CMPE 150 Introduction to Computer Networks Dr Chane L Fullmer chane cse ucsc edu Spring 2003 UCSC cmpe150 1 Homework Assignments Homework assignment 4 Chapter three Due May 29 TODAY Spring 2003 UCSC cmpe150 2 Homework Assignments Homework assignment 5 Chapter two Due June 5th only one short week from today Spring 2003 UCSC cmpe150 3 Optional Class Project Network programming project Goal In lieu of taking final examination Or just a wildcard for mid term or final Build an FTP client server from scratch Using C language Details on web page now Due by next Wednesday Spring 2003 UCSC June 4th cmpe150 4 Class Final Exam Final exam Three hours 40 50 questions comprehensive Multiple choice as the midterm Scantron bring your sheet and pencils Wednesday June 11th 8 00 11 00am Thirteen days Tick tick tick Spring 2003 UCSC cmpe150 5 CMPE 150 Introduction to Computer Networks Set 16 Application level Protocols Spring 2003 UCSC cmpe150 6 Applications Name directory services DNS Remote terminal access Telnet File transfer FTP Web access http Electronic mail SMTP Internet telephony and streaming Spring 2003 UCSC cmpe150 7 Applications and application layer protocols Application communicating distributed processes e g e mail Web P2P file sharing instant messaging running in end systems hosts exchange messages to implement application application transport network data link physical Application layer protocols one piece of an app define messages exchanged by apps and actions taken use communication services provided by lower layer protocols TCP UDP Spring 2003 UCSC application transport network data link physical cmpe150 application transport network data link physical 8 Processes communicating across network process sends receives messages to from its socket socket analogous to door sending process shoves message out door sending process assumes transport infrastructure on other side of door which brings message to socket at receiving process Spring 2003 UCSC host or server host or server controlled by app developer process process socket socket TCP with buffers variables Internet TCP with buffers variables controlled by OS cmpe150 9 DNS Hierarchical name space Distributed database RFCs 1034 and 1035 Spring 2003 UCSC cmpe150 10 Domain Name System DNS Basic function translation of names ASCII strings to network IP addresses and viceversa Example zephyr isi edu 128 9 160 160 Try the nslookup program even in Windoze nslookup zephyr isi edu or any other name you whish to resolve Spring 2003 UCSC cmpe150 11 DNS Domain Name System People many identifiers SSN name passport Domain Name System Internet hosts routers IP address 32 bit used for addressing datagrams name e g gaia cs umass edu used by humans Q map between IP addresses and name Spring 2003 UCSC distributed database implemented in hierarchy of many name servers application layer protocol host routers name servers to communicate to resolve names address name translation note core Internet function implemented as applicationlayer protocol complexity at network s edge cmpe150 12 History Original approach ARPANET 1970 s File hosts txt listed all hosts and their IP addresses Every night every host fetches file from central repository OK for a few hundred hosts Scalability File size Centrally managed Spring 2003 UCSC cmpe150 13 How is it used Client server model Client DNS running on client hosts or resolver Application calls resolver with name Resolver contacts local DNS server using UDP passing the name Server returns corresponding IP address Spring 2003 UCSC cmpe150 14 DNS Name Space A Tree based Hierarchy int ibm com edu Spring 2003 org net us ca ucsc cse eng sales gov mil cats soe UCSC cmpe150 15 Name Space Structure Top level domains Generic Countries In practice all US organizations are under a generic domain while everything outside the US is under the corresponding country domain Spring 2003 UCSC cmpe150 16 DNS Names Domain names Concatenation of all domain names starting from its own all the way to the root separated by a dot Reverse order of IP addresses Refers to a tree node and all names under it Case insensitive Components up to 63 characters Full name less than 255 characters Spring 2003 UCSC cmpe150 17 Name Space Management Domains are autonomous Organizational boundaries Each domain manages its own name space independently of other domains Delegation When creating new domain register with parent domain Spring 2003 For name uniqueness For name resolution UCSC cmpe150 18 Resource Records Entry in the DNS database Several types of entries or RRs Example RR A contains IP address RR format five tuple Name TTL in seconds Class usually IN for Internet info Type type of RR Value Spring 2003 UCSC cmpe150 19 RR Types SOA start of authority A address Marks beginning of zone s database Provides general info about the zone e mail address of admin default TTL etc Contains 32 bit IP address Single name several A RRs MX mail exchange Name of mail server for this domain Spring 2003 UCSC cmpe150 20 RR Types NS name server CNAME canonical name Alias HINFO host description Name of name server for this domain Provides information about host e g CPU type OS etc TXT arbitrary string of characters Generic description of the domain where it is located etc Spring 2003 UCSC cmpe150 21 Name Servers Entire database in a single name server DNS database is partitioned into zones Each zone contains part of the DNS tree Zone name server Practical Why Each zone may be served by more than one server A server may serve multiple zones Primary and secondary name servers Spring 2003 UCSC cmpe150 22 DNS Root name servers Contacted by local name server that cannot resolve name Root name server contacts authoritative name server if name mapping not known gets mapping returns mapping to local name server a NSI Herndon VA c PSInet Herndon VA d U Maryland College Park MD g DISA Vienna VA h ARL Aberdeen MD j NSI TBD Herndon VA k RIPE London i NORDUnet Stockholm m WIDE Tokyo e NASA Mt View CA f Internet Software C Palo Alto CA 13 root name servers worldwide b USC ISI Marina del Rey CA l ICANN Marina del Rey CA Spring 2003 UCSC cmpe150 23 Name Resolution Application wants to resolve name Resolver sends query to local name server Resolver configured with list of local name servers Select servers in round robin fashion If name is local local name server returns matching authoritative RRs Authoritative RR comes from authority managing the RR and is always correct Cached RRs may
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