Domain Names Implementation and specification

陳怡良　 cyl@mail.im.tku.edu.tw

RFC #1035

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Overview

Provide a mechanism for naming resources User’s view Resolver’s view Two kinds of data:

Authoritative Cache

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Common configuration

User

Program

Local host

User queries

User responses

Resolver

cache

responses

queries

cache additions reference

Foreign

Foreign

Name

Server

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Common configuration(cont.)

Master

files

Local host

Name

Server

Foreign

Resolver

Foreign

Name

Server

Foreign

maintenance responses

queriesmaintenance queries

responses

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Conventions

Preferred name syntax <domain> ::= <subdomain> | “ “ <subdomain> ::= <subdomain> “.” <label> <label> ::= <letter> [[ <ldh-str> ] <let-dig> ] <ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str> <let-dig-hyp> ::= <let-dig> | “=“ <let-dig> ::= <letter> | <digit> <letter> ::= [A-Z][a-z] <digit> ::= [0-9]PS.Labels must be 63 characters or less.

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Conventions(cont.)

Data Transmission Order--octets

Character Case—case-insensitive

Size limits labels 63 octets or less names 255 octets or less TTL positive values of a signed 32 bit number UDP messages 512 octets or less

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RR definitions--Format

NAME

TYPE

CLASS

TTL

RDLENGTH

RDATA

1111110123456789012345

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RR definitions(cont.)--TYPE values

TYPE Value and meaning TYPE Value and meaning

A 1 a host address MR 9 a mail domain name(EXP)

NS 2 an authoritative name server NULL 10 a null RR(EXP)

MD 3 a mail destination(obsolete) WKS 11 a well know service description

MF 4 a mail forwarder(obsolete) PTR 12 a domain name pointer

CNAME 5 the canonical name for an alias HINFO 13 a host information

SOA 6 marks the start of a zone of

authority

MINFO 14 mailbox or mail list information

MB 7 a mailbox domain name(EXP) MX 15 mail exchange

MG 8 a mail group(EXP) TXT 16 txt strings

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RR definitions(cont.)

QTYPEQTYPE value and meaning

AXFR 252 A request for a transfer of an entire zone

MAILB 253 A request for mailbox-related records(MB, MG or MR)

MAILA 254 A request for mail agent RRs (Obsolete)

* 255 A request for all records

CLASSvalue and meaning

IN 1 the Internet

CS 2 the CSNET class(Obsolete)

CH 3 the CHAOS class

HS 4 Hesiod

QCLASS

value and meaning

* 255 any class

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RR definitions(cont.) –SOA RDATA format

MNAME

RNAME

SERIAL

REFRESH

RETRY

EXPIRE

MINIMUM

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Messages--Format

Header

Question

Answer

Authority

Additional

ID

QR Opcode AA TC RD RA Z Opcode

QDCOUNT

ANCOUNT

NSCOUNT

ARCOUNT

1111110123456789012345

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Messages(cont.)--Format

OPCODE

0 QUERY

1 IQUERY

2 STATUS

3-15 reserved

RCODE

0 No error condition

1 Format error

2 Server failure

3 Name Error

4 Not Implemented

5 Refused

6-15 reserved

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Messages(cont.)—Question section format

1111110123456789012345

QNAME

QTYPE

QCLASS

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Messages(cont.)—Resource record format

The answer, authority, and additional sections 1111110123456789012345

NAME

TYPE

CLASS

TTL

RDLENGTH

RDATA

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Resolver Implementation& Mail support Transforming a user request into a query Sending the queries Processing responses Using the cache

Mail support <local-part>@<mail-domain>

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Master Files相關範例— named.conf節錄

zone "200.13.163.IN-ADDR.ARPA" { type master; file "rev.200";};zone "im.tku.edu.tw" { type master; file "hosts.im"; allow-update { none; };};

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Master Files相關範例 (cont.)—rev.200節錄$TTL 86400;@ IN SOA mail.im.tku.edu.tw. root.mail.im.tku.edu.tw. ( 2000092915 ; Serial 43200 ; Refresh 3600 ; Retry 3600000 ; Expire 2419200 ) ; Minimum

IN NS mail.im.tku.edu.tw. IN NS mis.im.tku.edu.tw. IN NS tkgis.tku.edu.tw.

;IMNA Servers30 IN PTR web.im.tku.edu.tw.32 IN PTR mis.im.tku.edu.tw.33 IN PTR sun.im.tku.edu.tw.37 IN PTR wwwbbs.im.tku.edu.tw.39 IN PTR ftp.im.tku.edu.tw.40 IN PTR bbs.im.tku.edu.tw.222 IN PTR mail.im.tku.edu.tw.

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Master Files相關範例 (cont.)—hosts.im節錄$TTL 86400;@ IN SOA mail.im.tku.edu.tw. root.mail.im.tku.edu.tw. ( 2001092980 ; Serial 10800 ; Refresh 3600 ; Retry 3600000 ; Expire 2419200) ; Time to live

IN NS mail.im.tku.edu.tw. IN NS mis.im.tku.edu.tw. IN MX 1 mail.im.tku.edu.tw. IN MX 2 mis.im.tku.edu.tw.

mail IN A 163.13.200.222mis IN A 163.13.200.32sun IN A 163.13.200.33www IN CNAME sunwwwbbs IN A 163.13.200.37

IN MX 0 wwwbbs.im.tku.edu.tw.bbs IN A 163.13.200.40