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Odd behavior with fiber line

Posted on 2009-04-06
Medium Priority
Last Modified: 2012-05-06
We have a co-lo with our ISP in a weather hardened facility. The link to this facility is via a 100mbit fiber line (approx 11k ft). We have a server, nas device, and firewall at the co-lo.  All Servers are 2k3

I can copy data to the co-lo without issues. When I try to copy the data back to the office I get "network connection timed out". We have tried copying the files via windows explorer and FTP with the same results. The connection will drop with < 50MB transfered. Single or multiple files.

Odd thing is internet traffic and downloads are uneffected. Only thing we are having problems with is copying data back from the co-lo. Files can be transfered fine between the equipment at the co-lo and to the equipment at the co-lo, but when we try to copy it back across the fiber it drops.

Tranceivers at both ends of the fiber have been replaced, We have connected the fiber ends direct to the server at the co-lo and to a laptop at the office with the same result. Tests on the fiber showed everything was good.

Any ideas or suggestions greatly appreciated. We are stumped currently. :(
Question by:fsjavan32
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Expert Comment

ID: 24083452
Are you _sure_ all tranceivers have been replaced?  I.E.  Is the fiber really a 11k foot fiber that doesn't pass through any switches controlled by your ISP?

This could very well be their problem.
Have you tried copying from multiple devices at the co-lo?

And did you check error counters on your switches at both ends of the fiber?

It may be that you are getting errors and heavy drops when the bit rate is great enough.
The effect on internet traffic might be to slow it down, whereas the impact on a large file transfer is more severe.

If there's a problem with fiber itself, there could be receive errors / loss of sync / or loss of carrier  events   on the interface attached to the one failing.

It's also a good idea to use MRTG to graph number of packets if possible  (both directions on both link)

If your graph shows the interface at one side is SENDING  a good number of packets but the other side isn't RECEIVING a good number,  then  that would be an indicator of loss.

Author Comment

ID: 24087975
Yes I have tried both devices at the co-lo.  I did not see any abnormal packet errors on my switch. We did bypass the switch to test if that was causing a problem. To my knowledge they do not have any devices between the transeiver and my firewall.

In using etheral to capture packets I have discovered  an issue. Duplicate ACK
We have tested transfering files directly through the fiber without any devices (switches/firewalls) between the computer/server. I am going to do more research on the duplicate ACK, but is that more of an issue with the fiber or bad configuration?


Author Comment

ID: 24088178
Response from the ISP on the fiber question.
Yes I'm sure the fiber is 11,000 feet I shot it yesterday with the OTDR and it was like 11,803 feet both fibers.  The trancievers have both been replaced with brand new units.
The only switch that it goes to is your sonic wall.


Author Comment

ID: 24098667
Installed Qcheck at the office and at the Co-lo, UDP stream packet loss is < 0.5%. TCP throughput is varied. Anywhere from 5Mbps to 70Mbps. Running Etheral to capture the packet there is a lot of duplicate ACK packets when doing the TCP throughput test.

Accepted Solution

fsjavan32 earned 0 total points
ID: 24111871
The ISP replaced the J/E-PSW-FX-02 (SM) with a chassi unit and the problem is now fixed. We are not sure why 2 of those tranceivers would not work but a full chassi unit would.

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