Implementation method for DNS application gateway based on NAT-PT
A technology of application layer gateway and implementation method, which is applied in the direction of network connection, data exchange network, digital transmission system, etc., and can solve the problems of high processing overhead and complexity.
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[0045] For the convenience of description and understanding later, the format of the DNS message is briefly described below first.
[0046] DNS defines a message format for queries and responses. Table 1 shows the general format of this message.
[0047]
[0048] Table 1
[0049] As shown in Table 1, this message consists of a 12-byte long header and 4 variable-length fields. The identification field is set by the client and returned by the server, and is used by the client to determine whether the response matches the query. The 16bit flag field is divided into several subfields. The following 4 16bit fields indicate the number of entries contained in the last 4 variable-length fields. For query messages, the number of questions is usually 1, while the other 3 items are all 0. Similarly, for a reply message, the answer number is at least 1, and the remaining two items can be 0 or non-zero.
[0050] The format of each question in the questions section is shown in Tabl...
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