css432: applications 1 css432 domain name system textbook 9.3.1 instructor: joe mccarthy (based on...
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CSS432: Applications 1
CSS432 Domain Name SystemTextbook 9.3.1
Instructor: Joe McCarthy(based on Prof. Fukuda’s slides)
CSS432: Applications 2
Name ServiceDNS
Basic concepts:Name space: set of possible names
identifiers
Bindings: association of names with values E.g., programming language variable bindings
Resolution: provides the value(s) of a name
Name ServerName• Variable length and mnemonic• Location independent
Value• System-provided fixed value• Location dependent
CSS432: Applications 3
Name Service
Hostscheltenham.cs.princeton.edu 192.12.69.17
192.12.69.17 80:23:A8:33:5B:9F Files
/usr/llp/tmp/foo (server, inode)
Users Larry Peterson [email protected]
(UID + host IP)
Name ServerName• Variable length and mnemonic• Location independent
Value• System-provided fixed value• Location dependent
DNS
CSS432: Applications 4
Unix system calls struct hostent h = gethostbyname( const char *hostname ); *(struct in_addr *)*h->h_addr_list; // returns IP list
DNS
Name Service
CSS432: Applications 5
Hierarchy
Nameuw1-320-00.bothell.washington.edu
(Currently, uw1-320-00.uwb.edu)
edu com
washington … mit
ucs
uw1-320-00 medusa
bothell
cisco … yahoo nasa … nsf arpa … navy acm … ieee
gov mil org net uk fr
homer goodall
DNS
Domain Name System
CSS432: Applications 6
Name Servers Partition hierarchy into zones
Rootname server
washingtonname server
Cisconame server
bothellname server
csname server
…
…
Each zone implemented by two or more name servers
edu com
washington … mit
ucs
uw1-320-00 medusa
bothell
cisco … yahoo nasa … nsf arpa … navy acm … ieee
gov mil org net uk fr
homer goodall
administrativeunit
DNS
CSS432: Applications 7
Resource Records Each name server maintains a collection of resource
records
(Name, Value, Type, Class, TTL)
Name/Value: not necessarily host names to IP addresses Type
A: Value is an IP address NS: Value is the corresponding Name Server’s name CNAME: Value is a Canonical NAME (alias) MX: Value is the domain name of this host’s Mail eXchange
server
Class: IN (Internet class) TTL: how long the resource record is valid
DNS
CSS432: Applications 8
Name Resolution Client
Initialized with its local name server’s address
appends its domain name (e.g., cs.princeton.edu) to a given host name (e.g., penguins)before a submission
Local name server needs to know root at only one place
(not each host). caches recent responses from
remote servers.
DNS
CSS432: Applications 9
dig @server name type Find a root name server
dig edu ns edu a.gtld-server.net NS IN a.gtld-server.net 192.5.6.30 A IN
Find uwb.edu’s name servers dig @192.5.6.30 uwb.edu ns
uwb.edu, dns2.uwb.edu NS IN uwb.edu, dns4.uwb.edu NS IN dns2.uwb.edu 69.91.206.28 A dns4.uwb.edu 69.91.206.29 A
Find mercury.uwb.edu dig @69.91.206.28 metis.uwb.edu A
metis.uwb.edu 69.91.206.17 A
DNS
Name Resolution via dig