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I've tried different clients because I thought it was client related. All of them eventually disconnect, or stop transferring files - followed by getting a timeout disconnect. After a reconnect it works again for a bit of time. It is really strange, I can not figure out the reason.

I'm on a Mac, and the server is a VPS running Debian. If you need further information, please ask!

I appreciate any tips, because I'm kinda stuck!

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My guess is that somewhere along the way, there is a loss of connectivity for a while long enough for the SSH-connection to die off. This sounds like a network issue. – Kvisle Oct 17 '11 at 0:01
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4 Answers

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Try running tcpdump at both ends and analyze the results in Wireshark. You should see which packets get stopped and retransmitted: that will help you to debug it.

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Wireshark will give you a "bandwidth graph". Here is an old example from Ethereal days:

alt text

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What is the network like between the mac and server? Is it possible you are having an MTU (transmission unit problem), that is, you are sending a packet that is to big? This can happen with some DSL providers.

  • Greg
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I hear this "guess" all the time but have never seen anyone able to prove it in any way. – djangofan Jun 24 '10 at 21:27
If you're on a connection with a reduced MTU (such as a DSL PPPoE link) and the other end blocks ICMP "destination unreachable / fragmentation needed" messages then you have a PMTU black hole. The situation is common enough that many vendors have added black hole detection to their IP stack: technet.microsoft.com/en-us/library/cc958871.aspx – Gerald Combs Oct 4 '10 at 15:50
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What does ssh -vvv produce when you try to connect to the remote server ? And what are the results of traceroute and ping to your server ?

On the VPS server you could install something like Smokeping to see whether the connection of the server to your IP experiences intermittent problems.

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