Changing your Kerberos passwords
NAT
If your machine is behind a NAT router, you will be unable to use that system to change your Kerberos password. The Kerberos password-changing mechanism will only work for systems with a public IP address. If your system's IP address is something like 192.168.x.x then you might be behind such a router. If you do try to change your password from behind a NAT, you may get a error message something a long the lines of Failed decrypting request.
Changing your Kerberos password from the command line
Linux and Mac OS X users can use the kpasswd utility to change their Kerberos password from the command line;
kpasswd principal