I keep getting these errors showing up in the log from sshd:
error: kex_exchange_identification: banner line contains invalid characters
I finally tracked them down and understand the nonsense that
is happening:
For historical reasons (having to do with butthead IT people
at work deciding outgoing sshd should be blocked by firewall),
I listen on the https port (443) as well as the normal 22 on my
sshd at home.
Apparently "helpful" web browsers on my android devices and
wot-not decide they ought to probe connections to see if https
is possible before falling back to http, so they all probe
my ssh daemon :-).
The error has been happening forever, but the latest sshd
now logs it (it previously just ignored it).