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SSH Session Disconnecting

Hello Everybody,

I am becoming increasingly frustrated with an issue that I've seen span MANY different devices (both routers and switches, with varying IOSes installed).

The problem I am seeing is when I am scrolling through the logs on a router or switch (by holding the spacebar), my session will disconnect.  This happens using SSH in both PuTTY and SecureCRT.

I have seen this same issue occur when performing a show tech, as well as when holding spacebar while scrolling through a show int status on some of our Nexus switches with many, many ports configured.

I have checked the available resources after signing back in, and each time available resources have been sufficient.  Has anyone else experienced this issue or perhaps know of a cause/resolution?



Phillip Remaker
Cisco Employee
Cisco Employee

Hello Jason!  Sorry to hear about the problem.  This sort of issue needs a TAC case, because there is clearly a software bug.  What platform and software version are you using? 

CSCsd98525 describes a similar issue, limited only to IOS.  CSCsz83570 also describes a similar issue. 

A workaround is to force the use of SSHv1 until you apply the software fix.

Also, at least for CSCsz83570, setting "term len 0" tends to prevent the disconnect, as does switching to 3DES instead of AES.   This bug is triggered by TCP congestion and those two workarounds avod the issue.  Swicthing to SSHv1 does as well.

Thanks very much for that informatin Phillip.  This is something that I've seen at the last 3 businesses I've worked for.  With hardware ranging from 3750 switches to 3800 routers, and Nexus devices.

I will look into those bugs later this evening.

I've had the same experience with multiple types of hardware and software versions for years.  It seems to be related to the rate of info flowing to the console.  A show tech w/term len 0 usually will trigger it.

Not sure if it can be fixed, I can of learned to pace myself when on a remote session...

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