Higher level protocols Domain Naming System DNS HTTP 1 Overview What do names do identify objects help locate objects define membership in a group specify a role convey knowledge of a secret Name space defines set of possible names consists of a set of name to value bindings 2 Properties Names versus addresses Location transparent versus location dependent Flat versus hierarchical Global versus local Absolute versus relative By architecture versus by convention Unique versus ambiguous 3 Examples Hosts cheltenham cs princeton edu 192 12 69 17 192 12 69 17 80 23 A8 33 5B 9F Files usr llp tmp foo server fileid Users Larry Peterson llp cs princeton edu 4 Examples cont Mailboxes 2 cs princeton edu Name server User 1 user cs princeton edu Mail program 192 12 69 5 192 12 69 5 3 4 TCP 192 12 69 5 5 IP 5 Domain Naming System Hierarchy edu princeton mit cs com gov cisco yahoo nasa nsf mil org arpa navy acm ieee net uk fr ee physics ux01 ux04 Name chinstrap cs princeton edu 6 Name Servers Partition hierarchy into zones edu princeton mit cs ee com gov cisco yahoo nasa nsf mil org net uk fr arpa navy acm ieee physics ux01 ux04 Each zone implemented by two or more name servers Root name server Princeton name server CS name server Cisco name server EE name server 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 NS Value gives domain name for host running name server that knows how to resolve names within specified domain CNAME Value gives canonical name for particle host used to define aliases MX Value gives domain name for host running mail server that accepts messages for specified domain Class allow other entities to define types TTL how long the resource record is valid 8 Root Server princeton edu cit princeton edu NS IN cit princeton edu 128 196 128 233 A IN cisco com thumper cisco com NS IN thumper ciscoe com 128 96 32 20 A IN 9 Princeton Server cs princeton edu optima cs princeton edu NS IN optima cs princeton edu 192 12 69 5 A IN ee princeton edu helios ee princeton edu NS IN helios ee princeton edu 128 196 28 166 A IN jupiter physics princeton edu 128 196 4 1 A IN saturn physics princeton edu 128 196 4 2 A IN mars physics princeton edu 128 196 4 3 A IN venus physics princeton edu 128 196 4 4 A IN 10 CS Server cs princeton edu optima cs princeton edu MX IN cheltenham cs princeton edu 192 12 69 60 A IN che cs princeton edu cheltenham cs princeton edu CNAME IN optima cs princeton edu 192 12 69 5 A IN opt cs princeton edu optima cs princeton edu CNAME IN baskerville cs princeton edu 192 12 69 35 A IN bas cs princeton edu baskerville cs princeton edu CNAME IN 11 Name Resolution Strategies forward iterative recursive Client a cic 1 cicada cs princeton edu 192 12 69 60 8 Local name server Local server need to know root at only one place not each host site wide cache c da s nc pri u ed 1 n eto 2 e 2 du 3 23 8 2 6 1 3 9 8 1 Root name server n eto c 4 n pri cicada cs princeton edu Princeton name server cs princeton edu 192 12 69 5 5 cic a da cic c s a pr 19 da inc 2 1 c s eto 2 6 pr n e 6 9 6 inc du 0 e to n e du 7 CS name server 12 1 2 3 4 5 6 The user clicks on a link to indicate which document is to be retrieved The browser must determine the address that contains the document It does this by sending a query to its local name server Once the address is known the browser establishes a connection to the specified machine usually a TCP connection In order for the connection to be successful the specified machine must be ready to accept TCP connections The browser runs a client version of HTTP which issues a request specifying both the name of the document and the possible document formats it can handle The machine that contains the requested document runs a server version of HTTP It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format The TCP connection is then closed and the user may view the document Web Transfers Revisited 13 Request HTTP client HTTP server Response 14 HTTP Client Server Interaction HTTP server HTTP client Ephemeral Port 80 Port GET 80 TCP TCP 80 STATUS 15 HTTP Request Operations OPTIONS Request information about available options GET Retrieve document in URL HEAD Retrieve metainformation about document in URL POST give information to server PUT store document under specified URL DELETE delete specified URL TRACE loopback request message 16 HTTP Result codes Code 1xx 2xx 3xx 4xx 5xx Type Example Reasons Informational request received Success action successfully received accepted Redirection Page moved further action necessary Client error bad syntax Server error server failed for valid req 17 Application A Application B Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Communication Network Transport Layer Network Layer Network Layer Network Layer Network Layer Data Link Layer Data Link Layer Data Link Layer Data Link Layer Physical Layer Physical Layer Physical Layer Physical Layer Electrical and or Optical Signals Layered Architecture Revisited 18 User Interface Server PI Server DTP Server FTP Control Connection Data User PI User DTP Connection User FTP PI Protocol interpreter DTP Data transfer process FTP Protocol 19 PING C WINDOWS ping nal toronto edu Pinging nal toronto edu 128 100 244 3 with 32 bytes of data Reply Reply Reply Reply from from from from 128 100 244 3 128 100 244 3 128 100 244 3 128 100 244 3 bytes 32 bytes 32 bytes 32 bytes 32 time 118ms time 118ms time 118ms time 118ms TTL 243 TTL 243 TTL 243 TTL 243 C WINDOWS 20