To prevent an adversary from having time to break your cryptosystem, you need to refresh your keying material. When you replace the SAs on one system, the SAs must also be replaced on the communicating system.
When replacing security associations, remove the old keys before you add new keys. Use the flush command in ipseckey command mode to remove the old keys. Then add the new keying information.
# ipseckey > flush > add esp spi …