Shulou(Shulou.com)06/02 Report--

When the firewall does mapping, it generally does not do two-way mapping of ports, but is restricted in, and out is not restricted, unless there are other special security requirements.

In addition:

A public network IP can be mapped to multiple private network IP, which can be distinguished by port. For example, all the services of exchange are published through a public network IP.

On a certain type of firewall in cisco, multiple ports of a private network IP cannot correspond to multiple public network IP. This mapping method is not supported. For example, 25 and 443 of 1.121 correspond to two public network IP respectively, which is not possible. After reading the official release documents, it is true that this model is not supported.

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