Net working So f ar we have t alked pr imar ily about OS 15: Net - - PDF document

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Net working So f ar we have t alked pr imar ily about OS 15: Net working Basics support f or individual comput er syst ems Today we are going t o t alk about net working comput er syst ems t oget her Last Modif ied: 7/ 3/ 2004

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15: Net working Basics

Last Modif ied: 7/ 3/ 2004 1:47:08 PM

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Net working

So f ar we have t alked pr imar ily about OS

support f or individual comput er syst ems

Today we are going t o t alk about

net working comput er syst ems t oget her

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A Net work

A net work is simply a collect ion of nodes,

connect ed by links, t hat communicat e and cooperat e

Nodes = End Host s (PCs, PDAs, t oast er s?),

I nt er nal Nodes (Rout er s, swit ches, hubs,..)

Links = Et her net , Wir eless, point t o point ,…

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Quest ions

What will be t he f or mat of dat a exchanged? How

do we agr ee on a language among all kinds of nodes?

Tr ansmission acr oss links is f ault y can

cor r upt / lose dat a. How can we r eliably exchange inf or mat ion?

How do we f ind t he r ight pat h bet ween t wo nodes?

I f t her e ar e many how do we choose t he best one?

How do nodes r ef er t o one anot her or addr ess one

anot her?

What is t he oper at ing syst ems r ole in all t his?

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Communicat ion?

I f t wo ent it ies are going t o communicat e,

t hey must agree on t he expect ed order and meaning of messages t hey exchange.

Asking f or t he t ime prot ocol

SUCCESSFUL PROTOCOL EXCHANGE

  • Hi …

Hi… Got t he t ime?… .t wo oclock

ABORTED PROTOCOL

  • Hi…

Don’t bot her meXX

PROTOCOL MI SMATCH

  • Allo…

Hello..Quelle heuere a’t il … ..XX< blank st are>

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P rot ocol

Def ines t he f ormat and t he order of

messages exchanged bet ween communicat ing ent it ies

Def ines t he act ions expect ed t o be t aken

  • n t he receipt or t he t ransmission of a

message

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Net working prot ocols

Ok let s def ine t he “language” f or all

int eract ions over t he net work??

One single language t hat can suppor t ever yt hing

f rom web browsing t o email t o f t p t o dist ribut ed f ile syst ems? Human beings are able t o handle lot s of

complexit y in t heir prot ocol processing.

Ambiguously def ined pr ot ocols Many pr ot ocols all at once

How do comput ers manage complex

prot ocol processing?

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Layered Archit ect ures

Br eak-up design problem int o smaller, more

manageable problems

Layers

Design prot ocols t o support each well

def ined t ask

Not one language f or ever yt hing!!

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I nt ernet prot ocol st ack

Application Transport Network Physical users network HTTP, SMTP, FTP, TELNET, DNS, … TCP, UDP. IP Point-to-point links, LANs, radios, ...

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P rot ocol st ack

e-mail client TCP server IP server ethernet driver/card user X SMTP TCP IP e-mail server TCP server IP server ethernet driver/card user Y IEEE 802.3 standard electric signals English

Language Spoken Among Peer s

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P rot ocol encapsulat ion

e-mail client TCP layer IP layer ethernet driver/card user X e-mail server TCP layer IP layer ethernet driver/card user Y “Hello” “Hello” “Hello” “Hello” “Hello”

SMTP Commands TCP Headers I P Headers Et hernet Frame

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P acket Swit ching

Packet s indicat e t heir dest inat ion No predet ermined pat h f or a packet t o

t ake

Each int ermediat e not e rout es t he packet

closer t o it s dest inat ion

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A small I nt ernet

A V R B W r1,e1 r2,e2 r3 a,e3 w,e5 b,e4 Scenario: A wants to send data to B.

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P rot ocol st ack: packet f orwarding

HTTP TCP IP ethernet Host A IP

ethernet

Router R

link

HTTP TCP IP ethernet Router W Host B IP

ethernet link

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P assenger Forwarding ☺

Tickets Baggage Gates Runway Syracuse Airport Gates

Runway

Newark

Runway

Tickets Baggage Gates Runway Chicago Boise Airport Gates

runway runway

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Tracerout e/ t racert

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Graphical Tracerout e (plus DNS inf ormat ion ☺)

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I nt ernet Map

Tracerout e gives one slice t hrough t he

I nt ernet t opology

What does t he I nt ernet really look like?

That is a act ually a har d quest ion t o answer I nt er net At las Pr oj ect

  • ht t p:/ / www.caida.org/ proj ect s/ int ernet at las/
  • Techniques, sof t ware, and prot ocols f or mapping t he

I nt ernet , f ocusing on I nt ernet t opology, perf ormance, workload, and rout ing dat a

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The I nt ernet around 1990

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CAI DA: NSFNET growt h unt il 1995

Backbone nodes elevat ed Low Tr af f ic Volume High

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NSF Net working Archit ect ure

  • f Lat e 1990s

NSFNET Backbone Proj ect successf ully

t ransit ioned t o a new net working archit ect ure in 1995.

vBNS ( ver y high speed Backbone Net wor k

Ser vices) - NSF f unded, provided by MCI

4 or iginal Net wor k Access Point s (NSF

awar ded)

NSF f unded Rout ing Ar bit er pr oj ect Net wor k Ser vice Pr ovider s (not NSF f unded)

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Net work Access P

  • int

Allows I nt ernet Service Providers (I SPs),

government , research, and educat ional

  • rganizat ions t o int erconnect and exchange

inf or mat ion

I SP

s connect t heir net works t o t he NAP f or t he purpose of exchanging t raf f ic wit h

  • t her I SPs

Such exchange of I nt ernet t raf f ic is of t en

ref erred t o as "peering"

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The I nt ernet in 1997

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CAI DA’s skit t er plot

Highly connect ed Few connect ions Locat ion (longit ude)

Skit t er dat a 16 monit or s pr obing appr oximat ely 400,000 dest inat ions 626,773 I P addr esses 1,007.723 I P links 48,302 (52%) of globally r out able net work pref ixes

Eur ope Nort h America Asia Top 15 ASes ar e in Nor t h Amer ica (14 in US, 1 in Canada) Many links US t o Asia and Eur ope; f ew dir ect Asia/ Eur ope Links

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DNS: Domain Name Syst em

People: many ident if iers:

SSN, name, P

assport #

I nt ernet host s, rout ers:

I P addr ess (32 bit )

  • used f or addressing

dat agrams

“name”, e.g.,

gaia.cs.umass.edu - used by humans

Q: map bet ween I P addr esses and name ? Domain Name Syst em:

dist ribut ed dat abase

implement ed in hierarchy of many name servers

applicat ion- layer prot ocol

host , rout ers, name servers t o communicat e t o resolve names (address/ name t ranslat ion)

not e: core I nt ernet

f unct ion implement ed as applicat ion- layer prot ocol

complexit y at net work’s

“edge”

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Names and addresses: why bot h?

Name: www.google.com I P addr ess (one of t hem): 216.239.39.147

(Also Et hernet or ot her link- layer addresses.)

I P addr esses ar e f ixed- size number s.

32 bit s. 216.239.39.147 =

101011000.11101111.00100111.10010011 Names are memor izable, f lexible:

Variable- lengt h Many names f or a single I P address. Change address doesn’t imply change name. iPv6 addresses are 128 bit – even harder t o memorize!

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Mapping Not 1 t o 1

One name may map t o more t han one I P

address

I P addr esses ar e per net wor k int er f ace Mult i -homed machines have mor e t han one

net wor k int er f ace - each wit h it s own I P address

Example: r out er s must be like t his

One I P

address may map t o more t han one name

One server machine may be t he web server

(www.f oo,com), mail server (mail.f oo.com)et c.

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How t o get names and numbers?

Acquisit ion of Names and numbers are bot h

regulat ed

Why?

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How t o get a name?

First , get a domain name t hen you are f ree

t o assign sub names in t hat domain

How t o get a domain name coming up

Bef or e you ask f or a domain name t hough

Should under st and domain name st r uct ur e… Know t hat you ar e r esponsible f or pr oviding

aut hor it at ive DNS ser ver (act ually a pr imar y and one or mor e secondar y DNS ser ver s) f or t hat domain and r egist r at ion inf or mat ion t hr ough “whois”

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Domain name st ruct ure

ccTLDs root (unnamed) com mil gov edu gr

  • rg

net fr uk us

... ...

clarkson ustreas second level (sub-)domains google gTLDs gTLDs= Generic Top Level Domains ccTLDs = Country Code Top Level Domains

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Top-level Domains (TLDs)

Generic Top Level Domains (gTLDs)

.com - commer cial or ganizat ions .or g - not-f or-pr of it or ganizat ions .edu - educat ional or ganizat ions .mil - milit ar y or ganizat ions .gov - gover nment al or ganizat ions .net - net wor k ser vice pr ovider s New: .biz, .inf o, .name, …

Count ry code Top Level Domains (ccTLDs)

One f or each count ry

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How t o get a domain name?

I n 1998, non-prof it corporat ion, I nt ernet

Corporat ion f or Assigned Names and Numbers (I CANN), was f ormed t o assume responsibilit y f rom t he US Government

I CANN aut horizes ot her companies t o regist er

domains in com, org and net and new gTLDs

Net wor k Solut ions is lar gest and in t r ansit ional per iod

bet ween US Govt and I CANN had sole aut hor it y t o r egist er domains in com, or g and net

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How t o get an I P Address?

Answer 1: Nor mally, answer is get an I P addr ess

f r om your upst r eam pr ovider

This is essent ial t o maint ain ef f icient rout ing!

Answer 2: I f you need lot s of I P addr esses t hen

you can acquir e your own block of t hem.

I P

address space is a scarce resource - must prove you have f ully ut ilized a small block bef ore can ask f or a larger one and pay $$ (J an 2002 - $2250/ year f or / 20 and $18000/ year f or a / 14)

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How t o get lot s of I P Addresses? I nt ernet Regist ries

RI PE NCC (Riseaux I P Eur opiens Net wor k Coor dinat ion Cent r e) f or Europe, Middle-East , Af r ica APNI C(Asia Pacif ic Net wor k I nf or mat ion Cent re )f or Asia and Pacif ic ARI N (Amer ican Regist r y f or I nt er net Number s) f or t he Amer icas, t he Car ibbean, sub

  • sahar an Af r ica

Not e: Once again r egional dist r ibut ion is impor t ant f or ef f icient r out ing! Can also get Aut onomous Syst em Numnber s (ASNs f rom t hese regist ries

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End-t o-End Example

  • Click ->

get page

  • page f r om local
  • r r emot e comput er
  • link:

ht t p:/ / www. cnn.com specif ies

  • pr ot ocol (ht t p)
  • locat ion

(www.cnn.com)

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Locat ing Resource

www.cnn.com is t he nam e of a comput er

(and, implicit ly, of a f ile in t hat comput er )

Use DNS t o t r anslat e

name t o addr ess

local com host cnn.com? cnn.com? IP = a.b.c.d IP = a.b.c.d

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Connect ion

The pr ot ocol (ht t p) set s up a connection (anot her

pr ot ocol, t cp) bet ween t he host and cnn.com t o t r ansf er t he page

The connect ion t r ansf er s t he page as a byt e

st r eam, wit hout er r or s: f low control + error control

Host cnn.com connect OK get page page; close

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Dat a f low

The byt e st r eam f lows

f r om end t o end acr oss many links and swit ches: rout ing (+ addressing)

That st r eam is r egulat ed

and cont rolled by bot h ends: ret ransmission of er r oneous or missing byt es; f low cont rol

HOST CNN.COM

end-to-end pacing and error control routing

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P acket s

The net wor k

t r anspor t s byt es gr ouped int o packet s

The packet s ar e “self-

cont ained” and r out er s handle t hem one by

  • ne

The end host s wor r y

about er r or s and pacing

Dest inat ion sends ACKs Source checks losses

C

HOST: B CNN.COM: A A | B | # , CRC | bytes B: to C

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P

  • rt Numbers

When a packet arrives at it s dest inat ion,

t he operat ing syst em uses t he dest inat ion port number t o ident if y which applicat ion should receive it .

This is called demult iplexing.

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Bit s

Equipment in each node sends t he packet s as a

st ring of bit s

That equipment is not awar e of t he meaning of

t he bit s

01011...011...110 Transmitter Physical Medium Receiver 01011...011...110 Optical Copper Wireless