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Networking Basics

Networking Basics. Gorazd Božič Academic and Research Network of Slovenia gorazd.bozic@arnes.si. Terminology. network set of objects/elements exchanging information protocol describes how information is exchanged. Centralised (“star”) topology.

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Networking Basics

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  1. Networking Basics Gorazd BožičAcademic and Research Network of Sloveniagorazd.bozic@arnes.si

  2. Terminology • network • set of objects/elements exchanging information • protocol • describes how information is exchanged

  3. Centralised (“star”) topology • all communication has to pass through main hub • single point of failure • no redundancy main hub

  4. Distributed (“mesh”) topology • sites can be connected to more than one other site • alternative paths are possible

  5. Packet switching message ... ... ... • chance of error is proportional to length of the message • whole message has to be retransmitted • message is split into smaller units and reassembled at destination • individual packets can take different routes

  6. Routing traffic • how do we know which path to take to get from A to B? • announcing neighbours • estimating cost of each path • building a representationof network on each node A B

  7. Addressing • each network device is assigned an IP address • 32-bits, represented as A.B.C.D • IANA (Internet Assigned Numbers Authority) delegates larger chunks to: • RIPE NCC (Europe, Africa, Middle East) • ARIN (North and South America) • APNIC (Asian-Pacific area) • reserved address space for private networks

  8. Types of network devices Internet • routers: routing (directing) traffic to appropriate destinations • all other devices: computers (desktop, servers), printers, scanners, other specialised hardware

  9. ISO/OSI network model Application layer end-user services (mail/SMTP, web/HTTP, ...) Presentation layer standard canonical forms for data(byte ordering) Session layer Format of data sent over the network Transport layer Transmission Control Protocol (TCP)User Datagram Protocol (UDP) Network layer IP and ICMP; routing between networks, breakingand reassembling packets Data link layer network interface, packet destination, Ethernet Physical layer cable and physical medium, converters between different tyopes if media

  10. Domain name system (DNS) • hierarchical system that provides mapping between IP addresses and readable names • www.arnes.si = 193.2.1.66 (A record) • 66.1.2.193.in-addr.arpa = www.arnes.si (PTR record) • where to send e-mail (MX records) • arnes.si preference = 60, mail exchanger = planja.arnes.si • arnes.si preference = 50, mail exchanger = kanin.arnes.si • where are DNS servers for domain (NS records) • arnes.si nameserver = kanin.arnes.si • arnes.si nameserver = nanos.arnes.si • arnes.si nameserver = niobe.ijs.si

  11. Domain names www.mf.uni-lj.si top-level domain, delegated by IANA to the registry domain registered by an institution (University of Ljubljana),at the registry for the .si top-level domain institution (domain holder) can freely assign space belowtheir second level domain; in this example, each faculty hasa separate namespace (mf = Medical Faculty) local system administrators assign names to individualsystems (computers, printers, ...) under mf.uni-lj.si

  12. Domain name resolution • User: I’d like to know the address of www.mf.uni-lj.si. • Root server: Try kanin.arnes.si, which handles .si top-level domain • I’d like to know the address of www.mf.uni-lj.si. • kanin.arnes.si: Go to ns.uni-lj.si, they handle uni-lj.si domain • I’d like to know the address of www.mf.uni-lj.si. • ns.uni-lj.si: For information on mf.uni-lj.si, go to animus.mf.uni-lj.si • I’d like to know the address of www.mf.uni-lj.si. • animus.mf.uni-lj.si: The address is 193.2.69.12

  13. Models for information exchange • client-server model • dominant model on the internet • clients request information from servers or send information that server will process • peer-to-peer (P2P) networks • all nodes are equal (more or less) • more resiliant to failures • difficult to track information flow • dominantly used for file sharing (KaZaA, eDonkey)

  14. Client-server model • clients can rely on servers to know how to handle information in a request, clients can stay thin (stupid) • servers can accumulate data and log traffic flows • if server fails, service becomes unavailable • examples • DNS (Domain Name System) • SMTP (Simple Mail Transfer Protocol) • HTTP (Hypertext Transfer Protocol)

  15. P2P model • all nodes act as servers and clients • ad-hoc connections between nodes are established as needed • more resiliant to failures • examples nowadays include file sharing P2P networks, can be used also for distributed computing

  16. Distributed computing • problem is split into smaller independent units • these units are hanled separately by different computers • results are combined (sent to the main server) • examples • SETI @ Home • RSA challenge • GRID Computing

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