Transcript ppt
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 [email protected] 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 arpa … navy acm … ieee net uk fr 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 Root name server 2 – forward – iterative – recursive 3 1 cicada.cs.princeton.edu Client 192.12.69.60 8 4 Local name server cicada.cs.princeton.edu Princeton name server cs.princeton.edu, 192.12.69.5 5 • Local server – need to know root at only one place (not each host) – site-wide cache 6 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 Control Server PI Server DTP Server FTP 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