Raspbian Jessie Static IP Config

Question

I followed this guide to create a static IP for my Raspberry Pi running Raspbian Jessie. The static IP is running but my router still lists the old IP address for the Raspberry Pi. I also am no longer able to ssh into my Pi; when I try to ssh using the hostname, the ssh connection times out. On the other hand, when I try to ssh to the static IP, I receive the following error:

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@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
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IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
<finger print>.
Please contact your system administrator.
Add correct host key in <path to known_hosts file> to get rid of this message.
Offending RSA key in <path to known_hosts file>:21
RSA host key for <raspberry pi static ip> has changed and you have 
requested strict checking.

How do I fix this?

Answer 1

NEVER delete a known_hosts file, because it will wipe out all the seen keys! And a MitM attack against you will be much easier. Open it with text editor and replace/delete *a single string starting with a hostname. After a hostname there's a key, so either update the key or delete just one string and connect to a new key+address pair

Answer 2

You get the warning because you changed the IP address. This is security issue as it could mean you are the subject of a man in the middle attack. To fix the problem you can edit the old entry from the known_hosts file. The file is located in the /home/pi/.ssh directory. You can open it in the editor of your choice and delete its contents.

As for your router seeing the old address that will eventual be removed automatically.