The USG5000 configure NAT originally, intranet server C.C.C.C use public network address pool and address is A.A.A.A. After the change the address, reconfigure, the address pool address used by intranet server C.C.C.C change to be B.B.B.B. After the change find TCP service of C.C.C.C is broken.
When the service is in off-peak hour, use reset firewall session table command, clear the session table. And problem is solved.
(1) Check the configuration, and it is correct.
(2) Use display firewall session to check session table and find C.C.C.C still use A.A.A.A address pool to access to public network session. And this session is C.C.C.C server long-term constant TCP service. So can judge that, because C.C.C.C server continued to send TCP flow, lead to TCP session cannot aging, so even if change configuration, still use the A.A.A.A address pool of session table, leading to service break.