Internet: Names and AddressesAnnouncementsNaming in the InternetLocating the resourcesLocating the Hosts?Mapping Not 1 to 1How to get a name?Domain name structureTop-level Domains (TLDs)How to get a domain name?How to get an IP Address?How to get lots of IP Addresses? Internet RegistriesAre there enough addresses?DHCP and NATsNATs in operationDNS: Domain Name SystemDNS name serversName Server Zone StructureName Servers (NS)Slide 20DNS: Root name serversSimple DNS exampleDNS exampleDNS ArchitectureDNS: query resolutionDNS records: More than Name to IP AddressnslookupPTR RecordsArpa top level domainWhy is it backwards?In-addr.arpa domainDNS protocol, messagesSlide 33Summary1Internet: Names and Addresses2Announcements•Usual announcements–Project 4 is due today Monday, April 9th–Homework 5 available later today, due next Wednesday, April 11th–Prelim II will be Thursday, April 26th, 7:30-9:00pm, in PH 101•Einar Vollset will teach Wednesday, Friday, and Monday (April 11th, 13th, and 16th, respectively)–He will have office hours 4-5pm in Room Upson 4114–Also, Joy will have an extra office hour on Wednesday 3-4pm3Naming in the Internet•What are named? All Internet Resources.–Objects: www.cs.cornell.edu/courses/cs414/2007sp–Services: weather.yahoo.com/forecast–Hosts: planetlab1.cs.cornell.edu•Characteristics of Internet Names–human recognizable–unique–persistent•Universal Resource Names (URNs)4Locating the resources•Internet services and resources are provided by end-hosts–ex. web2.cs.cornell.edu hosts cs414’s home page.•Names are mapped to Locations–Universal Resource Locators (URL)–Embedded in the name itself: ex. weather.yahoo.com/forecast•Semantics of Internet naminghuman recognizableuniquenessxpersistent5Locating the Hosts?•Internet Protocol Addresses (IP Addresses)–ex. planetlab1.cs.cornell.edu 128.84.154.49•Characteristics of IP Addresses–32 bit fixed-length–enables network routers to efficiently handle packets in the Internet•Locating services on hosts–port numbers (16 bit unsigned integer) 65536 ports–standard ports: HTTP 80, FTP 20, SSH 22, Telnet 206Mapping Not 1 to 1•One host may map to more than one name –One server machine may be the web server (www.foo.com), mail server (mail.foo.com)etc. •One host may have more than one IP address–IP addresses are per network interface•But IP addresses are generally unique!–two globally visible machines should not have the same IP address–Anycast is an Exception:•routers send packets dynamically to the closest host matching an anycast address7How to get a name?•Naming in Internet is Hierarchical–decreases centralization–improves name space management•First, get a domain name then you are free to assign sub names in that domain–How to get a domain name coming up•Example: weather.yahoo.com belongs to yahoo.com which belongs to .com–regulated by global non-profit bodies8Domain name structureccTLDsroot (unnamed)com milgovedu grorgnet fr ukus......cornell ustreassecond level (sub-)domainslucentgTLDsgTLDs= Generic Top Level Domains ccTLDs = Country Code Top Level Domains9Top-level Domains (TLDs)•Generic Top Level Domains (gTLDs)–.com - commercial organizations–.org - not-for-profit organizations–.edu - educational organizations–.mil - military organizations–.gov - governmental organizations–.net - network service providers–New: .biz, .info, .name, …•Country code Top Level Domains (ccTLDs)–One for each country10How to get a domain name?•In 1998, non-profit corporation, Internet Corporation for Assigned Names and Numbers (ICANN), was formed to assume responsibility from the US Government•ICANN authorizes other companies to register domains in com, org and net and new gTLDs–Network Solutions is largest–(In transitional period between US Govt and ICANN had sole authority to register domains in com, org and net)11How to get an IP Address?•Answer 1: Normally, answer is get an IP address from your upstream provider–This is essential to maintain efficient routing!•Answer 2: If you need lots of IP addresses then you can acquire your own block of them.–IP address space is a scarce resource - must prove you have fully utilized a small block before can ask for a larger one and pay $$ (Jan 2002 - $2250/year for /20 and $18000/year for a /14)12How to get lots of IP Addresses? Internet RegistriesRIPE NCC (Riseaux IP Europiens Network Coordination Centre) for Europe, Middle-East, AfricaAPNIC (Asia Pacific Network Information Centre )for Asia and PacificARIN (American Registry for Internet Numbers) for the Americas, the Caribbean, sub-saharan AfricaNote: Once again regional distribution is important for efficient routing!Can also get Autonomous System Numnbers (ASNs from these registries13Are there enough addresses?•Unfortunately No!–32 bits 4 billion unique addresses–but addresses are assigned in chunks–ex. cornell has four chunks of /16 addressed•ex. 128.84.0.0 to 128.84.255.255•128.253.0.0, 128.84.0.0, 132.236.0.0, and 140.251.0.0•Expanding the address space!–IPv6 128 bit addresses–difficult to deploy (requires cooperation and changes to the core of the Internet)14DHCP and NATs•Dynamic Host Control Protocol–lease IP addresses for short time intervals–hosts may refresh addresses periodicallyonly live hosts need valid IP addresses•Network Address Translators–Hide local IP addresses from rest of the world–only a small number of IP addresses are visible outsidesolves address shortage for all practical purposesaccess is highly restricted•ex. peer-to-peer communication is difficult15NATs in operation•Translate addresses when packets traverse through NATs•Use port numbers to increase number of supportable flows16DNS: Domain Name SystemDomain Name System:•distributed database implemented in hierarchy of many name servers•application-layer protocol host, routers, name servers communicate to resolve names (address/name translation)–note: core Internet function implemented as application-layer protocol–complexity at network’s “edge”17DNS name serversName server: process running on a host that processes DNS requestslocal name servers:–each ISP, company has local (default) name server–host DNS query first goes to local name serverauthoritative name server:–can perform name/address translation for a specific domain or zone How could we provide this service? Why
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