NAT stands for the Network address translation. A NAT device is a modification and reorganization of an IP address space. This space is changed through the network address. There may be issues and limitations regarding this NAT device being used to improve the IP address space. Some of the protocols for the Internet may not be able to complete the function of the NAT device with the computer that you have.
An IPsec is Internet Protocol Security. It allows the user to encrypt certain pieces of data. There are specific modes of operation. One is through the transport mode, and another is through the tunnel mode. The type of traffic that might likely have problems when passing through the Network Address Translation device would be the IPsec.