Name and Address Conversions

1
Name and Address Conversions

• Chap 11

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
Domain, Delegation, Zone
5
Name Server Architecture
From disk
Zone transfer
6
Authoritative Data
Response
Query
7
Using Other Name Servers
Response
Response
Query
Query
8
Cached Data
Response
Query
9
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

10
Mapping Addresses to Names
11
Resource Records

• ?? RRs
• SOA Record (Start Of Authority) ?? ???? ?? ?????
  ??(authoritative)? ??? ?? ??? ??
• NS(Name Server) Record ?? ???? ?? delegation??
  ????? ??
• A Record ???? IPv4 ??? mapping
• AAAA Record ???? IPv6 ??? mapping
• CNAME Record ???? ?? ? ?? ?? ??
• MX(Mail eXchanger) Record ?? ???? ?? ??? ??? ??
• PTR(Pointer) Record IP ??? domain name?? reverse
  mapping? ??, Reverse Zone ???? ??

NAME (Dynamic)
TYPE(2 Byte)
CLASS(2 Byte)
TTL(4 Byte)
RDLENGTH(2 Byte)
RDATA(Dynamic)
12
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)
13
Service Name Conversion Functions

• Service name ? port ( See /etc/services )
• Port ? service name

14
Example name/daytimetcpcli1.c
Network-related information
15
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)

16
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

17
getaddrinfo Actions and Results
18
UNP 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 error
• saptr 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

19
tcp_connect and tcp_listen Functions
20
Protocol-indep Daytime TCP Client/Server
names/daytimetcpsrv1.c
names/daytimetcpcli.c
21
Protocol-indep Daytime UDP Client/Server
names/daytimeudpcli1.c
names/daytimeudpsrv2.c
22
getnameinfo Function

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