Name and Address ConversionsName and Address Conversions

Chap 11

Domain Name SystemDomain Name System

A lookup mechanism for translating objects into other objects

A globally distributed, loosely coherent, scalable, reliable, dynamic database

Comprised of three components Name space Servers making that name space available Resolvers (clients) which query the servers about the

name space

Domain Name SpaceDomain Name Space

DNS's distributed database is indexed by domain names. Each domain name is essentially just a path in a large

inverted tree, called the domain name space.

Domain, Delegation, Zone Domain, Delegation, Zone

Name Server ArchitectureName Server Architecture

Master

serverZone transfer

Zone

data

file

From

diskAuthoritative Data

(primary master and

slave zones)

Agent

(looks up queries

on behalf of resolvers)

Cache Data

(responses from

other name servers)

Name Server Process

Authoritative DataAuthoritative Data

ResolverQuery

Response

Authoritative Data

(primary master and

slave zones)

Agent

(looks up queries

on behalf of resolvers)

Cache Data

(responses from

other name servers)

Name Server Process

Using Other Name ServersUsing Other Name Servers

Arbitrary

name

server

Response

ResolverQuery

Query

Authoritative Data

(primary master and

slave zones)

Agent

(looks up queries

on behalf of resolvers)

Cache Data

(responses from

other name servers)

Name Server Process

Response

Cached DataCached Data

Query

Response

Authoritative Data

(primary master and

slave zones)

Agent

(looks up queries

on behalf of resolvers)

Cache Data

(responses from

other name servers)

Name Server Process

Resolver

Name ResolutionName Resolution

A DNS query has three parameters: A domain name (e.g.,

ice.hufs.ac.kr), Remember, every node

has a domain name! A class (e.g., IN), and A type (e.g., A)

DNS message format

AdditionalAuthorityAnswerQuestionHeader

: the question for the name server : RRs answering the question : RRs pointing toward an authority : RRs holding additional information

Mapping Addresses to NamesMapping Addresses to Names

Resource RecordsResource Records 주요 RRs

SOA Record (Start Of Authority): 해당 도메인에 대해 네임서버가 인증 (authoritative) 된 자료를 갖고 있음을 의미

NS(Name Server) Record: 해당 도메인에 대한 delegation 하는 네임서버를 지시

A Record: 도메인에 IPv4 주소를 mapping AAAA Record: 도메인에 IPv6 주소를 mapping CNAME Record: 도메인에 대한 또 다른 이름

설정 MX(Mail eXchanger) Record: 해당 호스트의

메일 라우팅 경로를 조정 PTR(Pointer) Record: IP 주소를 domain name

으로 reverse mapping 해 주며 , Reverse Zone 파일에서 사용

NAME

(Dynamic)

TYPE(2 Byte)

CLASS(2 Byte)

TTL(4 Byte)

RDLENGTH(2 Byte)

RDATA(Dynamic)

Name and Address Conversion FunctionsName and Address Conversion Functions

Domain name IPv4 address

IPv4 address domain name

gethostbyname/gethostbyaddr are not reentrant !!static struct hostent host; /* result stored here */struct hostent *gethostbyname(const char *hostname){ /* call DNS functions for A or AAAA query */ /* fill in host structure */ return(&host);}

Service Name Conversion FunctionsService Name Conversion Functions

Service name port ( See /etc/services )

Port service name

Example: name/daytimetcpcli1.cExample: name/daytimetcpcli1.c

Network-related information

New Name/Address Conversion Function (1)New Name/Address Conversion Function (1)

hostname: hostname or address string service: service name or decimal port

number string result: addrinfo data structure is

dynamically allocated Re-entrant, thread-safe, and protocol

independent functions (support IPv4, IPv6)

New Name/Address Conversion Function (2)New Name/Address Conversion Function (2)

hints: NULL or pointer to addrinfo data structure The following member can be set by caller

ai_flag /* AI_PASSIVE for server, AI_CANNONNAME */ ai_family /* AF_xxx */ ai_socktype /* SOCK_xxx */ ai_protocol /* 0 or IPPROTO_xxx for IPv4 and IPv6 */

Example

getaddrinfogetaddrinfo Actions and Results Actions and Results

UNP Library FunctionsUNP Library Functions#include “unp.h”

struct addrinfo *host_serv(const char *hostname, const char *service, int family, int socktype);

Returns: pointer to addrinfo structure if OK, NULL on error

int tcp_connect(const char *hostname, const char *service);int tcp_listen(const char *hostname, const char *service,

socklen_t *lenptr);Both returns: connected socket descriptor if OK, no return on error

int udp_client(const char *hostname, const char *service, void **saptr, socklen_t *lenp);

Returns: unconnected socket descriptor if OK, no return on errorsaptr: address of a pointer to a socket address structure that stores destination IP addr/port # for future calls to sendto

int udp_connect(const char *hostname, const char *service);Returns: connected socket descriptor if OK, no return on error

int udp_server(const char *hostname, const char *service, socklen_t *lenptr);

Rerurns: unconnected socket descriptor if OK, no return on error

tcp_connecttcp_connect and and tcp_listentcp_listen Functions Functions

Protocol-indep Daytime TCP Client/ServerProtocol-indep Daytime TCP Client/Servernames/daytimetcpsrv1.c names/daytimetcpcli.c

Protocol-indep Daytime UDP Client/ServerProtocol-indep Daytime UDP Client/Server

names/daytimeudpsrv2.c names/daytimeudpcli1.c

getnameinfogetnameinfo Function Function

If the caller does not want to return host(serv) string, specify hostlen(servlen) of 0

flags