Why does the nonat gets removed when we enable access on tcp level.

[Hemakumar Sampath]

       What makes the CISCO ASA to remove nonat when we enable access in tcp or udp level

[Jennifer Halim]

Nonat only supports IP level within the access-list, and will remove the NAT statement if you have TCP or UDP ports configured.

Here is the command for your reference:

http://www.cisco.com/en/US/docs/security/asa/asa82/command/reference/no.html#wp1756533

(quoted from the above:

NAT. NAT exemption is not the same as policy NAT; you cannot specify the port addresses)