1. 12012-08-31 DNS Summer Days 2012DNSRFCUnbound

2. 2 : @ttkzw : 24365 MSP DNS 19972006 BIND4, BIND8, djbdns, BIND9 NSD, Unbound Unbound Unbound/NSD DNS( 3. 3 DNS 4. 4 DNS RFC 1034 DOMAIN NAMES CONCEPTS AND FACILITIES RFC 1035 DOMAIN NAMES IMPLEMENTATION AND SPECIFICATION RFC 5. 5 RFC DNSSEC DNSSECRFC DNSSEC 6. 6 7. 7RFC IETFInternet Engineering Task Force RFC"Request for Comments" RFCRFC 8. 8RFC RFCRFCNetwork Working Group R. Arends Request for Comments: 4033 Telematica Instituut Obsoletes: 2535, 3008, 3090, 3445, 3655, 3658, R. Austein 3755, 3757, 3845 ISC Updates: 1034, 1035, 2136, 2181, 2308, 3225, M. Larson 3007, 3597, 3226 VeriSignCategory: Standards Track D. MasseyRFC Colorado State University S. Rose NIST March 2005 RFC DNS Security Introduction and Requirements Status of This Memo This document specifies an Internet standards track protocol for the 9. 9RFC RFC "ERATTA" RFC"obsoletes" RFCRFC RFC RFC 1034RFC 2181 10. 10RFC RFC 1796 "Not All RFCs are Standards" RFC Infomational Experimental Standard Track Proposed Standard Draft Standard Internet Standard Historic 11. 11: Standard Track Proposed Standard Draft Standard RFC 6410201110"Internet Standard" Internet Standard STD xxx 12. 12: BCP Non-Standards Track Experimental Infomational Historic Best Current Practice BCP xxx 13. 13 RFCThe key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. RFC 2119 / BCP 14 "Key words for use in RFCs to Indicate Requirement Levels" RFC 14. 14 MUST REQUIREDSHALL MUST NOT SHALL NOTSHOULDRECOMMENDED SHOULD NOT NOT RECOMMEDED MAY OPTIONAL 15. 15RFC RFC Editor http://www.rfc-editor.org/ IETF TOOLS http://tools.ietf.org/html/ RFC JPRS DNS http://jprs.jp/tech/ DNSRFC DNSSEC http://dnssec.jp/ DNSSECRFC 16. 16 17. 17DNS2RFC RFC 1034 DOMAIN NAMES CONCEPTS AND FACILITIES RFC 1035 DOMAIN NAMES IMPLEMENTATION AND SPECIFICATION 18. 18RFC 1034DOMAIN NAMES - CONCEPTS AND FACILITIES DOMAIN NAMES CONCEPTS AND FACILITIES DNS 19. 19RFC 1035DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION DOMAIN NAMES IMPLEMENTATION AND SPECIFICATION DNS 20. 20 DNS example.jp.IN SOA ns.exampele.jp. .. example.jp.IN NS ns.example.jp. com jp ns.example.jp. IN A192.0.2.1 exampleexample co ns www 21. 21RFC 1034RFC 1035 DNSRFC 1034RFC 1035 RFC DNSARPANETThe Internet INCS, CH, HS CH $ dig TXT CH version.bind. 22. 22RFC 1034RFC 1035 RFC 1034RFC 1035 RFC RFC 1034RFC 1035 RFC 10341035RFC RFC 2181 "Clarications to the DNS Specication"DNSRFC 23. 23RFC 10341035RFC RFC 1123 Requirements for Internet Hosts -- Application and Support RFC 1982 Serial Number Arithmetic RFC 2181 Clarications to the DNS Specication RFC 2308 Negative Caching of DNS Queries (DNS NCACHE) RFC 3425 Obsoleting IQUERY RFC 4343 Domain Name System (DNS) Case Insensitivity Clarication RFC 5452 Measures for Making DNS More Resilient against Forged Answers RFC 5936 DNS Zone Transfer Protocol (AXFR) RFC 5966 DNS Transport over TCP - Implementation Requirements 24. 24DNS RFC 1982 / PS RFC 4343 / PS Serial Number Arithmetic Domain Name System (DNS) Case Insensitivity ClaricationRFC 1034 / STD 13DOMAIN NAMES - CONCEPTS AND RFC 2181 / PSFACILITIES Clarications to the DNS RFC 5452 / PS Specication Measures for Making DNS More Resilient against RFC 1035 / STD 13DOMAIN NAMES - Forged AnswersIMPLEMENTATION AND SPECIFICATIONRFC 2308 / PS Negative Caching of DNS RFC 5936 / PS Queries (DNS NCACHE)DNS Zone Transfer RFC 1123 / STD 3Protocol (AXFR) Requirements for Internet Hosts -- Application and Support RFC 3425 / PS Obsoleting IQUERYRFC 5966 / PS DNS Transport over TCP - Implementation Requirements 25. 25RFC 1034 198711: Paul Mockapetris 26. 26RFC 1034 1. STATUS OF THIS MEMO 2. INTRODUCTION 3. DOMAIN NAME SPACE and RESOURCE RECORDS 4. NAME SERVERS 5. RESOLVERS 6. A SCENARIO 7. REFERENCES and BIBLIOGRAPHY 27. 27RFC 1034 DNS 28. 281. STATUS OF THIS MEMO1. RFCDNS RFC 1035 29. 292. INTRODUCTION2. 2.1. The history of domain names 2.2. DNS design goals DNS 2.3. Assumptions about usage 2.4. Elements of the DNS DNS 30. 302. INTRODUCTION2. DNSDNS 31. 313. DOMAIN NAME SPACE and RESOURCE RECORDS3. 3.1. Name space specications and terminology 3.2. Administrative guidelines on use 3.3. Technical guidelines on use 3.4. Example name space 3.5. Preferred name syntax 32. 323. DOMAIN NAME SPACE and RESOURCE RECORDS3. 3.6. Resource Records 3.7. Queries 3.8. Status queries (Experimental) 3.9. Completion queries (Obsolete) 33. 33 3 example.jp.IN SOA ns.exampele.jp. .. example.jp.IN NS ns.example.jp. com jp ns.example.jp. IN A192.0.2.1 exampleexample co ns www 34. 343.1. Name space specications and terminology3.1. com jp exampleexample co ns www 35. 353.1. Name space specications and terminology3.1. "com" 0 63 com jp exampleexample co null ns www 0 36. 363.1. Name space specications and terminology3.1. ) "www", "example", "jp", ""com jp exampleexample co ns www 37. 373.1. Name space specications and terminology3.1. "www"16"3 77 77 77" null com jp 0 www.example.jp.exampleexample co3 77 77 77 8 65 78 61 6d 70 6c 65 2 6a 70 0 ns www 255 38. 383.1. Name space specications and terminology3.1. RFC 4343 "Domain Name System (DNS) Case Insensitivity Clarication" 39. 393.1. Name space specications and terminology3.1. "." www.example.jp. com jp exampleexample co www.example.jp.""ns www 40. 403.1. Name space specications and terminology3.1. www.example.jp. com jp exampleexample co ns wwwwww 41. 413.1. Name space specications and terminology3.1. com jp "." exampleexample co "." www.example.jp ns www FQDNFully Qualied Domain Name 42. 423.1. Name space specications and terminology3.1. FQDNFully Qualied Domain Name : www.example.jp RFC 1594 FYI on Questions and com jp Answers - Answers to Commonly asked "New Internet User" Questionsexampleexample co 5.2 What is a Fully Qualied Domain Name? ns www RFC 1983 Internet Users Glossary Fully Qualied Domain Name (FQDN) 43. 433.2. Administrative guidelines on use3.2. DNS 44. 443.3. Technical guidelines on use3.3. DNS RR 45. 453.4. Example name space3.4. ||+---------------------+------------------+| | |MILEDU ARPA| | || | | +-----+-----+| +------+-----+-----+ || | | || |BRL NOSC DARPA| IN-ADDR SRI-NIC ACC| +--------+------------------+---------------+--------+ | ||| |UCI MIT |UDEL YALE | ISI ||+---+---+ || | | LCS ACHILLES +--+-----+-----+--------+|| || ||XX A CVAXA VENERA Mockapetris 46. 463.5. Preferred name syntax3.5. ARPANET RFC 952 DOD INTERNET HOST TABLE SPECIFICATION RFC 1123 Requirements for Internet Hosts -- Application and Support RFC 1123 63 47. 473.6. Resource Records3.6. 48. 483.6. Resource Records 3.6. comjp exampleexampleco ns wwwRRsexample.jp.IN SOA ns.exampele.jp. .. RRsexample.jp.IN NS ns.example.jp.ns.example.jp. IN A192.0.2.1 49. 493.6. Resource Records3.6. owner RR type 16 A, CNAME, HINFO, MX, NS, PTR, SOA class 16 IN(the Internet system), CH(the Chaos system) 50. 503.6. Resource Records3.6. TTL RR32 TTLRR RFC 2181 Clarications to the DNS Specication "8. Time to Live (TTL)" : 0 : 2147483647 (2^31 - 1) 1TTL0 RDATA 51. 513.6.1. Textual expression of RRs3.6.1. RRs RR RR1 example.com. 172800 IN NS a.iana-servers.net. example.com. 3600 IN SOA dns1.icann.org. (hostmaster.icann.org.2012080872 7200 3600 1209600 3600 ) RR example.com. 172800 IN NS a.iana-servers.net. RR example.com. 172800 IN NS a.iana-servers.net.172800 IN NS b.iana-servers.net. 52. 523.6.1. Textual expression of RRs3.6.1. RRs RR TTL,, TTL TTL INTTL RR RDATA RRRDATA 53. 533.6.2. Aliases and canonical names3.6.2. CNAME CNAME CNAMERRRDATA CNAME RR CNAMERR 54. 543.6.2. Aliases and canonical names3.6.2. RFC 2181 Clarications to the DNS Specication "10.1. CNAME resource records" CNAME CNAME ("canonical name")"alias name" CNAME IN CNAME 55. 553.7. Queries3.7. DNS RR4 opcode4 56. 563.7. Queries3.7. 4 Question Answer RR Authority RRanswer SOA RR Additional RR RR 57. 573.7.1. Standard queries3.7.1. QNAME QTYPE QCLASS RR 58. 583.7.2. Inverse queries (Optional)3.7.2. () RFC 3425 Obsoleting IQUERY 59. 594. NAME SERVERS4. 4.1. Introduction 4.2. How the database is divided into zones 4.3. Name server internals 60. 60 4 example.jp.IN SOA ns.exampele.jp. .. example.jp.IN NS ns.example.jp. com jp ns.example.jp. IN A192.0.2.1 exampleexample co ns www 61. 614.1. Introduction4.1. 62. 624.2. How the database is divided into zones4.2. 63. 634.2. How the database is divided into zones4.2. 2 examplejp com jp RFC 2181 Clarications to the exampleexample co DNS Specication "6. Zone ns www Cuts" 64. 644.2.1. Technical considerations4.2.1. 4 com jp example example co sub nswww ns www"glue" 65. 654.2.2. Administrative considerations4.2.2. NS RRsRRs NSRRs 66. 664.3. Name server internals4.3. 67. 674.3.1. Queries and responses4.3.1. RFC 1035 QTYPE, QCLASS, QNAME 68. 684.3.1. Queries and responses4.3.1. 69. 694.3.1. Queries and responses4.3.1. 70. 704.3.2. Algorithm4.3.2. 71. 714.3.3. Wildcards4.3.3. "*"RRs RR 72. 724.3.4. Negative response caching (Optional)4.3.4. () The method is that a name server may add an SOA RR to the additional section of a response when that response is authoritative. RFC 2181 Clarications to the DNS Specication "7.1. Placement of SOA RRs in authoritative answers" SOA additionalauthority 73. 734.3.4. Negative response caching (Optional)4.3.4. () RFC 2308 Negative Caching of DNS Queries (DNS NCACHE) RFC 10348 - Changes from RFC 1034 optionalRFC 2308must AuthoritySOAMUST SOAMUST 74. 744.3.5. Zone maintenance and transfers4.3.5. RFC 5936 DNS Zone Transfer Protocol (AXFR)AXFR 75. 755. RESOLVERS5. 5.1. Introduction 5.2. Client-resolver interface - 5.3. Resolver internals 76. 76 5 example.jp.IN SOA ns.exampele.jp. .. example.jp.IN NS ns.example.jp. com jp ns.example.jp. IN A192.0.2.1 exampleexample co ns www 77. 775.1. Introduction5.1. 78. 785.2. Client-resolver interface5.2. - 79. 795.3. Resolver internals5.3. 80. 806. A SCENARIO6. 81. 817. REFERENCES and BIBLIOGRAPHY7. 82. 82RFC 1035 198711: Paul Mockapetris 83. 83RFC 1035 1. STATUS OF THIS MEMO 2. INTRODUCTION 3. DOMAIN NAME SPACE AND RR DEFINITIONS 4. MESSAGES 5. MASTER FILES 6. NAME SERVER IMPLEMENTATION 7. RESOLVER IMPLEMENTATION 8. MAIL SUPPORT 9. REFERENCES and BIBLIOGRAPHY 84. 84RFC 1035 DNS 85. 851. STATUS OF THIS MEMO1. 86. 862. INTRODUCTION2. 2.1. Overview 2.2. Common conguration 2.3. Conventions 87. 872.1. Overview2.1. 88. 882.2. Common congurations2.2. Local Host| Foreign |+---------+ +----------+ | +--------+| | user queries | |queries | ||| User|-------------->||---------|->|Foreign || Program | | Resolver | | | Name || || Server | | |Resolver|| files | ||||Foreign | | Resolver| | Server | | | Name | | || Server || |Resolver|| files | || ||| | queries | |Foreign | | | | Name | +------------------|--| Server |maintenance responses | +--------+ 92. 922.3. Conventions2.3. 93. 932.3.1. Preferred name syntax2.3.1. ::= | " " ::= | "." ::= [ [ ] ] ::= | ::= | "-" ::= | ::= any one of the 52 alphabetic characters A through Z in upper case and a through z in lower case ::= any one of the ten digits 0 through 9 94. 942.3.1. Preferred name syntax2.3.1. RFC 1123 RFC 952 DOD INTERNET HOST TABLE SPECIFICATION RFC 1123 Requirements for Internet Hosts -- Application and Support 63 95. 952.3.2. Data Transmission Order2.3.2. 96. 962.3.3. Character Case2.3.3. RFC 4343 "Domain Name System (DNS) Case Insensitivity Clarication" 97. 972.3.4. Size limits2.3.4. 63 255 TTL 32 UDP 512 98. 983. DOMAIN NAME SPACE AND RR DEFINITIONS3. RR 3.1. Name space denitions 3.2. RR denitions RR 3.3. Standard RRs RRs 3.4. ARPA Internet specic RRs InternetRRs 3.5. IN-ADDR.ARPA domain IN-ADDR.ARPA 3.6. Dening new types, classes, and special namespaces 99. 99 3 example.jp.IN SOA ns.exampele.jp. .. example.jp.IN NS ns.example.jp. com jp ns.example.jp. IN A192.0.2.1 exampleexample co ns www 100. 1003.1. Name space denitions3.1. null0 20663 255 101. 1013.2. RR denitions3.2. RR 102. 1023.2.1. Format3.2.1. 1 1 1 1 1 10 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+| |/ //NAME /| |+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+|TYPE |+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+| CLASS |+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+|TTL|| |+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+| RDLENGTH|+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|/ RDATA // /+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 103. 1033.2.1. Format3.2.1. NAME TYPE RR TYPE2 CLASS RR CLASS2 104. 1043.2.1. Format3.2.1. TTL 32 RDLENGTH RDATA 16 RDATA 105. 1053.2.1. Format3.2.1. "SOA records are always distributed with a zero TTL to prohibit caching." RFC 2181 Clarications to the DNS Specication "7.2. TTLs on SOA RRs" TTL00TTLSOA 106. 1063.2.2. TYPE values3.2.2. TYPETYPEvalue meaningA 1 a host addressNS2 a host addressCNAME 5 the canonical name for an aliasSOA 6 marks the start of a zone of authorityWKS 11a well known service descriptionPTR 12a domain name pointerMX15mail exchangeTXT 16text strings 107. 1073.2.3. QTYPE values3.2.3. QTYPE QTYPEquestion QTYPETYPE QTYPE"MAILB""MAILA"QTYPE value meaningAXFR252 A request for a transfer of an entire zone* 255 A request for all records 108. 1083.2.4. CLASS values3.2.4. CLASSCLASS value meaningmnemonicsIN1 the InternetCS2 the CSNET class (Obsolete)CH3 the CHAOS classHS4 Hesiod 109. 1093.2.5. QCLASS values3.2.5. QCLASS QCLASSquestion QCLASSCLASSQCLASSvalue meaningmnemonics* 255 any class 110. 1103.3. Standard RRs3.3. RRs 111. 1113.3.1. CNAME RDATA format+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+/ CNAME // /+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+where:CNAME A which specifies the canonical or primaryname for the owner. The owner name is an alias.CNAME RRs cause no additional section processing, but name servers maychoose to restart the query at the canonical name in certain cases. Seethe description of name server logic in [RFC-1034] for details. 112. 1123.3.9. MX RDATA format+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+|PREFERENCE |+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+/ EXCHANGE// /+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+where:PREFERENCEA 16 bit integer which specifies the preference given tothis RR among others at the same owner. Lower valuesare preferred.EXCHANGEA which specifies a host willing to act asa mail exchange for the owner name.MX records cause type A additional section processing for the hostspecified by EXCHANGE. The use of MX RRs is explained in detail in[RFC-974]. 113. 1133.3.11. NS RDATA format+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+/ NSDNAME // /+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+where:NSDNAME A which specifies a host which should beauthoritative for the specified class and domain.NS records cause both the usual additional section processing to locatea type A record, and, when used in a referral, a special search of thezone in which they reside for glue information. 114. 1143.3.12. PTR RDATA format+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+/ PTRDNAME/+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+where:PTRDNAMEA which points to some location in thedomain name space.PTR records cause no additional section processing. These RRs are usedin special domains to point to some other location in the domain space.These records are simple data, and dont imply any special processingsimilar to that performed by CNAME, which identifies aliases. See thedescription of the IN-ADDR.ARPA domain for an example. 115. 1153.3.13. SOA RDATA format +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / MNAME / / / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / RNAME / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |SERIAL | | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |REFRESH| | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | RETRY | | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |EXPIRE | | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |MINIMUM| | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 116. 1163.3.13. SOA RDATA format MNAME RFC 2181 Clarications to the DNS Specication "7.3. The SOA.MNAME eld" SOAMNAME 117. 1173.3.13. SOA RDATA format RNAME "@""." "foo@example.com""foo.example.com" SERIAL 32sequence space arithmetic RFC 1982 Serial Number Arithmetic 118. 1183.3.13. SOA RDATA format REFRESH 32 RETRY 32 EXPIRE 32 119. 1193.3.13. SOA RDATA format MINIMUM RRTTL32 RFC 2308 Negative Caching of DNS Queries (DNS NCACHE)TTL 120. 1203.3.14. TXT RDATA format+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+/ TXT-DATA/+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+where:TXT-DATAOne or more s.TXT RRs are used to hold descriptive text. The semantics of the textdepends on the domain where it is found. 121. 1213.4. Internet specic RRs3.4.1. A RDATA format+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+|ADDRESS|+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+where:ADDRESS A 32 bit Internet address.Hosts that have multiple Internet addresses will have multiple Arecords.A records cause no additional section processing. The RDATA section ofan A line in a master file is an Internet address expressed as fourdecimal numbers separated by dots without any imbedded spaces (e.g.,"10.2.0.52" or "192.0.5.6"). 122. 1223.5. IN-ADDR.ARPA domain IN-ADDR.ARPAIP 123. 1233.6. Dening new types, classes, and special namespaces 124. 1244. MESSAGES4. 4.1. Format 4.2. Transport 125. 125 4 example.jp.IN SOA ns.exampele.jp. .. example.jp.IN NS ns.example.jp. com jp ns.example.jp. IN A192.0.2.1 exampleexample co ns www 126. 1264.1. Format4.1. +---------------------+ |Header | +---------------------+ | Question| the question for the name server +---------------------+ |Answer | RRs answering the question +---------------------+ |Authority| RRs pointing toward an authority +---------------------+ |Additional | RRs holding additional information +---------------------+ 127. 1274.1.1. Header section format4.1.1. Header1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA|Z| RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QDCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |ANCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |NSCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |ARCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 128. 1284.1.1. Header section format4.1.1. Header ID 16 QR Query(0)Response(1)1 OPCODE 4 AA Authoritative Answer 1 question 129. 1294.1.1. Header section format4.1.1. Header TC TrunCation RD Recursion Desired RA Recursion Available Z 0 130. 1304.1.1. Header section format4.1.1. Header RCODE Response code 0: No error condition 1: Format error 2: Server failure 3: Name Error 4: Not Implemented 5: Refused 6-15: Reserved for future use. 131. 1314.1.1. Header section format4.1.1. Header QDCOUNT question16 ANCOUNT answer16 NSCOUNT authority16 ARCOUNT additional16 132. 1324.1.1. Header section format4.1.1. Header1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA|Z| RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QDCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |ANCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |NSCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |ARCOUNT| +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 133. 1334.1.1. Header section format4.1.1. Header$ dig @127.0.0.1 emaillab.jp. NS;; Got answer:;; ->>HEADERHEADERHEADER