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ECE544: Communication

Networks-II, Spring 2015

D. Raychaudhuri & D.

Reininger

Lecture 4

Includes teaching materials from L. Peterson

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Toda!s "ecture

• IP basics

– Service model, ac!et synta"

– IP address structure

– #RP, D$%P

– IP ac!et or'arding

• Routing rinciles

– (ellman)*ord algorithm & distance vector+RIP

– Di-!stra algorithm and lin! state +SP*

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I# $asics

(est /0ort Service 1odel

2lobal #ddressing Scheme

#RP & D$%P

IP Pac!et or'arding

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I# Internet

• %oncatenation o 3et'or!s

• Protocol Stac!

R2

R1

H4

H5

H3H2H1

Network 2 (Ethernet)

Network 1 (Ethernet)

H6

Network 3 (FDDI)

Network 4(point-to-point)

H7 R3 H8

R1

ETH FDDI

IPIP

ETH

TP R2

FDDI PPP

IP

R3

PPP ETH

IP

H1

IP

ETH

TP

H8

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Ser%ice &ode'! onne"tion#e$$ (%&t&'r&-&$e%)! *e$t-e++ort %e#i,er (.nre#i&#e $er,i"e)

/ p&"ket$ &re #o$t / p&"ket$ &re %e#i,ere% o.t o+ or%er

/ %.p#i"&te "opie$ o+ & p&"ket &re %e#i,ere% / p&"ket$ "&n e %e#&e% +or & #on' tie

! D&t&'r& +or&t 0er$ion Hen T en'thI%ent F#&'$ ++$et

TT Proto"o# he"k$.

o.r"e%%r

De$tin&tion%%r

ption$ (,&ri&#e) P&%(,&ri&#e)

4 8 16 1 31

D&t&

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(ragmentation and

)eassem*'• /ach net'or! has some 15• Strategy

– ragment 'hen necessary +15 6 Datagram

– try to avoid ragmentation at source host– re)ragmentation is ossible– ragments are sel)contained datagrams– use %S)PD5 +not cells or #1– delay reassembly until destination host

– do not recover rom lost ragments

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E+amp'e

H1 R1 R2 R3 H8

ETH IP (14) FDDI IP (14) PPP IP (512)

PPP IP (376)

PPP IP (512)

ETH IP (512)

ETH IP (376)

ETH IP (512)

I%ent ++$et

t&rt o+ he&%er

Re$t o+ he&%er

14 %&t& te$

I%ent ++$et

t&rt o+ he&%er

1

Re$t o+ he&%er

512 %&t& te$

I%ent ++$et 512

t&rt o+ he&%er

1

Re$t o+ he&%er

512 %&t& te$

I%ent ++$et 124

t&rt o+ he&%er

Re$t o+ he&%er

376 %&t& te$

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'o*a' ddresses

• Proerties– globally uni7ue

– hierarchical8 net'or! 9 host

• Dot 3otation– :;..?@.

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.atagram (orwarding• Strategy

– every datagram contains destinationBs address– i directly connected to destination net'or!, then or'ard to

host– i not directly connected to destination net'or!, then

or'ard to some router– or'arding table mas net'or! number into ne"t ho

– each host has a deault router– each router maintains a or'arding table

• /"amle +R= 3et'or! 3umber 3e"t $o : R<

= R:

< interace :

4 interace ;

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ddress Trans'ation• 1a IP addresses into hysical addresses

– destination host

– ne"t ho router

• echni7ues– encode hysical address in host art o IP address

– table)based

• #RP– table o IP to hysical address bindings

– broadcast re7uest i IP address not in table

– target machine resonds 'ith its hysical address– table entries are discarded i not rereshed

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)# .etai's

• Re7uest *ormat– $ard'areye8 tye o hysical net'or! +e.g., /thernet

– Protocolye8 tye o higher layer rotocol +e.g., IP

– $L/3 & PL/38 length o hysical and rotocol addresses

– eration8 re7uest or resonse– SourceCarget)PhysicalCProtocol addresses

• 3otes– table entries timeout in about :; minutes

– udate table 'ith source 'hen you are the target

– udate table i already have an entry– do not reresh table entries uon reerence

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)# #acket (ormat

T&r'etH&r%w&re%%r (te$ 2 / 5)

T&r'etProto"o#%%r (te$ / 3)

o.r"eProto"o#%%r (te$ 2 / 3)

H&r%w&re tpe 1 Proto"o#Tpe 8

o.r"eH&r%w&re%%r (te$ 4 / 5)

T&r'etH&r%w&re%%r (te$ / 1)

o.r"eProto"o#%%r (te$ / 1)

Hen 48 Pen 32 per&tion

o.r"eH&r%w&re%%r (te$ / 3)

8 16 31

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T& )#

H2

R

H1

I 1

I 12

T: network

1;;;2

1;;;112;;;3

12;;;5

• #1 #RP or maing IP6)#1 addr– medium is not a broadcast tye unli!e /thernet

– re7uires servers 'hich maintain #RP tables

– concet o multile Elogical IP subnetsF +LIS

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.namic /ost Contro'

#rotoco' ./C#• D$%P server er net'or! or IPaddress assignment

• Static list o IP6)hysical addr ordynamic binding rom common ool

• $ost boot)u via 'ell)!no'n address=GG.=GG.=GG.=GG

• D$%P Erelay agentF can be used toavoid one server er net'or!

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.namic /ost Contro'

#rotoco' ./C#• D$%P ac!et ormat +runs over5DP

Operation HType HLen Hops

Xid

Secs Flag

ciaddr

yiaddr

siaddr

giaddr

chaddr (1!"

....

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Internet Contro' &essage

#rotoco' IC• /cho +ing• Redirect +rom router to source host

• Destination unreachable +rotocol, ort, or

host• L e"ceeded +so datagrams donBt cycle

orever

• %hec!sum ailed

• Reassembly ailed

• %annot ragment

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)outing $asics

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)outing #ro*'em• 3et'or! as a 2rah

Problem8 *ind lo'est cost ath bet'een t'onodes

• *actors

– static8 toology– dynamic8 load

4

36

21

1

1

D

FE

*

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Two main approaces• DH8 Distance)vector rotocols

• LS8 Lin! state rotocols

• Hariations o above methods alied to8– Intra)domain routing +smallCmed net'or!s•RIP, SP*

– Inter)domain routing +largeCglobal

net'or!s•(2P)4

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.istance 3ector #rotoco's

• /mloyed in the early #ranet

• Distributed ne"t ho comutation

– adative

• 5nit o inormation e"change

– vector o distances to destinations

• Distributed (ellman)*ord #lgorithm

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.istance 3ector

• /ach node maintains a set o triles– (Destination, Cost, NextHop)

• /"change udates directly connected neighbors– eriodically +on the order o several seconds– 'henever table changes +called triggered udate

• /ach udate is a list o airs8– +Destination, Cost)

• 5date local table i receive a EbetterF route– smaller cost

– came rom ne"t)ho• Reresh e"isting routes delete i they time out

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.istri*uted $e''man-(ordStart Conditions:

Each router starts with a vector of (zero) distancesto all directly attached networks

Send step:

Each router advertises its current vector to allneighboring routers.

Receive step:pon receiving vectors fro! each of its neighbors"router co!putes its own distance to each neighbor.#hen" for every network $" router finds that neighbor

who is closer to $ than to any other neighbor.Router updates its cost to $. %fter doing thisfor all $" router goes to send step.

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E+amp'e - initia' distances

%

&

E

C

'

nfo at

node%

&

C

'

% & C

* +

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

+

+-

E , + -

,

+

-

E

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E recei%es .!s routes

%

&

E

C

'

nfo at

node%

&

C

'

% & C

* +

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

+

+-

E , + -

,

+

-

E

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E updates cost to C

%

&

E

C

'

nfo at

node%

&

C

'

% & C

* +

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

+

+-

E , / -

,

+

-

E

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recei%es $!s routes

%

&

E

C

'

nfo at

node%

&

C

'

% & C

* +

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

+

+-

E , / -

,

+

-

E

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updates cost to C

%

&

E

C

'

nfo at

node%

&

C

'

% & C

*

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

+

+-

E , / -

,

+

-

E

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recei%es E!s routes

%

&

E

C

'

nfo at

node%

&

C

'

% & C

*

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

+

+-

E , / -

,

+

-

E

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updates cost to C and .

%

&

E

C

'

nfo at

node%

&

C

'

% & C

* 0

* ,+ ,

+ + -

*

,

,

-

-

'istance to node

'

1

+-

E , / -

,

+

-

E

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(ina' distances

%

& C

'

nfo at

node%

&

C

'

% & C

2 0

2 ,0 ,

1 1 -

*

,

,

-

-

'istance to node

'

1

1-

E , 0 / -

,

0/

-

E

E

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(ina' distances ater 'ink

ai'ure

%

& C

'

nfo at

node%

&

C

'

% & C

*

* ,

,

, 1 -

*

,

,

-

-

'istance to node

'

,

1

-

E , 3 ,,

,

3

,,

E

E

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3iew rom a node

%

&

E

C

'

dest

%

&

C

'

% & '

, ,/ 0

* 02 3 /

/ ,, -

*

,

,

-

-

4e5t hop

E6s routing table

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.istance 3ector E+amp'e

#1 #$

#%

#& #'

%

$

%1

Inoat

3ode

R: R= R< R4 RG

R: ; 4 ) ) )

R= 4 ; = 4 )

R< ) = ; : ?

R4 ) 4 : ; )

RG ) ) ? ) ;

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.3 E+amp'e cont

#1 #$

#%

#& #'

%

$

%1

Inoat

3ode

R: R= R< R4 RG

R: ; 4 @ > )

R= 4 ; = < ::

R< @ = ; : ?

R4 > < : ; :;

RG ) :: ? :; ;

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.3 E+amp'e cont

#1 #$

#%

#& #'

%

$

%1

Inoat

3ode

R: R= R< R4 RG

R: ; 4 @ A :G

R= 4 ; = < ::

R< @ = ; : ?

R4 A < : ; :;

RG :G :: ? :; ;

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.3 E+amp'e 6 ater 'ink )2-)7 *reaks

#1 #$

#%

#& #'

%

%1

Inoat

3ode

R: R= R< R4 RG

R: ; 4 @ A :G

R= 4 ; ) < ::

R< @ ) ; : ?

R4 A < : ; :;

RG :G :: ? :; ;

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#1 #$

#%

#& #'

%

%1

Inoat

3ode

R: R= R< R4 RG

R: ; 4 ) ) )

R= 4 ; G 4 :4

R< ) ) ; : ?

R4 ) 4 : ; :;

RG ) :4 ? :; ;

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#1 #$

#%

#& #'

%

%1

Inoat

3ode

R: R= R< R4 RG

R: ; 4 ? > :>

R= 4 ; G 4 :4

R< ? G ; : ?

R4 > 4 : ; :;

RG :> :4 ? :; ;

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Te *ouncing eect

%

-0

,

,

&

C

&

C -,

dest cost

%C ,

,

dest cost

%

& ,-

dest cost

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C sends routes to $

%

-0 ,

&

C

&

C -,

dest cost

%C ,

+

dest cost

%

& ,-

dest cost

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$ updates distance to

%

-0 ,

&

C

&

C -,

dest cost

%C ,

1

dest cost

%

& ,-

dest cost

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$ sends routes to C

%

-0 ,

&

C

&

C -,

dest cost

%C ,

1

dest cost

%

& ,/

dest cost

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C sends routes to $

%

-0 ,

&

C

&C -

,

dest cost

%C ,

0

dest cost

%

& ,/

dest cost

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/ow are tese 'oops caused8

• bservation :8

– (Bs metric increases

• bservation =8– % ic!s ( as ne"t ho to #

– (ut, the imlicit ath rom % to #

includes itselJ

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%oiding te $ouncing

Eect• Select loo)ree aths

• ne 'ay o doing this8

– each route advertisement carriesentire ath

– i a router sees itsel in ath, it re-ects

the route• (2P does it this 'ay

– Sace roortional to diameterCheng" Riley et al

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Computing Imp'icit #ats

• o reduce the sace re7uirements

– roagate or each destination not only thecost but also its redecessor

– can recursively comute the ath

– sace re7uirements indeendent o diameter

5 y z

w u

v v uu w

w z

z y

y z

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.istance 3ector in #ractice

• RIP and RIP=

– uses slit)horiKonCoison reverse

• (2PCIDRP– roagates entire ath

– ath also used or e0ecting olicies

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)I# #acket (ormat

)ommand* +er ,eros

-et 1 Family -et 1 ddr

-et 1 ddr (cont."

/istance to -et 1

/istance to -et $

-et $ Family -et $ ddr

00

(net addr* distance pairs"

pdates sent 2&3 sec

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"ink State )outing

• /ach node assumed to !no' stateo lin!s to its neighbors

• Ste :8 /ach node broadcasts itsstate to all other nodes

• Ste =8 /ach node locally

comutes shortest aths to allother nodes rom global state

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"ink State )outing: $ui'ding

*'ocks• Reliable broadcast mechanism

– ooding

– se7uence number issues

• Shortest ath tree +SP algorithm

– Di-!straBs SP algorithm

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"ink state packets "S#s

• Periodically, each node creates aLin! state ac!et containing8

– 3ode ID– List o neighbors and lin! cost

– Se7uence number

– ime to live +L• 3ode oututs LSP on all its lin!s

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)e'ia*'e 'ooding• Mhen node i receives LSP rom node -8

– I LSP is the most recent LSP rom - that ihas seen so ar, i saves it in databaseand or'ards a coy on all lin!s e"cetlin! LSP 'as received on.

– ther'ise, discard LSP.

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S#T a'goritm .i9kstra

• SP N Oa

• or all nodes v – i v ad-acent to a then D(v) N cost +a, v

– else D(v) = infnity

• Loo– fnd w not in SP, 'here D(w) is min

– add w in SP

– or all v ad-acent to w and not in SP• D(v) = min (D(v), D(w) + C(w, v))

• until all nodes are in SP

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"ink State 'goritm

7looding:,) 8eriodically distribute link9stateadvertise!ent (S%) to neighbors

9 S% contains delays to each

neighbor-) nstall received S% in S database1) Re9distribute S% to all neighbors

8ath Co!putation,) se 'i;kstra6s shortest path algorith!

to co!pute distances to all destinations-) nstall

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(orward Searc 'goritm

.i9kstra:. InitialiKe Confrmed list 'ith sel entry ;=. *or node -ust added to confrmed list, call it EnextF

and select is LSP

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.i9kstra;S#( &etod 1

#1 #$

#%

#& #'

%

$

%1

Ste %onQrmed+R, cost, ne"tho

entative+R, cost, ne"tho

: +R:,;,) )

= +R:,;,) +R=,4,R=

< +R:,;,)

+R=,4,R=

+R,R=

.i9k t ;S#( & t d 1

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#1 #$

#%

#& #'

%

$

%1



4 +R:,;,)

+R=,4,R=

+R,R=

+R4,A,R

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#1 #$

#%

#& #'

%

$

%1



@ +R:,;,)

+R=,4,R=

+R

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.i9kstra S#T &etod 2

F

!

/ 4

)$

$

$

&

1

1

1

&

'

$tep PT D()< P() D(")< P(") D(%)< P(%) D(e)< P(e) D(+)< P(+)

2< 5< 1< = =

'

! ) / 4 F

.i9kst S#T & t d 2

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F

!

/ 4

)$

$

$

&

1

1

1

&

'


2< 5< 1< = =

1 D 2< 4< D 2< D =

'

! ) / 4 F


.i9kst S#T & t d 2

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F

!

/ 4

)$

$

$

&

1

1

1

&

'


2< 5< 1< = =

1 D 2< 4< D 2< D =

2 DE 2< 3< E 4< E

'

! ) / 4 F


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F

!

/ 4

)$

$

$

&

1

1

1

&

'


2< 5< 1< = =

1 D 2< 4< D 2< D =

2 DE 2< 3< E 4< E3 DE* 3< E 4< E

'

! ) / 4 F


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F

!

/ 4

)$

$

$

&

1

1

1

&

'


2< 5< 1< = =

1 D 2< 4< D 2< D =

2 DE 2< 3< E 4< E

3 DE* 3< E 4< E

4 DE* 4< E

'

! ) / 4 F



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F

!

/ 4

)$

$

$

&

1

1

1

&

'


2< 5< 1< = =

1 D 2< 4< D 2< D =

2 DE 2< 3< E 4< E

3 DE* 3< E 4< E

4 DE* 4< E

5 DE*F

'

! ) / 4 F


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"ink State in #ractice

• SP* +en Shortest Path *irstProtocol

– most commonly used routing rotocolin the Internet

– suort or authentication, addlhierarchy, load balancing

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;S#( #ackets 'e ption$ Tpe1

F#&'$ N.er o+ #ink$

ink tpe N.>T :etri"

ink $t&te ID

%,erti$in' ro.ter

$e?.en"e n.er

ink ID

ink %&t&

ption T in+or&tion:ore #ink$

"he"k$. en'th

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"ink State Caracteristics

• Mith consistent LSD(s, all nodes

comute consistent loo)ree aths• Limited by Di-!stra comutation

overhead, sace re7uirements

• %an still have transient loos

%

&

C

'

,1

0 -

,

Pac5et from )67

may loop around !/)

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;S#( Se

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#ro*'em: )outer (ai'ure

• # ailed router and comes u butdoes not remember the last

se7uence number it used beore itcrashed

• 3e' LSPs may be ignored i they

have lo'er se7uence number

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;ne so'ution: "S# ging

• 3odes eriodically decrement age+L o stored LSPs

• LSPs e"ire 'hen L reaches ;– LSP is re)ooded once L N ;

• Rebooted router 'aits until all LSPs

have e"ired• rade)o0 bet'een re7uency o LSPs

and router 'ait ater reboot

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Toda!s /omework• Peterson & Davie

) 4.:

ece544lec4_15.ppt

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