What is the optimal buffer size and socket size for FileZilla FTP server on a full 45mbps T3?

We just installed a T3/DS3 (full 45mbps) in our organization but our transfer rates on FileZilla server v0.9.25beta have yet to reach above 400-500kbps. The MTU size on the T3 router is set to 4470 bytes, BW is 44210 Kbit, DLY is 200 usec. Encapsulation is PPP.

In FileZilla, the internal buffer size is set to the default of 32768, and the socket buffer size is set to the default of 65536. Should these values be any different to allow the server to open faster up to those connecting?
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alan2938Asked:
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giltjrConnect With a Mentor Commented:
Interesting.  Sounds like something is provisioned incorrectly.
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giltjrCommented:
What is the link speed at the other end?  You have a DS3, but if the other side only has a T1 you will never get more throughput that a T1.

What is the RTT between you and the ftp server?  

Why do you have a MTU of 4470?
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alan2938Author Commented:
The FTP server is on our internal network. The RTT is <1ms.

The MTU setting of 4470 was specified by our T3 provider as the optimal setting. This is a full 45mbps circuit. Do you feel it should be set to something else?
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giltjrCommented:
O.K. maybe I need to ask, where are the ftp clients?  What is the RTT between the server and the clients?  If the ftp clients and server on both on your internal network, then what does the T3 have to do with this?

The speed of the circuit does not effect the MTU. The typical MTU in a LAN today is 1500, or 1492.  An MTU any larger on your WAN link will do nothing, as the the other side of the WAN link is limited to 1500 (or smaller).  Now, having it at 4470 will not cause you any problems, because the routers on either end of the T3 will only get 1500 bytes at a time.  
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alan2938Author Commented:
Our FTP clients are all over the country. We deal primarily with clients in New York city and the surrounding area, but deal with clients from Los Angeles all the time.

The MTU size of the interface connected to the T3 on our firewall is maxed out at 1500. Would it help to set the T3 router MTU size to 1500 so it can talk more efficiently with the firewall, or would it even make a difference?

And what about my original question regarding the buffer and socket size of FileZilla?
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giltjrCommented:
Changing the MTU on the router for T3 will not affect anything.  The major point there is that anything above 1500 will not help, its not going to hurt, because nothing larger that 1500 should be passing through it.

Adjusting the buffer sizes on your side will only help when somebody is sending (put) a file to you.  If somebody is pulling (get) a file from you, it is their window size that effects the performance.

I would also be very careful about tweaking this.  The problem is if you tweak it to allow a customer that has a T3 to get blinding throughput, you could overload a customer that has a 128 Kbps link.  If you know what the slowest link a customer has, you could tweak for that link.  However what I would suggest is that you make sure the OS is setup for sliding windows.  That will help inbound (put) transfers, but you are still at the mercy of the customers for outbound (get) transfers.

Is the 400-500 kbps (you did mean kilo bits per second and not bytes, right?) a combined number or  the best for a single transfer?  If the best for a single transfer, how many other transfers were going on at the same time and what were they getting?
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alan2938Author Commented:
Yes 400-500KBps: kilo bits. The transfer speed kept fluctuating between that range. There was no one else connected to the FTP server at the time, but there was our normal internet chatter that 25 users bring to the scenario, which in our case isn't much.

The slowest connection we deal with is probably a cable modem. We just had a client take a day to put a 9GB file on our server via their office cable modem connection.

When I use Speakeasy to test our line speed, I am averaging a 36-40MBps downstream and have only reached, at most, 14-15MBps upstream. This is from any workstation or server in my network.
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giltjrCommented:
Just wanted to make sure 400-500 KBps is about 3-4 Mbps, which is about what you would typically see from high speed ADLS or Cable connectdion.  

Do you know what the clients bandwidth was when you saw the 400-500 Kbps?

Do you have any bandwidth throttling enabled?  IIRC Filezilla has a option to limit the amount of bandwidth a single transfer can take.  I could be wrong, I used quite a few different ftp servers.

Your speak easy speed is probably normal since Windows desktops really are tuned for high speed inbound data transfsers.  I've tweaked by Windows box and the best I can get on our T3 inbound is about 30 Mbps.  On a Linux box I get 40-43 Mbps in both directions.

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alan2938Author Commented:
I did some troubleshooting with a tech from my T3 service provider yesterday. Of course his line speed matched mine. I placed a 200MB file in his home directory for him to download. The transfer speed maxed out on average of 250kbps. He initiated five more concurrent transfers for a total of six downloads happening simultaneously. All six download speeds were at 250kbps.

So this tells me some interesting information... the entire bandwidth of my T3 seems to work, but no one can initiate a transfer greater than 250kbps for any single connection when pulling files from us.

A speed test I performed on the T3 line yesterday gave me a warning stating "upload compression detected, upload speeds may be effected".

We bought our Cisco 7204 router with a T3/DS3 module new, and all I did was configure IP addresses and a single route to send all traffic out the Serial port connected to the T3. As fas as I know, nothing on my end should be partitioning up the upstream like that. Any thoughts?
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giltjrCommented:
Seems like something is doing bandwidth limitation.  I know that filezilla has the ability to limit how much bandwidth a transfer can use, I also know that Cisco routers can to.

So here is a test, can you test doing a file transfer to/from the file server from the same LAN as the file server is on?

If you get limited to 250 Kbps, then Filezilla is doing the throttling.  If you get "LAN" speed, then the Cisco router is doing it.
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alan2938Author Commented:
It's definitely not Filezilla. An internal test shows transfer speeds approaching 2mbps.
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giltjrCommented:
Umm, it might not be Filezilla, but something is wrong.  If you are doing a file transfer internally you should get way more than 2mbps, unless you have a 15 year old server that is on a 10Mbps Ethernet LAN segment still using hubs.

Assuming a minimum of 100 Mbps Ethernet on a switch you should be able to easily get 70-90 Mbps.
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alan2938Author Commented:
Well, part of your assumption is correct. There are hubs being used within the company but not to connect the servers. I have inherited a network from people who knew little about things, and therefore always purchased the cheapest solutions when needing to grow.

Anyway, it's weird... I was able to upload a file at just under 10mbps, but can't download at greater than 2mbps. This is backwards from the problem that external users are having.
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giltjrCommented:
If you are using Windows and the standard windows ftp client, try adding the option -w:65700 to the ftp command, something like:

     ftp -w:65700 servername

Since you said the server is not connected to a HUB, that  means that someplace there is a HUB connected to either a router or a switch.  I would double check the duplex setting.  I would also double check the speed and duplex settings on the server.


I would have assumed you have mapped out the connectivity between the server and the router with the T3.  If you have not, do so.  Each and every device, what it is, what it is connected to, and if possible how it is configured.
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alan2938Author Commented:
Well, I heard back from a tech at XO who said they haven't actually done speed tests on their lines until I have brought this problem to their attention... and they are getting the same 14mbps transfer rate on all their other DS3 circuits coming out of the same CO as mine.
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alan2938Author Commented:
After a few weeks of getting nowhere with XO, I am going to close this question and award points. I have eliminated all the possible causes of slowdown within my network so it's up to them now. Thanks for everyone's ideas.
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