Both Network Address Translation (NAT) and Port Address Translation (PAT) are configured on the C1750 router and both work normally.
However, after 6 to 12 hours of operation, the PAT fails. No new PAT session can be established.
Power cycling the router makes PAT work again, but the problem occurs again after several hours.
To resolve this issue, refer to the First Fixed-In Version column in Cisco bug ID CSCdv25204. This provides a list of Cisco IOS Software versions that do not exhibit this problem.
To download these Cisco IOS Software versions, refer to Cisco Downloads.