FTP issue over DSL(very chronic)

Unanswered Question

Hi experts.

We are running a DSL connection at a few of our locations.

These locations all have a Cisco 871 connected to a Netopia DSL modem and we have tunnels on this 871 connecting it to a hub location.Hub has a cisco 7206 VXR.

We are facing a problem where in when we try to send files via FTP from the spoke locations to the hub site, they some times get stuck and are not transferred through. This usually happens when these files are big. We then have to switch over to a backup connection to transfer these files and shutdown the DSL.

Please can someone advise what could possible be the issue and how we can fix this. I have also posted part of the 871 config.

Thanks in anticipation,

Imran.

I have this problem too.
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Joseph W. Doherty Thu, 02/14/2008 - 17:19

I don't have any first hand experience with the 871, but from the description of your problem, what I'm wondering is whether the 871 is just being crushed by bandwidth of the large download. Do you have any recorded performance stats before the stoppage? What's the maximum DSL downlink bandwidth? What version and feature set are you using?

Perhaps one way to easily confirm whether it's the bandwidth push causing the issue, shape the outbound rate on your 7200 to one Mbps and see if the problem still occurs. If not, start to ramp up until it breaks again.

If it is bandwidth related, try to optimize every aspect the impact of the configuration options of your 871s. This might include items such as trying, if supported, AES instead of 3DES, reordering ACL sequences (most hit first), removing IP accounting, removing ACL logging, buffer tuning, insuring debug mode is off, console logging off, using longer load-interval, changing scheduler ratios, insure all packets are not being fragmented within your GRE/IPSec tunnels, etc.

Running the most current patch IOS release might preclude you from memory leaks and other issues that might only arise under extreme stress.

Joseph W. Doherty Mon, 02/18/2008 - 17:08

If MTU is off in such a way that packets are being fragmented, I believe that might increase CPU load of the router fragmenting the packets but shouldn't affect your destination router much receiving them. (I also notice you're using tcp adjust-mss which should avoid framentation on TCP flows.)

You really want to gather some additional stats from the 871 as the download ramps up and should try metering the traffic to see if that makes a difference.

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