>> When it fails, does it fail immediately, or does it take a few seconds
>> before the error shows up?
>>
>> If it fails immediately, it could be a router or firewall blocking
>> something or maybe iptables.
>
> It fails immediately, and soon the error message is gone in the next try.
> That is happened sometimes, say once in seven times ssh.  I don't think
> firewall could work that way.  Am I right?

Yes, I would expect a firewall to either deny (possibly generating the
'no route' error by explicitly denying the connect), or allow it,
every time.

Are there any routers involved, or are both the home and office
machines on the same LAN, in the configuration where you see the
failures?

                                                         - Bluejay Adametz

If you don't climb out on the limb, you may never get the fruit.
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