Akademska in raziskovalna mreža Slovenije 1 Networking Basics Gorazd Božič Academic and Research Network of Slovenia

Akademska in raziskovalna mreža Slovenije 2Terminology network –set of objects/elements exchanging information protocol –describes how information is exchanged

Akademska in raziskovalna mreža Slovenije 3 Centralised (“star”) topology all communication has to pass through main hub single point of failure no redundancy main hub

Akademska in raziskovalna mreža Slovenije 4 Distributed (“mesh”) topology sites can be connected to more than one other site alternative paths are possible

Akademska in raziskovalna mreža Slovenije 5 Packet switching 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 message...

Akademska in raziskovalna mreža Slovenije 6 how do we know which path to take to get from A to B? announcing neighbours estimating cost of each path building a representation of network on each node Routing traffic A B

Akademska in raziskovalna mreža Slovenije 7Addressing 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

Akademska in raziskovalna mreža Slovenije 8 Types of network devices routers: routing (directing) traffic to appropriate destinations all other devices: computers (desktop, servers), printers, scanners, other specialised hardware Internet

Akademska in raziskovalna mreža Slovenije 9 ISO/OSI network model Physical layer cable and physical medium, converters between different tyopes if media Network layer IP and ICMP; routing between networks, breaking and reassembling packets Data link layer network interface, packet destination, Ethernet 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)

Akademska in raziskovalna mreža Slovenije 10 Domain name system (DNS) hierarchical system that provides mapping between IP addresses and readable names – = (A record) – in-addr.arpa = (PTR record) where to send (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

Akademska in raziskovalna mreža Slovenije 11 Domain names 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 below their second level domain; in this example, each faculty has a separate namespace (mf = Medical Faculty) local system administrators assign names to individual systems (computers, printers,...) under mf.uni-lj.si

Akademska in raziskovalna mreža Slovenije 12 Domain name resolution 1.User: I’d like to know the address of 2.Root server: Try kanin.arnes.si, which handles.si top- level domain 3.I’d like to know the address of 4.kanin.arnes.si: Go to ns.uni-lj.si, they handle uni-lj.si domain 5.I’d like to know the address of 6.ns.uni-lj.si: For information on mf.uni-lj.si, go to animus.mf.uni-lj.si 7.I’d like to know the address of 8.animus.mf.uni-lj.si: The address is

Akademska in raziskovalna mreža Slovenije 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)

Akademska in raziskovalna mreža Slovenije 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)

Akademska in raziskovalna mreža Slovenije 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

Akademska in raziskovalna mreža Slovenije 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 Home –RSA challenge –GRID Computing