When the IV runs through all of its unique values, the IV value
repeats. When the IV value repeats, using the same master key and
the repeated IV value to encrypt data means that the encryption
is the same as an encryption previously used on other data.
Change the Master Key before
the system runs out of unique encryptions to prevent the firewall
from using the same encryption (master key and IV value combination)
on more than one piece of sensitive data. Unique encryption combinations
should never be repeated or reused.