11.2.3 CHANGED-ADDRESS
The CHANGED-ADDRESS attribute indicates the IP address and port where
responses would have been sent from if the "change IP" and "change
port" flags had been set in the CHANGE-REQUEST attribute of the
Binding Request.
11.2.4 CHANGE-REQUEST
The CHANGE-REQUEST attribute is used by the client to request that
the server use a different address and/or port when sending the
response.