CS 6250 COMPUTER NETWORKS
EXAM 2
What=are=the=main=components=of=a=router?=-=ans-✔✔-Input/Output=ports
-The=switching=fabric
-The=routing=processor
What=do=the=input=ports=do=for=a=router?=-=ans-✔✔-Line=termination
-Data=link=processing=unit=decapsulate=the=packets
-
Checks=with=the=forwarding=table=to=ensure=each=packet=is=forwarded=to=the=appropri
ate=output=port
What=does=the=switching=fabric=do?=-=ans-
✔✔Moves=packets=from=input=to=output=ports.=3=Types:=memory,=bus,=and=crossbar
What=do=the=output=ports=do?=-=ans-
✔✔Receive=and=queue=the=packets=that=come=from=the=switching=fabric=and=send=the
m=over=to=the=outgoing=link
Routers=control=plane=functions=-=ans-
✔✔implements=routing=protocols,=maintains=the=routing=tables,=computers=the=forward
ing=table
Router=Lookup=(Task=1=of=6)=-=ans-
✔✔When=a=packet=arrives,=router=looks=at=the=destination=IP=address=and=determines
=the=output=link=by=looking=at=the=forwarding=table=or=FIB.
Router=Switching=(Task=2=of=6)=-=ans-
✔✔After=lookup,=the=switching=system=takes=over=to=transfer=the=packet=from=the=inpu
t=link=to=the=output=link
, Router=Queueing=(Task=3=of=6)=-=ans-
✔✔After=switching,=it=will=need=to=be=queued=if=the=link=is=congested.=The=queue=may
be=simple=as=FIFO=or=some=other=algorithm
Router=Header=validation=and=checksum=(4=of=6)=-=ans-
✔✔The=router=checks=the=packet's=version=number,=decrements=the=time-to-
live=field,=and=recalculates=the=header=checksum
Router=Processing=(Task=5=of=6)=-=ans-
✔✔The=routers=build=their=forwarding=tables=using=routing=protocols=such=as=RIP,=OS
PF,=BGP=-=they=are=implemented=in=the=routing=processors
Protocol=Processing=(Task=6=of=6)=-=ans-
✔✔The=routers,=in=order=to=implement=their=functions,=need=to=implement=the=followin
g=protocols:
-
Simple=Network=Management=Protocol=which=provides=counters=for=remote=inspection
-TCP=and=UDP=for=remote=communication=with=the=router
-Internet=Control=Message=Protocol=for=sending=error=messages
Switching=via=memory=-=ans-
✔✔The=ports=operate=as=I/
O=devices=in=an=operating=system.=When=an=input=port=receives=a=packet,=it=sends=an
=interrupt=to=the=routing=processor=and=the=packet=is=coped=to=the=processors=memor
y.=Process=extracts=address=and=looks=to=table=to=find=output=port.=Then=its=copied=to
=the=output=port=buffer
Switching=via=bus=-=ans-
✔✔When=input=receives=a=packet,=it=puts=an=internal=header=that=designates=the=outp
ut=port,=and=sends=it=to=a=shared=bus.=All=output=ports=will=receive=the=packet,=but=onl
y=the=designated=one=will=keep=it.=Speed=of=the=bus=limits=the=speed=of=the=router.
Switching=via=Interconnection=network=-=ans-
✔✔Interconnect=network=that=connects=N=input=ports=to=N=output=ports=using=2N=buse
s.=Can=carry=multiple=packets=at=a=time
Bandwidth=and=Internet=population=scaling=(problem=1=of=2=that=routers=face)=-=ans-
✔✔Caused=by:
1.=Increasing=number=of=devices
2.=increasing=volumes=of=network=traffic=due=to=new=applications
3.=new=technologies=such=as=optical=links=that=can=accommodate=higher=volumes=of=tr
affic
Services=at=high=speeds=(problem=2=of=2=that=routers=face)=-=ans-
✔✔New=applications=require=services=such=as=protection=against=delays=during=conge
stion,=and=protection=during=attacks=or=failures.
EXAM 2
What=are=the=main=components=of=a=router?=-=ans-✔✔-Input/Output=ports
-The=switching=fabric
-The=routing=processor
What=do=the=input=ports=do=for=a=router?=-=ans-✔✔-Line=termination
-Data=link=processing=unit=decapsulate=the=packets
-
Checks=with=the=forwarding=table=to=ensure=each=packet=is=forwarded=to=the=appropri
ate=output=port
What=does=the=switching=fabric=do?=-=ans-
✔✔Moves=packets=from=input=to=output=ports.=3=Types:=memory,=bus,=and=crossbar
What=do=the=output=ports=do?=-=ans-
✔✔Receive=and=queue=the=packets=that=come=from=the=switching=fabric=and=send=the
m=over=to=the=outgoing=link
Routers=control=plane=functions=-=ans-
✔✔implements=routing=protocols,=maintains=the=routing=tables,=computers=the=forward
ing=table
Router=Lookup=(Task=1=of=6)=-=ans-
✔✔When=a=packet=arrives,=router=looks=at=the=destination=IP=address=and=determines
=the=output=link=by=looking=at=the=forwarding=table=or=FIB.
Router=Switching=(Task=2=of=6)=-=ans-
✔✔After=lookup,=the=switching=system=takes=over=to=transfer=the=packet=from=the=inpu
t=link=to=the=output=link
, Router=Queueing=(Task=3=of=6)=-=ans-
✔✔After=switching,=it=will=need=to=be=queued=if=the=link=is=congested.=The=queue=may
be=simple=as=FIFO=or=some=other=algorithm
Router=Header=validation=and=checksum=(4=of=6)=-=ans-
✔✔The=router=checks=the=packet's=version=number,=decrements=the=time-to-
live=field,=and=recalculates=the=header=checksum
Router=Processing=(Task=5=of=6)=-=ans-
✔✔The=routers=build=their=forwarding=tables=using=routing=protocols=such=as=RIP,=OS
PF,=BGP=-=they=are=implemented=in=the=routing=processors
Protocol=Processing=(Task=6=of=6)=-=ans-
✔✔The=routers,=in=order=to=implement=their=functions,=need=to=implement=the=followin
g=protocols:
-
Simple=Network=Management=Protocol=which=provides=counters=for=remote=inspection
-TCP=and=UDP=for=remote=communication=with=the=router
-Internet=Control=Message=Protocol=for=sending=error=messages
Switching=via=memory=-=ans-
✔✔The=ports=operate=as=I/
O=devices=in=an=operating=system.=When=an=input=port=receives=a=packet,=it=sends=an
=interrupt=to=the=routing=processor=and=the=packet=is=coped=to=the=processors=memor
y.=Process=extracts=address=and=looks=to=table=to=find=output=port.=Then=its=copied=to
=the=output=port=buffer
Switching=via=bus=-=ans-
✔✔When=input=receives=a=packet,=it=puts=an=internal=header=that=designates=the=outp
ut=port,=and=sends=it=to=a=shared=bus.=All=output=ports=will=receive=the=packet,=but=onl
y=the=designated=one=will=keep=it.=Speed=of=the=bus=limits=the=speed=of=the=router.
Switching=via=Interconnection=network=-=ans-
✔✔Interconnect=network=that=connects=N=input=ports=to=N=output=ports=using=2N=buse
s.=Can=carry=multiple=packets=at=a=time
Bandwidth=and=Internet=population=scaling=(problem=1=of=2=that=routers=face)=-=ans-
✔✔Caused=by:
1.=Increasing=number=of=devices
2.=increasing=volumes=of=network=traffic=due=to=new=applications
3.=new=technologies=such=as=optical=links=that=can=accommodate=higher=volumes=of=tr
affic
Services=at=high=speeds=(problem=2=of=2=that=routers=face)=-=ans-
✔✔New=applications=require=services=such=as=protection=against=delays=during=conge
stion,=and=protection=during=attacks=or=failures.
