L5 - Domain Name Systems PDF

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L5 - Domain Name Systems ● Introduced in the 80s ○ IPs matched with Domain Names globally ○ Sometimes top-level domains (TLD) consist of two parts ● Host file - hard to remember IPs ○ Host files to map domain names with IPs ● Resolving domains to IPs - DNS contain info about which IPs belong to which domains ○ Domains resolve to one IP ○ Find IP for a specific domain with a ping ○ Different domains may resolve to the same IP ● Reverse IP lookup - it is possible to lookup which hosts (domains) are sharing one IP ● Top -Level Domains ○ First top-level domains - .com, .net, .org, .edu ○ First domain was symbolics.com ○ Other early adopters - xerox, hp, ibm, sun, intel ○ Top level domains overall are managed by ICANN ○ 1,500+ TLDs managed by 1,000 organisations ● Types of TLDs ○ General TLD - .com, .org ○ Country Code TLD - .ie, .us, .ke ○ Sponsored TLD - .netflix ● Registrars - Thousands of registrars where you can register a domain name, and tens of thousands of resellers ● Creating sub domains ○ Once you own a domain, you can create as many subdomains as you like ○ Subdomains behave like normal domains ○ Emails like [email protected] are possible ● Special subdomains ○ The www in many domains is typically a normal subdomain ○ Sometimes webmasters forget to setup ww and have http only ○ Other common ones are - www1, www2, api, dev, beta, svn ● Subdomain vs directory ○ Subdomains can easily point ot completely different servers or folders ○ Subdomains behave like normal domains, ie. you can set up separate email addresses ○ Managing subdomains is slightly more complex than managing directories ○ Search Engine Optimization ● Importance of good domain names

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○ Domains are comparable to the location of a physical store ○ Domain names may impact the search engine ranking ○ Difficult to remember name might cause people to not be able to return ○ Ambiguous domain name might cause visitors to use competitors site ○ Changing domain name may cause problems Valuable domain name ○ TLD ○ Length ○ Easy to remember ○ Age ○ PageRank ○ Backlinks ○ Search volume Buying and selling domains as a business model - some more expensive than others Ports - a process-specific or an application - specific software construct serving as a communication endpoint ○ Used by Transport Layer Protocols of internet protocol suit ○ Specific network port is identified by its number commonly referred to as port number ○ The IP address in which the port is associated which and the type of the transport protocol used for the communication ○ 16-bit unsigned integer ○ Like doorbells or nameples (IP addresses like street names and addresses) ○ Port in a URL is specified with a : behind the domain Uniform Resource Locator (URL) - address where a resource is located ○ Uniform Resource Name (URN) - name of resource ○ Uniform Resource Identifier (URI) - any of the above ○ URLS similar to a file path on local computer ○ Every application may create a URL handler/scheme and register it in an operating system or browser Protocols and Data Formats ○ Protocol describes handling of data ■ Collection of rules across a network ■ Computers that communicate with each other must use same protocol for data transmission ■ Early computers sued different protocols ■ Each internet application has its own protocol to communicate ■ Comparable to an interface in Java ○ Data format describes structure of data ■ Often a file ■ Typically each internet application has its own data format, some are generic

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■ Each server and client need corresponding software to use/interpret a protocol /data format ○ Computer2Human - needs visualization ○ Computer2Computer - needs meaning ○ Tect - web pages, XML, JSON, Plain text etc ○ Binary - images, videos, sounds, email attachments TCP/IP - Transmission Control Protocol is considered as a reliable protocol ○ Responsible for breaking up the message into TCP segments and reassembling them at the receiving side ○ Not sure that the data reaching at the receiving device is in the same order ○ TCP is responsible for keeping the unordered segments in the right order ○ Assures a reliable delivery by re-sending anything that gets lost while travelling the network ○ Contains the port of the source and destination and checksums OSI model - Open Systems Interconnection Model (OSI model) ○ Defines internetworking in terms of a vertical stack of seven layers ○ Upper layers represent software that implements network services like encryption and connection ○ Lower layers implement more primitive hardware oriented functions like routing and addressing ■ Physical ■ Data link ■ Network ■ Transport ■ Session ■ Presentation ■ Application Echo Protocol - defines how echo is created between client and server ○ client sends messages to server, server returns the same message HTTP - Hypertext Transfer Protocol defines how web clients and web servers communicate ○ Not about the content of a website ○ 2 message types - request and response ○ Most common methods - get, post ○ More methods - options, head, put, delete, connect, trace ○ Code status: ■ 200 Ok ■ 301 Moved Permanently ■ 400 Bad Requests ■ 401 Unauthorized ■ 403 Forbidden ■ 404 Not Found

■ 500 Internal Server Error ● HTTP relevance for e-business ○ Develop websites properly ○ Collect simple statistics about users ○ Know how reliable statistics are ○ Necessary to develop HTTP client or server sometimes ○ Detect potential spammers/crawlers ○ Knowledge necessary for developing web services ○ ‘Reuse’ existing standards for own applications ● Open standards vs proprietary solutions ○ First computers had their own protocols for network communication ○ Dropbox, onedrive, etc have their own protocols, although WebDAV exist for a long time ○ Imagine a website without the HTML standard but proprietary solutions ○ Advantages and disadvantages of standards ■ Less competition - high entry barriers ■ More competition - no USP ■ Competitive advantage for owner of solution ■ Faster development without sticking to standards...