Learning Action in publishing DNS part 4

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Learning Action in publishing DNS part 4 Chapter 33.1.1 Header SectionThe 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 thelength 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 Meaning (bytes) 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 3.2) Table 3.1: The meaning of individual control fields Error Code Numeric Error Description Value 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 3.2: Answer result codes (the Rcode field) 49DNS Extension3.1.2 Zone SectionThe zone section defines the zone that will be updated. One DNS Update request can only be usedfor updating one zone, i.e., the zone section only authorizes one record to be used.The section consists of three parts: • ZNAME: zone name • ZTYPE: must be SOA • ZCLASS: zone class (IN)3.1.3 Prerequisite SectionThe Prerequisite section contains a set of RR records that must exist on the primary master serverin a particular zone at the moment of delivering an Update packet. We have five choices(alternatives) in the prerequisite section: • There must be at least one RR record of a given NAME and TYPE (RR set exists, value independent). The prerequisite section contains one record of a given NAME and TYPE that is expected in the zone. Other items are of no importance, therefore, we will use RDLENGTH=0, RDATA remains empty, CLASS=NY, TTL=0. For example, an A type record is requested with the domain name of aaa.company.com and with any RDATA that exists in the domain. • There must be a set of RR records of a given NAME and TYPE in the zone, with the right side corresponding to the right side of the Update packet records (RR set exists, value dependent). The order of records is of no importance. The section contains a set of RR records of a given NAME and TYPE, and RDATA, TTL=0, CLASS is specified in the zone section. For example, a zone containing the following records is requested: mail.company.com. A 195.47.11.11 www.company.com. A 195.47.11.12 company.com. MX 10 mail.company.com • The zone does not contain any RR record of a given NAME and TYPE (RR set does not exist). The section contains one RR record of a given NAME and TYPE, RDLENGTH=0, RDATA is empty, CLASS=NONE, TTL=0. For example, the zone requested does not contain any type A record with the mail.company.com domain name. • The zone must contain at least one record of a given NAME and TYPE defined in the zone section (Name is in use). The section contains one RR record of a given NAME, RDLENGTH=0, RDATA is empty, CLASS=ANY, TYPE=ANY, TTL=0. For example, the zone requested contains at least one record, the domain name of which contains the company.com field, i.e., it is not an empty zone.50 Chapter 3 • There are no RR records of any TYPE with a given NAME (The name is not in use). The section contains one RR record of a given NAME, RDLENTGHT=0, RDATA is empty, CLASS=NONE, TYPE=ANY, TTL=0. For example, the requested zone does not contain any record of the domain name that would contain the company.com string, i.e., it is an empty zone.3.1.4 Update SectionThe update section contains RR records that are to be added to or removed from the zone. Fourdifferent changes are possible: • Add RR records: The update section contains several records. Records of a given NAME, ...