Tham khảo tài liệu 'learning publishing dns in action ebook_4', công nghệ thông tin, hệ điều hành phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 3 Header Section The header section like DNS Query header section contains identification in the first two bytes ID field followed by two bytes for control fields and there are four two-byte fields for the length of the individual sections each length is 2 bytes ZOCOUNT Number of records in the Zone section PRCOUNT Number of records in the Prerequisite section UPCOUNT Number of records in the Update section ADCOUNT Number of records in the Additional data section Field Length bytes Meaning ID 16 Message identification is copied into the answer QR 1 0 for DNS Update request 1 for DNS Update answer DNS Update does not use other check bits. Opcode 4 Value is 5 DNS Update copied from the request into the answer Z 7 Reserved for future use should be zero 0 in all requests and responses Rcode 4 Response code in an answer unidentified in a request see Table Table The meaning of individual control fields Error Code Numeric Value Error Description NOERROR 0 No errors. FORMERR 1 Message format error the name server is unable to interpret the request. SERVFAIL 2 An internal server error has occurred when processing the message for example OS error or the forwarding timeout exceeded. NXDOMAIN 3 The name that should exist does not exist. NOTIMP 4 The name server does not support the specified Opcode. REFUSED 5 The name server refuses to execute the message for example due to security reasons. YXDOMAIN 6 Some name that should not exist does exist. YXRRSET 7 Some RR records that should not exist do exist. NXRRSET 8 Some RR records that should exist do not exist. NOAUTH 9 The server is not an authority for that particular zone. NOTZONE 10 A name used in the Prerequisite or Update section is not within the zone denoted by the Zone section. Table Answer result codes the Rcode field 49 DNS Extension Zone Section The zone section defines the zone that will be updated. One DNS Update request can only be used for updating one zone . the zone section .
