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Re: Sudden, unexplained failure of ssh




On 2018-02-22 09:56, mark.paulus@xxxxxxxxxxx wrote:
> I've been running 2.9.x under windows 7 on my 16GB laptop for a long time (probably the 
> last year), when late last week my ssh outbound quit working.  The failure is indicated with 
> this error message:
> 
> ssh: Could not resolve hostname csu6220509.vzbi.com: Non-recoverable failure in name resolution
> 
> I checked the forums, and what I saw seemed to relate to connecting to VM boxes.
> In my case, this is not the cause of the failure.
> This machine is my company provided (and software managed) laptop, so I don't have a 
> lot of control over (in fact, I don't have hardly any control) what gets "pushed" to it.
> However, the one thing that I noticed that seemed to coincide with the failure is that
> the company pushed an "Elastica Reach Agent 1.0.20930.0" to my machine.

Another poorly written cloud "security"/intercept/monitor BLODA app; see:

	https://cygwin.com/faq/faq.html#faq.using.bloda

appears to be interfering with resolving.
Try "cygcheck ssh wget" to see if non-Cygwin non-Windows DLLs are in your PATH,
remove those directories from your Cygwin PATH, and retry to see if that helps.
Use host/nslookup/dig to get the IP address, and retry using that instead of the
host name, to bypass the resolver, and see if that helps.
See if you can add a bypass in the product for ssh and wget, or have your admins
do so, and report the problem to the vendor.

> I thought the issue might have been a version problem, so I updated to the latest 
> Cygwin version
> $ uname -a
> CYGWIN_NT-6.1 TCO10106LKVTAHB 2.10.0(0.325/5/3) 2018-02-02 15:16 x86_64 Cygwin
> 
> That didn't fix the problem.  I've also tried some other utilities,  which are working, 
> such as mobaxterm(Cygwin based), babun(Cygwin based)  and putty.  All those seem to work
> fine.
> 
> Once I determined that it wasn't my actual network stack, I then tried running ssh under
> strace, and now it works.  So, I can use ssh if I use it with strace, but natively by itself
> it continues to get the failure in name resolution.
> 
> Any clues, hints or pointers on how to go about either determining what the problem is, or 
> how to clean it up?
> 
> (I am also seeing the same issue with wget, and strace clears that up also
> $ wget http://linux1.vzbi.com
> --2018-02-22 09:55:38--  http://linux1.vzbi.com/
> Resolving linux1.vzbi.com (linux1.vzbi.com)... failed: Non-recoverable failure in name resolution.
> wget: unable to resolve host address 'linux1.vzbi.com'

You could try running ssh and wget with debugging options to see if that
bypasses the problem similar to running under strace.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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