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CS6250 - COMPUTER NETWORKS
What=are=advantages=and=disadvantages=of=a=layered=architecture?=-=ans- ✔✔Separation=of=concerns=among=logical=layers=promotes=flexibility,=scalibility,=and=m aintainability.=Multiple=applications=can=reuse=the=components.=It=enables=teams=to=wo rk=on=different=parts=with=minimal=dependencies=on=other=teams What=are=the=similarities=of=the=OSI=model=and=five-layered=Internet=model?=-=ans- ✔✔They=are=both=based=on=layered=architecture. The=are=comparable=to=each=other=-=see=image= 1 Both=are=networking=standards What=are=the=differences=of=the=OSI=model=and=five-layered=Internet=model?=-=ans- ✔✔OSI=is=a=generic=model=based=on=the=functions=of=each=layer.=TCP=is=a=protocol=o riented=standard.= OSI=uses= 3 =upper=layers=(application,=presentation,=and=session)=while=TCP=just=uses =application. Likewise,=OSI=uses= 2 =Lower=layers=(Physical=and=DataLink)=while=TCP=just=uses=Link What=is=a=socket?=-=ans-✔✔A=socket=is=one=endpoint=of=a=two- way=communication=link=between=two=programs=running=on=the=network. A=socket=is=bound=to=a=port=number=so=that=the=TCP=layer=can=identify=the=application =that=data=is=destined=to=be=sent=to. Physical=Layer=-=ans- ✔✔The=lowest,=or=first,=layer=of=the=OSI=model.=Protocols=in=this=layer=generate=and= detect=signals=so=as=to=transmit=and=receive=data=over=a=network=medium.=These=prot ocols=also=set=the=data=transmission=rate=and=monitor=data=error=rates,=but=do=not=pro vide=error=correction. The=lowest=layer=of=the=OSI=Model=is=concerned=with=electrically=or=optically=transmitti ng=raw=unstructured=data=bits=across=the=network=from=the=physical=layer=of=the=sendi ng=device=to=the=physical=layer=of=the=receiving=device.=It=can=include=specifications=s uch=as=voltages,=pin=layout,=cabling,=and=radio=frequencies.=At=the=physical=layer,=one
=might=find="physical"=resources=such=as=network=hubs,=cabling,=repeaters,=network=a dapters=or=modems. OSI=Data=Link=Layer=-=ans- ✔✔At=the=data=link=layer,=directly=connected=nodes=are=used=to=perform=node-to- node=data=transfer=where=data=is=packaged=into=frames.=The=data=link=layer=also=corr ects=errors=that=may=have=occurred=at=the=physical=layer. The=data=link=layer=encompasses=two=sub- layers=of=its=own.=The=first,=media=access=control=(MAC),=provides=flow=control=and=m ultiplexing=for=device=transmissions=over=a=network.=The=second,=the=logical=link=contr ol=(LLC),=provides=flow=and=error=control=over=the=physical=medium=as=well=as=identifi es=line=protocols. OSI=Network=Layer=-=ans- ✔✔The=network=layer=is=responsible=for=receiving=frames=from=the=data=link=layer,=an d=delivering=them=to=their=intended=destinations=among=based=on=the=addresses=cont ained=inside=the=frame.=The=network=layer=finds=the=destination=by=using=logical=addre sses,=such=as=IP=(internet=protocol).=At=this=layer,=routers=are=a=crucial=component=us ed=to=quite=literally=route=information=where=it=needs=to=go=between=networks. OSI=Transport=Layer=-=ans- ✔✔The=transport=layer=manages=the=delivery=and=error=checking=of=data=packets.=It=r egulates=the=size,=sequencing,=and=ultimately=the=transfer=of=data=between=systems=a nd=hosts.=One=of=the=most=common=examples=of=the=transport=layer=is=TCP=or=the=Tr ansmission=Control=Protocol. OSI=Session=Layer=-=ans- ✔✔The=session=layer=controls=the=conversations=between=different=computers.=A=sess ion=or=connection=between=machines=is=set=up,=managed,=and=termined=at=layer=5.=S ession=layer=services=also=include=authentication=and=reconnections. OSI=Presentation=Layer=-=ans- ✔✔The=presentation=layer=formats=or=translates=data=for=the=application=layer=based= on=the=syntax=or=semantics=that=the=application=accepts.=Because=of=this,=it=at=times=a lso=called=the=syntax=layer.=This=layer=can=also=handle=the=encryption=and=decryption= required=by=the=application=layer. OSI=Application=Layer=-=ans- ✔✔At=this=layer,=both=the=end=user=and=the=application=layer=interact=directly=with=the =software=application.=This=layer=sees=network=services=provided=to=end- user=applications=such=as=a=web=browser=or=Office=365.=The=application=layer=identifie s=communication=partners,=resource=availability,=and=synchronizes=communication.
End=to=End=Principle=Example=-=ans-✔✔An=example=of=the=end-to- end=principle=is=that=of=an=arbitrarily=reliable=file=transfer=between=two=endpoints=in=a= distributed=network=of=a=varying,=nontrivial=size: [3]=The=only=way=two=endpoints=can=obtain=a=completely=reliable=transfer=is=by=transm itting=and=acknowledging=a=checksum=for=the=entire=data=stream;=in=such=a=setting,=le sser=checksum=and=acknowledgment=(ACK/ NACK)=protocols=are=justified=only=for=the=purpose=of=optimizing=performance=- =they=are=useful=to=the=vast=majority=of=clients,=but=are=not=enough=to=fulfill=the=reliabili ty=requirement=of=this=particular=application.=A=thorough=checksum=is=hence=best=done =at=the=endpoints,=and=the=network=maintains=a=relatively=low=level=of=complexity=and= reasonable=performance=for=all=clients What=is=the=EvoArch=model?=-=ans- ✔✔an=hourglass=model=that=consists=of=six=protocol=and=application=layers=that=origin ate=from=a=single=bubble=-=IPv What=are=the=ramifications=of=the=hourglass=shape=of=the=internet=-=ans-✔✔ Repeater=-=ans-✔✔Physical=Layer=- =A=repeater=operates=at=the=physical=layer.=Its=job=is=to=regenerate=the=signal=over=the =same=network=before=the=signal=becomes=too=weak=or=corrupted=so=as=to=extend=the =length=to=which=the=signal=can=be=transmitted=over=the=same=network.=An=important= point=to=be=noted=about=repeaters=is=that=they=do=not=amplify=the=signal.=When=the=si gnal=becomes=weak,=they=copy=the=signal=bit=by=bit=and=regenerate=it=at=the=original=s trength.=It=is=a= 2 =port=device. Hub=-=ans-✔✔Physical=Layer=- =A=hub=is=basically=a=multiport=repeater.=A=hub=connects=multiple=wires=coming=from=d ifferent=branches,=for=example,=the=connector=in=star=topology=which=connects=differen t=stations.=Hubs=cannot=filter=data,=so=data=packets=are=sent=to=all=connected=devices. =In=other=words,=collision=domain=of=all=hosts=connected=through=Hub=remains=one.=Al so,=they=do=not=have=intelligence=to=find=out=best=path=for=data=packets=which=leads=t o=inefficiencies=and=wastage. Bridge=-=ans-✔✔Data=Link=Layer=- =A=bridge=is=a=repeater,=with=add=on=the=functionality=of=filtering=content=by=reading=th e=MAC=addresses=of=source=and=destination.=It=is=also=used=for=interconnecting=two=L ANs=working=on=the=same=protocol.=It=has=a=single=input=and=single=output=port,=thus= making=it=a= 2 =port=device. Switch=-=ans-✔✔Data=Link=Layer=- =A=switch=is=a=multiport=bridge=with=a=buffer=and=a=design=that=can=boost=its=efficiency (a=large=number=of=ports=imply=less=traffic)=and=performance.=A=switch=is=a=data=link=l ayer=device.=The=switch=can=perform=error=checking=before=forwarding=data,=that=mak
es=it=very=efficient=as=it=does=not=forward=packets=that=have=errors=and=forward=good= packets=selectively=to=correct=port=only.=In=other=words,=switch=divides=collision=domai n=of=hosts,=but=broadcast=domain=remains=same. Router=-=ans-✔✔Network=Layer=- =A=router=is=a=device=like=a=switch=that=routes=data=packets=based=on=their=IP=address es.=Router=is=mainly=a=Network=Layer=device.=Routers=normally=connect=LANs=and=W ANs=together=and=have=a=dynamically=updating=routing=table=based=on=which=they=ma ke=decisions=on=routing=the=data=packets.=Router=divide=broadcast=domains=of=hosts=c onnected=through=it. What=is=a=bridge,=and=how=does=it="learn"=-=ans-✔✔Data=Link=Layer=Device=-= bridge=need=to=learn=which=computers=are=connected=to=which=of=its=LAN=interfaces.= More=formally,=it=need=to=learn=the=set=of=source=address=that=are=received=on=each=i nterface.=The=source=address=of=each=received=frame=is=recorded=in=the=address=tabl e,=together=with=the=port=on=which=the=frame=was=received.=This=is=called=learning Used=to=bridge=connections What=is=a=distributed=algorithm?=-=ans- ✔✔A=distributed=algorithm=is=one=that=is=divided=in=several=processors,=so=that=some= part=of=the=algorithm=is=run=on=one=processor,=other=part=in=another=processor,=and=s o=forth. Typically=data=is=partitioned=in=advance=so=that=each=processor=doesn't=need=to=wait=f or=the=output=of=another=processor,=but=that=is=not=always=feasable,=and=their=is=some =form=of=communication=between=processors. Now=something=important:=If=the=processors=share=memory=(RAM),=it=means=they=run =on=the=same=machine=and=it=is=called=parallel=algorithm.=If=they=run=on=different=boxe s,=it=means=they=need=a=communication=medium=like=a=network=cable=and=they=are=c alled=distrobuted=algorithms. Why=make=that=distinction Spanning=Tree=Algorithm=-=ans-✔✔ What=does=the=transport=layer=provide=-=ans-✔✔4th=Layer=in=OSI=Model It=provides=logical=communication=between=application=processes=running=on=different= hosts=within=a=layered=architecture=of=protocols=and=other=network=components In=a=nutshell,=the=transport=layer=collects=message=segments=from=applications,=and=tr ansmits=them=into=the=network=(Layer=3).=Here=the=segments=are=reassembled=into=ful ly-fledged=messages,=and=passed=on=to=Layer= 7 The=transport=layer=is=also=responsible=for=the=management=of=error=correction,=provid ing=quality=and=reliability=to=the=end=user.
What=is=multiplexing,=and=why=is=it=necessary=-=ans- ✔✔Multiplexing=reduces=the=number=of=physical=communication=links=needed=betwee n=two=points Think=about=how=TV=channels=that=stream=on=different=frequencies=all=come=in=on=the =same=line. Multiplexing=basically=involves=taking=multiple=signals=and=combining=them=into=one=si gnal=for=transmission=over=a=single=medium,=such=as=a=telephone=line.=The=input=sign als=can=be=either=analog=or=digital.=The=purpose=of=multiplexing=is=to=enable=signals=t o=be=transmitted=more=efficiently=over=a=given=communication=channel,=thereby=decre asing=transmission=costs. Time=Division=Multiplexing=(TDM)=-=ans-✔✔Almost=like=round-robin=-= each=input=signal=(or=data=stream)=is=assigned=a=fixed- length=time=slot=on=a=communication=channel.=Each=sender=transmits=a=block=of=data= during=its=assigned=time=slot. For=example,=let's=say=that=input=streams=from=three=sending=devices=are=being=multi plexed=into=one=signal=for=transmission=over=a=single=physical=channel.=Device= 1 =trans mits=a=block=of=data=during=time=slot=1,=device= 2 =transmits=a=block=of=data=during=time =slot=2,=and=device= 3 =transmits=a=block=of=data=during=time=slot=3.=After=device= 3 =tran smits,=the=cycle=begins=again=with=each=device=transmitting=in=turn=in=its=assigned=tim e=slot. A=drawback=to=standard=TDM=is=that=each=sending=device=has=a=reserved=time=slot=in =each=cycle,=regardless=of=whether=it=is=ready=to=transmit.=This=can=result=in=empty=sl ots=and=underutilization=of=the=multiplexed=communication=channel. Frequency=Division=Multiplexing=(FDM)=-=ans-✔✔Radio=/=Cable=TV=- =Mainly=used=in=Analog Can=be=used=over=both=wired=and=wireless each=signal=is=assigned=its=own=frequency=range=(or=channel)=within=a=larger=frequenc y=band.=Frequency=ranges=for=channels=cannot=overlap.=Frequency=bands=are=often=s eparated=by=an=unused=block=of=the=frequency=spectrum=to=reduce=interference. Code=Division=Multiplexing=(CDM)=-=ans- ✔✔signals=from=multiple=senders=are=transmitted=in=an=assigned=frequency=band.=CD M=uses=a=principle=known=as=spread=spectrum,=in=which=transmitted=signals=are=sprea d=out=over=all=frequency=channels=in=the=assigned=band. In=simplest=terms,=each=signal=in=a=CDM=system=is=multiplexed=by=means=of=a=spread ing=code=assigned=to=the=sender.=This=spreading=code=modulation=increases=the=band
width=required=for=the=signal.=The=receiver=is=aware=of=the=spreading=code=and=uses=i t=to=demultiplex=the=signal. Although=it=increases=the=bandwidth=needed=for=transmission,=CDM=has=the=advantag e=of=being=more=secure=than=other=types=of=multiplexing.=In=CDM=transmissions,=an=in dividual=user's=signal=is=mixed=in=with=the=signals=of=other=users=in=the=frequency=ban d.=Without=the=spreading=code=required=for=demultiplexing=an=individual=signal,=CDM=t ransmissions=appear=merely=to=be=noise=to=a=receiving=device. CDM=is=used=in=cellular=telephone=systems. What=are=the=differences=between=UDP=and=TCP=-=ans-✔✔TCP=- =Transmission=Control=Protocol reliable=transport=-=slower=because=of=the=reliability UDP=-=User=Datagram=Protocol=- =like=sending=a=letter=in=the=mail.=You=know=you=sent=it,=but=that's=it.=The=receiver=isn't =aware,=you=don't=know=what=happened=in=the=end=-=it=was=just=sent. Quicker=but=less=reliable When=would=an=application=layer=protocol=choose=UDP=over=TCP=-=ans- ✔✔UDP=is=used=when=speed=is=preferred=over=integrity=and=error=correction.=Some=c ommon=applications=include=streaming=video=and=music,=live=broadcasts,=voice=and=vi deo=calling=(VoIP),=and=online=gaming.=In=these=scenarios,=it=doesn't=really=matter=if=y ou=lose=the=occasional=video=frame=or=button=press,=which=favors=UDP.=DNS=traffic=is =usually=exchanged=over=the=UDP=protocol. Explain=the=TCP=Three-way=Handshake=-=ans- ✔✔Step= 1 =(SYN)=:=In=the=first=step,=client=wants=to=establish=a=connection=with=server ,=so=it=sends=a=segment=with=SYN(Synchronize=Sequence=Number)=which=informs=ser ver=that=client=is=likely=to=start=communication=and=with=what=sequence=number=it=start s=segments=with Step= 2 =(SYN=+=ACK):=Server=responds=to=the=client=request=with=SYN- ACK=signal=bits=set.=Acknowledgement(ACK)=signifies=the=response=of=segment=it=rec eived=and=SYN=signifies=with=what=sequence=number=it=is=likely=to=start=the=segments =with Step= 3 =(ACK)=:=In=the=final=part=client=acknowledges=the=response=of=server=and=they= both=establish=a=reliable=connection=with=which=they=will=start=the=actual=data=transfer TCP=Connection=Teardown=-=ans-✔✔Step= 1 =(FIN=From=Client)=- =Suppose=that=the=client=application=decides=it=wants=to=close=the=connection.=(Note=t hat=the=server=could=also=choose=to=close=the=connection).=This=causes=the=client=sen
ransmission=of=packets=that=are=found=to=be=corrupted=or=lost=during=the=transmission =process. Stop=and=Wait=ARQ=-=ans-✔✔A=stop-and- wait=ARQ=sender=sends=one=frame=at=a=time;=it=is=a=special=case=of=the=general=slidin g=window=protocol=with=transmit=and=receive=window=sizes=equal=to=one=in=both=cases .=After=sending=each=frame,=the=sender=doesn't=send=any=further=frames=until=it=receiv es=an=acknowledgement=(ACK)=signal.=After=receiving=a=valid=frame,=the=receiver=sen ds=an=ACK.=If=the=ACK=does=not=reach=the=sender=before=a=certain=time,=known=as=th e=timeout,=the=sender=sends=the=same=frame=again.=The=timeout=countdown=is=reset= after=each=frame=transmission. Go=Back=N=ARQ=-=ans-✔✔Go=-=Back=- =N=ARQ=provides=for=sending=multiple=frames=before=receiving=the=acknowledgment=f or=the=first=frame.=The=frames=are=sequentially=numbered=and=a=finite=number=of=fram es.=The=maximum=number=of=frames=that=can=be=sent=depends=upon=the=size=of=the= sending=window.=If=the=acknowledgment=of=a=frame=is=not=received=within=an=agreed= upon=time=period,=all=frames=starting=from=that=frame=are=retransmitted. Selective=Acking=-=ans-✔✔SACKs=allow=a=receiver=to=acknowledge=non- consecutive=data,=so=that=the=sender=can=retransmit=only=what=is=missing=at=the=recei ver�s=end.=This=is=particularly=helpful=on=paths=with=a=large=bandwidth- delay=product=(BDP) Fast=Retransmit=-=ans- ✔✔if=a=receiver=receives=a=data=segment=that=is=out=of=order,=it=immediately=sends=a= duplicate=acknowledgement=to=the=sender.=If=the=sender=receives=three=duplicate=ackn owledgements,=it=assumes=that=the=data=segment=indicated=by=the=acknowledgements =is=lost=and=immediately=re- transmits=the=lost=segment.=With=FRR,=time=is=not=lost=waiting=for=a=timeout=in=order=f or=re-transmission=to=begin. what=is=flow=control=-=ans- ✔✔In=data=communications,=flow=control=is=the=process=of=managing=the=rate=of=data= transmission=between=two=nodes=to=prevent=a=fast=sender=from=overwhelming=a=slow= receiver.=It=provides=a=mechanism=for=the=receiver=to=control=the=transmission=speed,= so=that=the=receiving=node=is=not=overwhelmed=with=data=from=transmitting=node.=Flow =control=should=be=distinguished=from=congestion=control,=which=is=used=for=controlling =the=flow=of=data=when=congestion=has=actually=occurred Congestion=Control=-=ans- ✔✔What=you=do=to=prevent=networks=from=congesting.=Leaky=bucket=algorithm Goals=of=congestion=control=-=ans-✔✔1.=User=network=resources=efficiently
2.=Avoid=congestion=collapse Network=Assisted=Congestion=Control=-=ans- ✔✔routers=provide=feedback=to=end=systems E2E=Congestion=COntrol=-=ans-✔✔ How=does=a=host=infer=congestion=-=ans-✔✔End-system=observers=loss=or=delay How=to=calculate=TCP=throughput=-=ans-✔✔ Differences=between=forwarding=and=routing=-=ans- ✔✔Routing=is=the=decision=over=which=interface=a=packet=is=to=be=sent.=This=decision= has=to=be=made=for=locally=created=packets,=too.=Routing=tables=contain=network=addr esses=and=the=associated=interface=or=nexthop.=This=refers=to=ip=route=and=ip=rule=(in= a=Linux=context) Forwarding=refers=to=packets=which=reach=a=system=but=are=not=destined=for=this=syst em.=Forwarding=is=a=decision=of=the=system:="I=take=the=packet=and=try=to=get=it=towar ds=its=destination."=Instead=of=just=dropping=it.="forwarding"=is=a=common=term=in=the=c ontext=of=packet=filters.=Linux'=Netfilter=has=three=chains=in=its=base=table:=INPUT,=OU TPUT,=and=FORWARD.=This=chain=just=makes=the=decision="Shall=this=packet=be=forw arded=or=dropped?"=(if=forwarding=is=generally=enabled=on=the=system;=Linux=again:=/ proc/sys/net/ipv4/ip_forward) Link=state=algorithm=-=ans-✔✔The=basic=idea=of=link- state=routing=protocols=is=that=each=node=sends=local=topology=information=to=its=neigh bors.=This=information=then=is=propagated=using=sophisticated="flooding"=mechanisms=t hrough=the=network Computational=Complexity=of=LS=Algorithm=-=ans-✔✔O(n^2) What=is=the=computation=complexity=of=this=algorithm? =That=is,=given=n=nodes=(not=counting=the=source),=how=much=computation=must=be=d one=in=the=worst=case=to=find=the=least=cost=paths=from=the=source=to=all=destinations? =In=the=first=iteration,=we=need=to=search=through=all=n=nodes=to=determine=the=node,= w,=not=in=N=that=has=the=minimum=cost.=In=the=second=iteration,=we=need=to=check=n− 1 =nodes=to=determine=the=minimum=cost;=in=the=third=iteration=n−2=nodes=and=so=on.= Overall,=the=total=number=of=nodes=we=need=to=search=through=over=all=the=iterations=i s=n*(n+1)/ 2,=and=thus=we=say=that=the=above=implementation=of=the=link=state=algorithm=has=wor st=case=complexity=of=order=n=squared:=O(n2).=(A=more=sophisticated=implementation= of=this=algorithm,=using=a=data=structure=known=as=a=heap,=can=find=the=minimum=in=li ne= 9 =in=logarithmic=rather=than=linear=time,=thus=reducing=the=complexity).
All=routers=exchange=link- states=by=means=of=flooding.=Each=router=that=receives=a=link- state=update=should=store=a=copy=in=its=link- state=database=and=then=propagate=the=update=to=other=routers. After=the=database=of=each=router=is=completed,=the=router=calculates=a=Shortest=Path =Tree=to=all=destinations.=The=router=uses=the=Dijkstra=algorithm=in=order=to=calculate=t he=shortest=path=tree.=The=destinations,=the=associated=cost=and=the=next=hop=to=reac h=those=destinations=form=the=IP=routing=table. In=case=no=changes=in=the=OSPF=network=occur,=such=as=cost=of=a=link=or=a=network= being=added=or=deleted,=OSPF=should=be=very=quiet.=Any=changes=that=occur=are=co mmunicated=through=link- state=packets,=and=the=Dijkstra=algorithm=is=recalculated=in=order=to=find=the=shortest=p ath. The=algorithm=places=each=router=at=the=root=of=a=tree=and=calculates=the=shortest=pat h=to=each=destination=based=on=the=cumulative=cost=required=to=reach=that=destination .=Each=router=will=have=its=own=view=of=the=topology=even=though=all=the=routers=will=b uild=a=shortest=path=tree=using=the=same=link- state=database.=The=following=sections=indicate=what=is=involved=in=building=a=shortest =path=tr How=does=a=router=process=advertisements?=-=ans- ✔✔It=updates=it's=own=table=and=then=broadcast=to=all=nodes=in=it's=network=the=chang es What=is=hot=potato=routing=-=ans- ✔✔A=form=of=routing=in=which=the=nodes=of=a=network=have=no=buffer=to=store=packet s=in=before=they=are=moved=on=to=their=final=predetermined=destination.=In=normal=routi ng=situations,=when=multiple=packets=contend=for=a=single=outgoing=channel,=packets=t hat=are=not=buffered=are=dropped=to=avoid=congestion.=But=in=hot=potato=routing,=each =packet=that=is=routed=is=constantly=transferred=until=it=reaches=its=final=destination=bec ause=the=individual=communication=links=can=not=support=more=than=one=packet=at=a=ti me.=The=packet=is=bounced=around=like=a="hot=potato,"=sometimes=moving=further=aw ay=from=its=destination=because=it=has=to=keep=moving=through=the=network.=This=tech nique=allows=multiple=packets=to=reach=their=destinations=without=being=dropped.=This= is=in=contrast=to="store=and=forward"=routing=where=the=network=allows=temporary=stor age=at=intermediate=locations.=Hot=potato=routing=has=applications=in=optical=networks= where=messages=made=from=light=can=not=be=stored=in=any=medium. Describe=the=relationships=between=ISPs,=IXPs,=and=CDNs=-=ans- ✔✔An=Internet=exchange=point=(IXP)=is=a=physical=location=through=which=Internet=infr astructure=companies=such=as=Internet=Service=Providers=(ISPs)=and=CDNs=connect=w ith=each=other.=These=locations=exist=on=the="edge"=of=different=networks,=and=allow=n
etwork=providers=to=share=transit=outside=their=own=network.=By=having=a=presence=ins ide=of=an=IXP=location,=companies=are=able=to=shorten=their=path=to=the=transit=coming =from=other=participating=networks,=thereby=reducing=latency,=improving=round- trip=time,=and=potentially=reducing=costs. What=is=an=autonomous=system?=-=ans- ✔✔An=autonomous=system=(AS)=is=a=collection=of=connected=Internet=Protocol=(IP)=ro uting=prefixes=under=the=control=of=one=or=more=network=operators=on=behalf=of=a=sing le=administrative=entity=or=domain=that=presents=a=common,=clearly=defined=routing=pol icy=to=the=internet How=does=an=Autonomous=System=determine=what=rules=to=import/export?=-=ans- ✔✔The=business=relationships=between=different=AS's=determine=the=rules=etc.= The=first=form=is=provider- customer=transit=(aka="transit"),=wherein=one=ISP=(the="provider"=P=in=Figure=3)=provid es=access=to=all=(or=most)=destinations=in=its=routing=tables.=Transit=almost=always=is= meaningful=in=an=inter- AS=relationship=where=financial=settlement=is=involved;=the=provider=charges=its=custo mers=for=Internet=access,=in=return=for=forwarding=packets=on=behalf=of=customers=to=d estinations=(and=in=the=opposite=direction=in=many=cases).=Another=example=of=a=trans it=relationship=in=Figure= 3 =is=between=X=and=its=customers=(the=Cis).=The=second=prev alent=form=of=inter- AS=interconnection=is=called=peering.=Here,=two=ASes=(typically=ISPs)=provide=mutual= access=to=a=subset=of=each=other's=routing=tables.=The=subset=of=interest=here=is=their =own=transit=customers=(and=the=ISPs=own=internal=addresses).=Like=transit,=peering=is =a=business=deal,=but=it=may=not=involve=financial=settlement.=While=paid=peering=is=co mmon=in=some=parts=of=the=world,=in=many=cases=they=are=reciprocal=agreements.=As =long=as=the=traffic=ratio=between=the=concerned=ASs=is=not=highly=asymmetric Original=Goals=of=BGP=-=ans- ✔✔BGP=was=originally=designed=for=scalability,=policy=(the=ability=for=each=AS=to=impl ement=and=enforce=various=forms=of=routing=policies)=and=cooperation=under=competiti ve=circumstances Security=was=considered=later=because=of=the=need=of=the=protocol Two=types=of=BGP=sessions=-=ans-✔✔eBGP=-=sessions=betweeon=BGP- speaking=routers=in=different=autonomous=systems iBGP===sessions=between=BGP=speaking=routers=in=the=same=autonomous=systems eBGP=is=the="STANDARD"=mode=in=which=BGP=is=used=- =the=original=reason=it=was=designed=was=to=exchange=routing=information=between=di fferent=ASes=in=the=internet.
time=cost=for=establishing=the=connection,=monthly=charge=for=using=the=chosen=IXP=p ort=(those=with=higher=speeds=are=more=expensive)=and=perhaps=an=annual=fee=of=me mbership=in=the=entity=owning=and=operating=the=IXP.=However,=the=IXPs=do=not=usua lly=charge=based=on=the=amount=of=exchanged=volume.=They=also=do=not=usually=inter fere=with=bilateral=relations=between=the=participants=unless=there=is=a=violation=of=the= GTC.=Even=with=the=set- up=costs,=IXPs=are=usually=cheaper=than=other=conventional=methods=of=exchanging=tr affic=(such=as=relying=on=third=parties=which=charge=based=on=the=volume=of=exchange d=traffic).=IXP=participants=also=often=experience=better=network=performance=and=QoS =because=of=reduced=delays=and=routing=efficiencies.=In=addition,=many=companies=tha t=are=major=players=in=the=Internet=space=(such=as=Google)=incentivize=other=networks =to=connect=at=IXPs=by=making=it=a=requirement=to=peering=with=them. Private=Peering: Most=operational=IXPs=also=provide=a=private=peering=service=(Private=Interconnects=- =PIs)=that=allow=direct=traffic=exchange=between=two=parties=of=a=PI=and=don't=use=the =IXP's=public=peering=infrastructure.=This=is=commonly=used=when=the=participants=wa nt=a=well-provisioned=dedicated=link=capable=of=handling=high- volume,=bidirectional=and=relatively=stable=traffic. Route=Servers=and=Service=Level=Agreements: Many=IXPs=also=include=service=level=agreements=(SLAs)=and=free=use=of=the=IXP's=ro ute=servers=for=participants.=This=allows=participants=to=arrange=instant=peering=with=a= large=number=of=c how=do=route=servers=work=-=ans- ✔✔A=route=server=is=a=computer=server=that=was=originally=developed=by=the=Routing= Arbiter=project,=with=funding=from=the=National=Science=Foundation.=This=routing=proce ss=directs=information=among=Border=Gateway=Protocol=(BGP)=routers.=These=servers =are=placed=at=Network=access=points=(NAPs),=where=centralized=computers=organize= and=match=routing=data.=Route=servers=are=important=because=they=help=manage=BG P=sessions.=BGP=sessions=have=difficulties=with=overhead=when=managing=sessions= where=routers=with=single=and=multiple=domains=are=connected=(also=known=as=full=me sh=routing=connectivity).=Route=servers=reduce=overhead=by=referencing=the=IP=routing =table=of=an=autonomous=system=where=the=server=is=located. What=are=the=basic=components=of=a=router=-=ans-✔✔interface processor internetwork=operating=system=(IOS) RAM NVRAM ROM Flash=Memory Configuration=Register Buses
Explain=the=forwarding=(or=switching)=function=of=a=router=-=ans- ✔✔A=primary=function=of=a=router=is=to=forward=packets=toward=their=destination.=This= is=accomplished=by=using=a=switching=function,=which=is=the=process=used=by=a=router =to=accept=a=packet=on=one=interface=and=forward=it=out=another=interface.=A=key=resp onsibility=of=the=switching=function=is=to=encapsulate=packets=in=the=appropriate=data=li nk=frame=type=for=the=outgoing=data=link. Output=Port=-=ans- ✔✔An=output=port=stores=the=datagrams=that=have=been=forwarded=to=it=through=the=s witching=fabric,=and=then=transmits=the=datagrams=on=the=outgoing=link.=The=output=po rt=thus=performs=the=reverse=data=link=and=physical=layer=functionality=as=the=input=por t. Input=Port=-=ans-✔✔performs=the=physical=and=data- link=functions=of=the=packet=switch What=is=the=purpose=of=the=router's=control=plane=-=ans- ✔✔Control=plane=refers=to=all=the=functions=and=processes=that=determine=which=path =to=use.=Routing=protocols,=spanning=tree,=ldp,=etc=are=examples What=tasks=occur=in=a=router=-=ans-✔✔Providing=a=router=hostname Setting=up=passwords Disabling=DNS=lookup Setting=up=logging Setting=timestamps=for=logging=and=debugging Defining=console,=auxiliary,=and=virtual=terminal=settings Setting=up=a=Comm=Server=to=access=your=routers=more=easily Handling=password=recovery Downloading=a=software=image=from=a=TFTP=server File=management=tasks interconnection=network=-=ans- ✔✔An=interconnection=network=can=forward=packets=in=parallel=as=long=as=all=the=pac kets=are=being=forwarded=to=different=output=ports. Circuit=Switching=-=ans-✔✔In=Circuit=Switching=a=dedicated=link/ path=is=established=across=the=sender=and=the=receiver=which=is=maintained=for=the=en tire=duration=of=conversation. Circuit=Switching=is=generally=used=in=the=public=networks.=It=come=into=existence=for= handling=voice=traffic=in=addition=to=digital=data.=How=ever=digital=data=handling=by=the =use=of=circuit=switching=methods=are=proved=to=be=inefficient.=The=network=for=Circuit= Switching=is=shown=in=figure.
2.=KEEPALIVE:=These=messages=are=exchanged=to=keep=a=current=session=going Flap=Damping=-=ans- ✔✔an=AS=will=track=the=number=of=updates=to=a=specific=prefix=over=a=certain=amount =of=time.=If=the=tracked=value=reaches=a=configurable=value,=the=AS=can=suppress=that =route=until=a=later=time.
