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by: Amira Cormier

ComputerNetworks CS4590

Amira Cormier

GPA 3.55


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Class Notes
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This 0 page Class Notes was uploaded by Amira Cormier on Monday November 2, 2015. The Class Notes belongs to CS4590 at California State University - East Bay taught by Staff in Fall. Since its upload, it has received 10 views. For similar materials see /class/234375/cs4590-california-state-university-east-bay in ComputerScienence at California State University - East Bay.


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Date Created: 11/02/15
Naming Domain Naming System Distributed File Systems Network Applications Include network protocols which allow messages to be exchanged between peer processes Domain Names system is one ofthe rst applications implemented on a network Works behind the scenes Middleware Overview What do names do 7 identify objects 7 help ocate objects 7 define membership in a group 7 specify are e Name space 7 defines set ofpossible names 7 consists ofa set ofname to value bmdmgs A Naming System Need a name space 7 hierarchical or at a collection ofbindings ofnames to values 7 IP addresses or other info A resolution mechanism is needed to look up the names name server is an implementation ofa resolution mechanism that can be queried Properties of Names Names versus addresses Location transparent versus locationdependent Flat versus hierarchical Global versus local Absolute versus relative By architecture versus by convention Unique versus ambiguous Examples osts cheltenhamcs pzincetonedu7gt 192 126917 192 12 69 17 39 an 23 na 33 559r Files us11ptmpfoo server fileid sers Larry retezsona 11p cs pzinceton edu History I In the ARPANet the Network Information Center N IC centrally controlled and maintained a single HOSTSTXT le with nameIP mappings and every day the le was FTPed by all hosw to stay current I Impossible today 7 Need it to be maintained in a distributed manner with local caching to improve performance History A convention for naming was created so that two organizations did not decide to use the same host name for their computers Internet Corporation or Assigned Names and Numbers ICANN has controled this since 1999 previously Network Solutions had exclusive rights to assigning names Five other companies have been given these rights since These include CORE Network Solutions Melbourne IT Oleane FR telecom and registercom DNS I The Domain Name System is de ned in RFCs 1034 and 1035 I Create a network of servers called Domain Name I These servers maintain a distributed database of mappings from host names to IP addresses Servers only need to maintain mappings which are local to their region I Name servers are then organized hierarchically Domain Naming System I Hierarchy h A A A A A A A I Name p eesaeess rraise ea ism Name Servers I Partition hierarchy into zones I Each zone implemented by two or more name servers I 13 root servers store all top level domain names Root Servers I As of2000 the root name servers are operated by the US military commercial organizations non pro t organizations Internet service providers universities and research institu es I 3 ofthe 13 servers being operated outside the US one in London administered from the Netherlands one in Japan and one in Sweden I See Processing From the root directory you go to sub domain directories to ndthe individual organization s domain second tier and on down Eventually you get to the default local domain server for your area which could be on your particular network or farther away Most enterprises have one Erimg name server and several secondary servers 7 Decrease latency e lmprovereliablility Implementation I The user programs access name servers through standard programs called resolvers I The resolver sends a message UDP or TCP to the local Domain ame Server I The DNS server looks up the mapping and returns the result to the resolver I On the Suns you can look to see Which domain nam servers are queried by looking at etdresolvconf I On most systems the DNS location service software is in a suite called BIND Berekely Internet Name Domain Re source Records Each name server maintains a collection ofremurce retunlx minimums mine rm rm DomainiName 7 domain name Value 7 anumber domain name or ASCH string depending on the record type Type 7 type ofrecord 7 NS Value gives domain name for host running name serverthat knows how to resolve names within speclfled doma n e CNAME Value gives canonical name forpartlcle host used to deflne aliases e MX Value gives domain name for host running mail sewer that accepts messages for specified domain Resource Records I Each name server maintains a collection of rmnurcz records Domain ame Value Type Class TTL I Class allows other entities to de ne useful records types IN is the one most Widely used I TTL how long the resource record is valid cached pages will have lower numbers than original pages Root Server pincetonedu citpincetonedu us In citpincetonedu 125196125233 5 1n ciscocom thumpeciscocom l4 thulnpeciscoecom 125963220 5 1n Princeton Server own records some ofwhlch contain the nal answer and some ofwhlch pointto third level name servers cspincetonedu optimacspzincetonedu us In 39 39 2 A II optuna cs pnnceton edu 1 2695 ee pnncetonedu he1ioseepnnceton ed s In 105 ea prince d 125196 25 6 a 1n jupxte physxcspzxnceton edu 125 196 4 1 a 1n satu ph sxcs princeton 196 4 1n mars physxcs pnnceton edu 5 196 4 3 a III Venusphysicspzincetonedu 12519644 5 1n CS Server Third level Princeton serve contains the A records for all of its hosts it may contain aliases for the hosts cspincetonedu optimacspzincetonedu m m cheltenhamcspzincetonedu 192126960 1 1n lh nrin n in h n nham nrin n d1 n 1n optimacspzincetonedu 19212695 a 1n optcspzincetonedu optimacspzincetonedu me In lh nrin cums 1n baskezvillecspzincetonedu 192126935 3 In n in h krrn39ll nrin n dll Aliases amp Resolving Good ifyou are going to provide an external service web or emaii Can move the service to anothermachine without affecting remote users Many UNIX machines act as their own name server maintaining a small database ofmappings see etchosts The reso1ver process may have its own database and possib1y a 1oc cache ofmappings It will search this rst before contacting an external DNS server from reso1v conf Name Resolution I Strategies 7 i erati r recursive I Local server 7 need to know root at on1y one p1ace not each host 7 sitewide cache Iterative Query I The queried name server passes back the address of the next name server in the chain I The source must then query the next names server etc I Does not require saving state at each names server in e c ain Recursive Query I The name servers might cache the replies in case they are needed again 7 assign a short Tl39L since it is not authoritative I Each query to a name server generates another 7 name servers mnstmaintain some kind ofstate about the query nntii the response comes back Resolving Recursively Resolve salurncsprincelonedu from huzzacsuhaywardedu Ifnot in local host or name server cache it goes right to the top root 1t contacts the toplevel name server for the host edu corn etc The toplevel name servers do not maintain mapping for all the hosts in their domains but they do have mappings for all oftheir own second 1eve1s Resolving I The root server Would contact the princetonEDU server I That server must maintain mappings for all is children including the Saturn machine I It Will return all the resource records that it has regarding the Saturn machine I The information Will propagate back to the resolver process Name Resolution Where is the root server I Local system must have a mapping for one or more root servers 7 published and updated manually I the clienthost is also con gured With the M domain on Which the host resides so it can concatenate this name before contacting the DNS 7 For partial names without the domain e g snazzy on our system New Version I Dynamic DNS RFC 2136 allows the DNS database to updated automatically Without requiring manual updates I Link it to DHCP so that machines Which have been assigned IP addresses dynamically could be addressed via DNS Other naming systems I X500 7 used in DCE and some CORBA implementations I LDAP 7 modi ed from X500 for locating objects across the Internet Naming Tricks I Symbolic links I Mount points I Union mounw I PerUser name spaces I Logical name spaces I Computed directories


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