How to resolve stalled inbound data transfers on sftp?

Posted on 2008-06-23
Last Modified: 2010-04-21
A unique problem has presented itself, upon inbound transfers via sftp...once the first 6Kb of a file has been transferred the connection stalls. If left to run, eventually it will complete but only after stalling after every 6Kb of data transferred.

system: running openssh-4.3p2-25.fc6

Data transfer tests with/without IPTABLES running produce same behavior (stalled transfers). Data transfer tests to identical OpenSSH versions on other boxes via Gigabit LAN do NOT produce this behavior (stalled transfers).

Has anyone seen this before or know of a solution?

Question by:mlsevResearch
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LVL 14

Expert Comment

ID: 21850396
What do the error counters in `ifconfig` look like?
Such errors could be caused by duplex mismatches and/or bad cables. Can you try to manually set the port mode for testing purposes?

On Linux, you could use the old `mii-tool` or the new `ethtool` (whatever is installed on your system) to set the port mode manually.

Do you have a 100MBit switch (or configured switch port) available for testing purposes? Gigabit Ethernet over copper sometimes causes very strange issues if the cables are shielded and  I assume you're using shielded cables, right?

Author Comment

ID: 21850548
there are two boxes I'm receiving this error on so I'll paste sanitized output for both ifconfig & mii-tool:

ifconfig -> eth1
 RX packets:12696 errors:1221 dropped:0 overruns:0 frame:1221
 TX packets:4017 errors:0 dropped:0 overruns:0 carrier:0
mii-tool -> eth1
 eth1: negotiated 100baseTx-FD flow-control, link ok

ifconfig -> eth1
 RX packets:54276479 errors:7102653 dropped:0 overruns:0 frame:7102653
 TX packets:89790299 errors:0 dropped:0 overruns:0 carrier:0
mii-tool -> eth1
 eth1: negotiated 100baseTx-FD flow-control, link ok

all gigabit LAN traffic is for, connected to a LinkSys 8-port Gigabit switch

yes, I believe shielded cables are being used
LVL 14

Expert Comment

ID: 21850614
Are these systems connected to the Gigabit switch? If so, mii-tool won't show the correct port settings as mii-tool is too old to know about GiE on copper ;)

OK, but we now know that there are no errors.
Try to switch the speed down to 100MBit/s or use unshielded cables for testing purposes (if available).
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Author Comment

ID: 21850687
the ifconfig output I posted shows both devices have RX errors...which is exactly what's happening.

not able to swap out cables for testing, will look into what port speeds I can set on the switch...

I would argue that it's the switch but with all devices connected to the same switch yet only two in the mix are having RX errors?? That doesn't make sense...
LVL 14

Accepted Solution

agriesser earned 500 total points
ID: 21852935
You're right, sorry. I need to get myself some new glasses really soon...

If all machines connected to this switch would be of the same kind (same network card, same driver, etc.) you could definetly say that the cables are bad for the two machines which have the problem.

But in your case it could be everything (bad cables, buggy drivers, etc.).
Running GiE on the wire is a very delicate task where everything has to play together well.

In my office, f.ex., I needed to configure some ports of our Cisco Gigabit Switch Modules down to 100Mbit/s otherwise I wasn't able to get DHCP leases on them nor was I able to boot via PXE.

Besides that, using no real drivers but just the EEPROM of the NICs, loading software via PXE on Gigabit NICs is much slower than it is on 100MBit/s NICs using the already available cabling.
A month ago, we started to cable a new building and used unshielded CAT-7 cables which proofed the best performance I ever saw when using Gigabit Ethernet over copper. No problems in this building with PXE imaging, etc., it just simply works.

Author Comment

ID: 21855484
agriesser, thanks for the previous responses as well as the latest detailed response. I'm in the process of getting information together concerning the cabling utilized for the GiE set-up to see where we're at...

so hopefully this solution will be solved shortly and points awarded...

Author Closing Comment

ID: 31470316
power-cycle of switch cleared the problems, thanks for all the help
LVL 14

Expert Comment

ID: 21859067
I recently RMA'ed a Linksys 8-port GiBit switch due to some ill effects like you experienced. You should definetly think about replacing this switch...

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