the FTP server software. This 
resulted a noticeable increase in the speed uploading files to the server (5 MB/s+). However when attempts were made to 
download files from the server speeds average about 300 KB/s, rapidly fluctuating between 30KB/s and 600 KB/s. 
Downloading the same file to a server outside our firewall resulted in speeds of about 6MB/s.

Looking at the firewall: the default inspection scheme is enabled, and the FTP inspection is turned on. The FTP server 
requires active transfer mode, and everything works, albeit slowly. After turning off FTP inspection connections to the 
FTP server did not work until enabling passive mode, but that didn't change the speeds at all.

I should probably also mention that the PIX is not doing any NAT. All the workstations and servers here have Internet 
routable IP addresses (206.75.x.x).

Any suggestions?

Thanks,
Darren
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