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Name and Address Conversions

Name and Address Conversions. Domain 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

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Name and Address Conversions

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  1. Name and Address Conversions

  2. Domain 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

  3. Domain 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.

  4. Header Question : the question for the name server Answer : RRs answering the question Authority : RRs pointing toward an authority Additional : RRs holding additional information Name 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

  5. Mapping Addresses to Names

  6. 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 delegation하는 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 name으로 reverse mapping해 주며, Reverse Zone 파일에서 사용 Resource Records

  7. Name 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); • }

  8. Service Name Conversion Functions • Service name  port ( See /etc/services ) • Port  service name

  9. Example: name/daytimetcpcli1.c Network-related information

  10. 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) Protocol Independent Name/Address Conversion (1)

  11. Protocol Independent Name/Address Conversion (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

  12. getaddrinfo Actions and Results

  13. If the caller does not want to return host(serv) string, specify hostlen(servlen) of 0 flags getnameinfo Function

  14. Protocol Independent Functions

  15. Protocol-indep Daytime TCP Client/Server names/daytimetcpcli.c names/daytimetcpsrv1.c

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