10 DNS HTTP Unix Socket Programming DNS Domain

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10. DNS, HTTP, Unix Socket Programming DNS (Domain Name Service) Domain Name Resolution HTTP

10. DNS, HTTP, Unix Socket Programming DNS (Domain Name Service) Domain Name Resolution HTTP (Hyper Text Transfer Protocol) Request Response Persistent Connection Socket Programming API 1

DNS Overview • Attributes of an object – name – address – itself •

DNS Overview • Attributes of an object – name – address – itself • 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

Properties • • • Names versus addresses Location transparent versus location-dependent Flat versus hierarchical Global versus local Absolute versus relative Unique versus ambiguous 3

Examples • Hosts cheltenham. cs. princeton. edu 192. 12. 69. 17 80: 23: A

Examples • Hosts cheltenham. cs. princeton. edu 192. 12. 69. 17 80: 23: A 8: 33: 5 B: 9 F • 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 @

Examples (cont) • Mailboxes 2 cs. princeton. edu Name server User 1 user @ cs. princeton. edu Mail program 192. 12. 69. 5 3 4 TCP 192. 12. 69. 5 5 IP • Services nearby ps printer with short queue and 2 MB 5

Domain Naming System • Hierarchy • Name chinstrap. cs. princeton. edu 6

Domain Naming System • Hierarchy • Name chinstrap. cs. princeton. edu 6

Name Servers • Partition hierarchy into zones edu princeton … mit cs ee com

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 ux 01 ux 04 • 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,

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.

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.

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.

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 – iterative – recursive Client 1 cicada. cs. princeton. edu

Name Resolution • Strategies – iterative – recursive Client 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 Root 2 name u server. ed n 3 o 3 et 8. 2 nc i 2 r. 1 3. p 96. cs 1 a. ad 28 , 1 cic u d n. e o t e 4 nc i r p cicada. cs. princeton. edu Princeton name server cs. princeton. edu, 192. 12. 69. 5 5 cic ad a. c cic s. p 19 ada rin 2. 1. c ce 2. 6 s. pr ton 9. 6 inc. ed 6 e 0 ton u. ed u, 7 CS name server 12

HTTP • Message format: START_LINE <CRLF> MESSAGE_HEADER <CRLF> MESSAGE_BODY <CRLF> • Request GET http:

HTTP • Message format: START_LINE <CRLF> MESSAGE_HEADER <CRLF> MESSAGE_BODY <CRLF> • Request GET http: //www. cs. princeton. edu/index. html HTTP/1. 0 GET /index. html HTTP/1. 1 Host: www. cs. princeton. edu 13

HTTP Methods in Request – – – – GET: retrieve document HEAD: retrieve meta-information

HTTP Methods in Request – – – – GET: retrieve document HEAD: retrieve meta-information POST: give information to server PUT: store document under specified URL DELETE: delete specified URL TRACE: loopback request message CONNECT: for use by proxies OPTIONS: request information about available options 14

HTTP • Response HTTP/1. 1 404 Not Found HTTP/1. 1 200 OK Server: Netscape-Enterprise/4.

HTTP • Response HTTP/1. 1 404 Not Found HTTP/1. 1 200 OK Server: Netscape-Enterprise/4. 1 Date: … Expires: … CONTENTS of the FILE 15

HTTP • Persistent Connection in HTTP/1. 1 – Image files – Cost of TCP

HTTP • Persistent Connection in HTTP/1. 1 – Image files – Cost of TCP connections – Persistent connection: KEEP-ALIVE 16

Socket Programming API • Server Side (passive open) – – Bind Listen Accept Close

Socket Programming API • Server Side (passive open) – – Bind Listen Accept Close • Client Side (active open) – Bind – Connect – Close 17