I was trying to load up a server with bulk data using rsync, and I kept getting this:
ssh_dispatch_run_fatal: Connection to 10.1.2.3 port 22: message authentication code incorrect
10.1.2.3 is the (internal) IP address of the server I'm copying from. It failed so many times, I fell back on my old friend mirror.pl, but that wasn't really satisfactory, because rsync is much faster and better.
I tried googling, but no-one seemed to have an answer for this. The real problem was that I didn't actually understand the problem. So I invested some time in trying to understand, without any luck - all I could see was "it isn't working".
So I fell back on another tried and tested diagnostic. What did I change most recently?
And the answer was, the gigabit ethernet switch. I had the from-server on a Netgear consumer-grade switch that I'd just bought, and the to-server on another one of the same. I wonder if that could be the problem? Although Netgear stuff is usually very good.
So I put both servers on the same switch; the old 5-port gigabit switch I bought eons ago. And that seems to have done something ... the error message is now
"rsync error: error in rsync protocol data stream"
So I checked my own notes. Last time this happened, I added -e '/usr/bin/ssh' to the rsync command and that fixed it, so I'll try that now.