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Teaching C om puter Networking U sing Open Sou rce SoftwareDanie l Ne lson and Yau Man Ng

School o f Communicat ions and In format icsV ic tor ia Un ivers i ty o f Techno logy

Melbourne , Austra l ia{ d a n , y m a n } @ c a b s a v . v u . ed u . a u

1 A b s t ra c tF o r t h e p as t s ev en y ear s we h av e t au g h t a su b j ec t en t i t l edN e t w o r k S o f tw a r e a n d M a n a g e m e n t ( N S M ) f o r b o thco mp u te r sc i en ce an d e l ec t r i ca l en g in eer in g s t u d en t s . Wed i scu ss t h e ev o lu t i o n o f t h is su b j ec t sy l l ab us i n r esp o n se t oth e ch an g in g r eq u i r emen t s o f th e wo rk p l ace en v i ro n men t ,e v e r i m p r o v in g t e c h n o l o g y a n d t h e n e e d t o c o m b i n e t h e o r yan d p rac t i ce i n t each in g su b j ec t s su ch as t h i s . We u sedo p en so u rce so f twa re ex c lu s iv e ly i n o u r l ab o ra to ryex erc i ses an d we p ro v id e t h e r a t i o n a l e b eh in d o u r ch o i ce o fsp ec i f i c so f tware p ack ag es .2 Int roduct ionNS M was f i r s t i n t ro d u ced i n 1 9 9 3 i n r esp o n se t o t h ep erce iv ed n eed fo r g r ad u a t es wh o a re t r a i n ed i n t h ein t eg ra t io n an d ad m in i s t ra t i o n o f co m p u te r n e two rk s .Oth er s v o i ced s imi l a r co n cern s [1 3 ] . By n a tu re an dt rad i t ion , ter t iary ins t i tu t ions in Aust ral ia have s t ructuredth e i r co u r ses to ed u c a t e i n t h e g en e ra l r a t h e r t h an t r a i n fo rt h e sp ec i f i c . Th i s p o l i cy , i n man y r esp ec t s , h as p l acedg rad u a t es a t a d i sad v an t ag e wh en c o mp e t in g fo r j o b s . I tmu s t b e emp h as i sed t h a t a t e r t i a ry d eg ree i s n o l o n g er at i ck e t to a j o b , b u t a p r e r eq u i s i t e fo r a g o o d j o b .

T h e c h a l l e n g e i s - h o w d o w e m a k e o u r c o u r s e( t each in g meth o d s , l ab o ra to ry mate r i a l an d t ech n o lo g i es )r e l ev an t t o th e n eed s o f i n d u s t ry wh i l e main t a in in g aco mmi tmen t t o so u n d p ed ag o g i ca l p r ac t i ce , a s we l l a sap p ea l i n g t o a b ro ad c ro ss sec t i o n o f s t u d en t s?3 Sy l l a b usNS M i s a fo u r -h o u r su b j ec t co n s is t i n g o f two h o u r s o fl ec tu res an d two h o u r s o f su p erv i sed p rac t i ca l wo rk p e rweek . Th i s su b j ec t i s o n e o f t h r ee t h a t we o f f e r i n co mp u te r

Permiss ion to make d igi ta l or hard copies o f e l l o r p e r t o f t h i s w or k f o rpe r s onal o r c l a s sr oom us e is g r an t e d w i t hou t f e e p r ov i d e d t h a tc op i e s a r e no t m a d e o r d i s t r i b u t e d f o r p r o f i t o r c om m e r c i a l a d v a n -t a ge a nd t h a t c op i e s b e a r t h i s no t i c e e nd t he f u l l c i t a t i on on t he f i r st pa ge .To c opy o t he r w i s e , t o r e pub l is h , t o pos t on s e r v e rs o r t ored is tr ibute to l is ts , requires pr ior spec i f ic permiss ion and /or a f e e .I T i C S E 2 0 0 0 7 / 0 0 H e l s in k i , F i n la n d 2 0 0 0 A C M 1 - 5 8 1 1 3 2 0 7 - 7 / 0 0 / 0 0 0 7 . .. $ 5 . 0 0

n e two rk in g ( as d i s t i n c t f ro m d a t a co mm u n ica t i o n s ) . I t is t h eth i rd su b j ec t o f t h e seq u en ce , w i th t h e f i r s t su b j ec t r a t h e ri n ap p ro p r i a t e ly en t i t l ed Da t a Co m mu n ica t i o n s , an d t h es e c o n d e n t i tl e d N e t w o r k O p e r a t in g S y s t e m s ( N O S )A d m i n i s t r a t i o n ( w h i c h c o n c e n t r a t e s e n t i r e l y o n W i n d o w sNT V.4 ad min i s t r a t i o n ) . Ev en wi th t h r ee su b j ec t s d ev o t edt o c o m p u t e r n e tw o r k i n g , w e f m d t h a t m a n y w o r t hw h i l eto p i cs may n o t b e i n c lu d ed o r co v e red t o th e d es i r ed d ep th .Th e a ims o f t h e su b j ec t a r e t o en ab l e g rad u a t es to : Un d er s t an d t h e cap ab i l i ti e s , l imi t a t io n s an d cu r r en t

d e v e l o p m e n t s i n c o m p u t e r n e t w o r k i n g,* Ad ap t t o ch an g es i n n e two rk in g h ard wa re an d /o rso f tware t ech n o lo g y , P r e p a r e f o r a p r o f e s s io n a l c ~ e e r i n c o m p u t e r

n e two rk in g , an d P rep are fo r p o ss ib l e s t u d y a t a g r ad u a t e l ev e l .

C o m p u t e r n e t w o r k s a n d d a t a c o m m u n i c a t i o n s a r e n o wwel l e s t ab l i sh ed an d matu re a r eas o f s tu d y . We s t ro n g lyb e l i ev e t h a t we a r e p ed ag o g i ca l l y o b l i g a t ed t o co n cen t r a t eo n en d u r in g t h eo re t i ca l co n cep t s , an d n o t n ecessa r i l y t h eimp era t i v es o f t h e w o rk fo rce . I n s t ru c to r s a r e o f t en t o mb etween t each in g t h eo re t i ca l f u n d amen ta l s an d t h e n eed t oin c lu d e s t a te o f t h e a r t co n ce p t s an d p rac t i ca l i n fo rma t io nth a t s tu d en t s can u se t o en h a n ce t h e i r mark e t ab i l i ty . We a remin d fu l o f t h e t r an s i en t n a tu re o f sp ec i f i c n e two rk t r a i n in g :fo r ex amp le , i n t h e ea r l y 1 9 9 0 ' s , No v e l l was t h e d o min an tp l ay er i n n e two rk in g o p era t i n g sy s t ems , b u t n o w h as b eenred u c ed t o b e in g a r e l a t i v e ly min o r p l ay er i n t h i s a r ea .Wh i l s t s ev era l o th e r u n iv er s i t i e s a l so t ak e t h e p rac t i ca lWin d o ws N T ad m in i s t r a ti o n ap p ro ach [4 ] , we f ee l t h a tm o r e i s r e q u ir e d f r o m a w e l l - ro u n d e d c o m p u t e r n e tw o r k i n gp ro fess io n a l .

T h e t e x t b o o k p r e s c r ib e d f o r N S M i s ComputerNetworks, b y Tan en b au m [1 2 ] . P r i o r t o 1 9 9 6 , t h ep resc r i b ed t ex t was b y Hal sa l l [ 6 ] . We b e l i ev e t h a t t h es t r es s o n TCP / IP p ro to co l s an d t h e Tan en b au m's r e l a t i v e lyo p in io n a t ed d i sco u r se mak es i n t e r es t i n g r ead in g fo r t h eav erag e s t u d en t . Th eo ry fo r t h i s su b j ec t co v er s :In t ro d u c t i o n , Ap p l i ca t i o n Lay er , T ran sp o r t Lay er , Ne two rkL a y e r a n d t h e M e d i u m A c c e s s L a y e r . T h i s o r d e r in g d i f fe r sf ro m th e t ex t , in t h a t we cu r r e n t l y ap p ly a t o p d o w na p p r o a c h , r a t h e r t h a n t h e b o t t o m u p a p p r o a c h u s e d b yT a n e n b a u m . T h e r e a s o n f o r t h is c h a n g e w a s t o t e a c h w h a t

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s tudents consider more in teres t ing top ics (e .g . app l icat ions)ea r l y an d t o en su re t h a t ad eq u a t e t ime i s sp en t o n t h e t o pl a y e rs o f t h e r e f e r e n c e m o d e l .

Ov e r t h e sev en -y ea r t ime sp an t h a t we h a v e t au g h t t h issu b j ec t , emp h as i s h as sh i f t ed f ro m co n cen t r a t i n g a lmo s tco m p le t e ly o n t h e l o wer l ay er s ( t r an sp o r t an d b e lo w) i n t h eear l i e r y ea r s t o t h e cu r r en t a l l o ca t i o n o f a t l eas t o n e- th i rd o ft h e t ime t o t h e ap p l i ca t i o n l ay er , wh ere t h e re i s a g r ea t d ea lm o r e p r o g r a m m i n g a n d m a n a g e m e n t a c t i v it y .4 La b o r a t o r i e sTh e su b j ec t co n s i s ts o f f i v e l ab o ra to ry ex p er imen t s an d o n eass ig n men t i n a t h i r t een week semes t e r . Each ex p er imen tg o es fo r two w eek s an d r eq u i r es a fo rm al p rac t i ca l r ep o r tan d d em o n s t r a t i o n . Th e o b j ec t i v es a r e : To ex p o se t h e s t u d en ts t o cu r r en t d ev e lo p m en t an dp rac t i ce i n co m p u te r n e two rk in g , To imp ro v e t h e s t u d en t s ' r e sea rch sk i ll s an d

co n f id en ce , an d To r eq u i r e s t u d en t s t o r ead an d p ro cess o n - l i n em a n u a l s , R e q u e s t F o r C o m m e n t d o c u m e n t s ( R F C s ),F r e q u e n t l y A s k e d Q u e s t i on s ( F A Q s ) , p r o d u c t

i n fo rmat io n , e t c .Be in g ab l e t o r ead an d u n d er s t an d t ech n i ca ld o cu men ta t i o n i s n o n - t r i v i a l an d r eq u i r es p rac t i ce an d i s ab as i c r eq u i r emen t o f an y fu tu re n e two rk ad min i s t r a to r an d ,i n d eed , an y co mp u t in g p ro fes s io n a l . To t h i s en d , d e t a i l edt ech n i ca l a s s i s t an ce i n t h e l ab o ra to ry g rad u a l l y d ecreasesd u r in g t h e semes t e r . I n i t i a l l y , co mp reh en s iv e s t ep -b y - s t epin s t ru c t i o n s a r e g iv en i n o rd er t o acco mp l i sh a l ab o ra to ry .As t ime p asses , l e s s p r ec i se i n s t ru c t i o n i s g iv en , an d t h es tu d en t is r eq u i r ed t o b eco me m o re i n d ep en d en t i n o rd er t osu ccess fu l l y co mp le t e t h e p rac t i ca l.

L a b o r a t o r y w o r k i s o f t e n t im e c o n s u m i n g f o r b o t hs tu d en t s an d t u to r s . Gen era l l y , s t u d en t s wo rk i n g ro u p s o ftwo . F ro m o u r ex p er i en ce , an d t h a t o f o th e r s [2 ,5 ] , g ro u pd y n amics imp ro v e l ea rn in g o u t co mes wh en s t u d en t s wo rkt o g e t h e r b y m a k i n g t h e s u b j e c t m o r e e n j o y a b l e a n din teres t ing . For most s tuden ts , th is i s the f i rs t t ime that theyh av e fu l l ad min i s t r a t i v e ri g h t s o n a Un ix sy s t em. As a ru l e ,mo s t s t u d en t s a r e n o t ab l e t o f i n i sh th e p rac t i ca l wo rk i n t h es c h e d u le d t i m e , a n d i n m a n y c a s e s t h e y n e e d t o c o m e b a c kin t h e i r o w n t ime . Of t en , wh e n s t u d en t s l a t e r r e t u rn ed , t h eyh av e fo u n d t h a t an o th er g ro u p h ad o v erwr i t t en t h e i r wo rk ,wh ich mean t t h a t t h e i r ea r l i e r co mp le t ed wo rk h ad t o b erep ea t ed . I t i s o f t en t h e case t h a t a s t u d en t acco mp l i sh es t h et ask o n a su b seq u en t a t t emp t f a r mo re k n o wled g eab ly an deff icien t ly .5 La b o r a t o r y Fa c i l i ti e sThe network laboratory cur rent ly consists of o lderco mp u te r s r e t i r ed f ro m o th er l ab o ra to r i es , each f i t t ed wi thtwo E th ern e t ca rd s . I t may ac tu a l l y b e b e t t e r t o u se o ld e rmach in es ( as l o n g as t h ey a r e r e l i ab l e ) , b ecau se s t u d en t sd o n ' t h av e t o wo r ry ab o u t ' b r eak in g ' an y th in g , an d s t a f f

n e e d n o t w o r r y a b o u t t h e l o s s o f v a l u a b le c o m p o n e n t s . W en o te t h a t t h i s l e s s t h an o p t imal se tu p i s n o t u n iq u e t o o u ru n iv er s i t y [8 ] . Th e P Cs a r e co n n ec t ed t o t h e Un iv er s i t yn e tw o rk t h ro u g h a L in u x -b ase d f i r ewal l. Th i s f i r ewal l i s toco n t a in t h e n e two rk t r a f f i c wi th in t h e l ab o ra to ry an d p ro t ec tt h e u n iv er s i t y n e tw o rk f ro m th e s t u d en t s .

Eq u ip m en t -wi se , NS M i s r e l a t i v e ly ch eap t o ru n . Th esu b j ec t , h o wev er , h as h i s t o r i ca l l y r eq u i r ed an ex c lu s iv eco m p u te r l ab o ra to ry . Lec tu re r s o f o th e r su b j ec t s sh a r i n g t h esame l ab o ra to ry fo u n d i t imp o ss ib l e t o d e p en d o n t h eav a i l ab i li t y o f t h e i r so f tware . Of t en , m ach in es were l e f t insu ch a s t a t e t h a t l a t e r s t u d en t s co u ld n o t u se t h em. Weo v e r c a m e t h is p r o b l e m b y i n t ro d u c i n g t w o m o b i l e r a c ks f o reach co mp u te r , a l l o win g a h a rd d i sk t o b e eas i l y ex ch an g e dwi th an o th er co n t a in in g t h e r eq u i r ed so f tware p r i o r t o t h en ex t p rac t i ca l . NS M u sed t h e l ab fo r two d ay s a week . Atech n i c i an se t u p each co mp u te r wi th t h e ap p ro p r i a t e h a rdd i sk p r i o r t o t h e n ex t d ay ' s l ab s . Th e mo b i l e r ackar r an g emen t a l so f ac i l i t a t ed s t u d en t s u s in g t h e i r o wn h ardd i sk . I n i t ia l l y , mo s t s t u d en t s o p t ed t o u se t h e p ro v id ed h ardd is k s, b u t b y t h e f o u r t h w e e k o f s e m e s t e r , e v e r y g r o u p h a dp u rch ased t h e i r o wn h a rd d i sk an d r ack . S tu d en t s fo u n d t h a tt h e m o b i l e r a c k s a l l o w e d t h e m t o i m m e r s e t h e m s e l v e s i nt h e n e w n e t w o r k i n g e n v i r o n m e n t , a s t h e y w e r e a b l e t o u s et h e s y s t e m a t h o m e . W e d i d n o t i m p l e m e n t t h e c o m m o n f i lesh ar in g tech n iq u e as su g g es t ed b y M ay o an d Kearn s [9 ], a ss t ud e n ts w a n t e d a c o m p l e t e s y s t e m t o w o r k o n a t h o m e .6 So f t w a r eTh e so f tware u sed i n o u r n e two rk in g l ab o ra to r i es i s o p enso u rce (p u b l i c d o main ) . OS S ex p o ses t h e s t u d en t t o t h eO p e n S o u r c e p h i l o s o p h y a nd d e v e l o p m e n t p a r a d ig m a n da l so p r o v i d e s a n e x a m p l e o f t h e w a y t h a t p e o p l e c a nco o p era t e o v er l a rg e d i s t an ces t o p ro d u ce p ro fes s io n a lq u a l i t y so f tware . Deb in a , Ok en an an d S to n e [3 ] g iv e ah i s t o ry an d r a t i o n a l e fo r OS S . Oth er s a rg u e ab o u t i t s f u tu rean d meth o d o lo g y [1 , 1 0, 1 1 ] . W e fmd , h o we v er , t h a t OS Si s i d ea l fo r o u r n e two rk in g en v i ro n men t . I t s h ig h q u a l i t yan d t h e f ac t t h a t i t is f r ee f ro m l i cen s in g d i f f i cu l t ie s g r ea t l yap p ea l s t o s t u d en t s wh o wan t t o u se i t a t h o me. Al so , OS Sex p o ses t h e so f tware mo re t o t h e u se r . Th ere a r e n ou n d o c u m e n t e d s y s t e m c a l l s a s s o m e t i m e s a r e f o u n d i nc o m m e r c i a l s o f t w a re .

T h e p r a c t i c a l e x e r c is e s c o m p l e t e d i n 1 9 9 9 w e r e b a s e do n t h e fo l l o win g so f tware p ack ag es : S l ack ware o r Re d Ha t d i s t r i b u t io n o f L in u x , A p a c h e W e b S e r v e r , P H P , a n d M y S Q L , S e c u r e s h e ll , P r e t t y G o o d P r i v a c y ( p g p ) , a n d s o f t w a r esecu r i t y u t i li t ie s (m d 5 su m , d ig i t a l ce r t i f ica t es ) , N e t w o r k D i a g n o s t ic u t il it i es ( a r p , p i n g , t r a c e r o u t e ,t c p d u m p ) ,

A r o u t e r b a s e d o n L i n u xT h e s e p r a c t i c a l e x p e r i m e n t sh t t p : / / m e l b a . v u . e d u . a u / - e e c 3 7 0 4 .

m a y b e f o u n d a t

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6.1 Linux Instal lationT h is l a b o ra to ry e x e rc i s e r e q u i re s s tu d e n t s t o in s t a l l a n dc o n f i g u r e t h e o p e r a t i n g s y s t e m s o f t w a r e f o r a U n i x / L i n u xw o r k s t a t i o n i n a n e t w o r k i n g e n v i r o n m e n t . I t w a s c h o s e n f o rth e fo l lo w in g r e a s o n s : S tu d e n t s h a v e h a d p r io r e x p o s u re to th e U n ix

e n v i r o n m e n t a s u s e rs . M o s t , h o w e v e r , p e r c e i v e d U n i xa s a rc a n e a n d d i f f i c u l t t o a d m in i s t e r . T h e r e m o v a l o fth i s p e rc e p t io n h e lp s to b u i ld th e i r s e l f - c o n f id e n c e inc o m p u t e r n e t w o r k i n g ,

A s s tu d e n t s u s e th e U n ix e n v i ro n m e n t fo r o th e rs u b je c t s th e i r w o rk in th e L in u x e n v i ro n m e n t g iv e st h e m a d d e d U n i x e x p e r i e n c e,

L i n u x h a s a r e l a t i v e ly l o w d e m a n d o n h a r d w a r ere s o u rc e s a n d i s a l so th e b a s i s fo r a l l o u r l a t e rl a b o ra to ry e x e rc i s e s . T h e c o m p le te s y s t e m a s in s t a l l e db y th e s tu d e n t s i n c lu d e d th e e x t r a p a c k a g e s o f S ta rO f f i c e a n d V i s u a l A g e J a v a ,

U n ix a d m in i s t r a t io n d i s t in g u i s h e s th e s tu d e n t f ro m th et y p i c a l s y s t e m a d m i n i s tr a t o r. U n i x a l o n g w i t hW i n d o w s N T A d m i n i s t r a t i o n p r o v i d e a u s e f u l r e s n m 6fo r fu tu re jo b h u n t in g .

6 .2 W e b S e rv e r , P H P an d M y S Q LT h e d r i v i n g f o r c e b e h i n d t h e e n o r m o u s g r o w t h o f I n t e r a c tt r a f f i c i n th e p a s t f e w y e a r s w a s th e r e s u l t o f t h ed e v e l o p m e n t o f w e b b r o w s e r c l i e n ts s u c h a s N e t s c a p e a n dIn te rn e t E x p lo re r a n d w e b s e rv e r s s u c h a s A p a c h e . S tu d e n t sa re f a m i l i a r w i th th e v a r io u s w e b c l i e n t s , b u t i t is im p o r t a n tth a t t h e y s h o u ld a l s o u n d e r s t a n d th e o p e ra t io n o f t h e w e bs e rv e r , w h ic h i s t h e fo u n d a t io n o f o n - l in e b u s in e s s .

A p a c h e i s c u r re n t l y th e m o s t p o p u l a r w e b s e r v e r an d i sa l s o o p e n s o u rc e . O n c e a g a in , s tu d e n t s a re r e q u i re d to r e a dt h r o u g h t h e d o c u m e n t a t i o n i n c l u d e d w i t h t h e p a c k a g e , a n da n y a d d i t io n a l i n f o r m a t i o n a v a i l a b l e f r o m t h e w e b , t ob e c o m e t h e W e b M a s t e r . V a r i o u s c o n f i g u r a ti o n s r e q u ir i n ga c c e s s c o n t ro l , p ro x y fo rw a rd in g a n d a s im p le o n - l in e s h o pf ro n t h a v e to b e im p le m e n te d in th i s e x e rc i se .

P H P i s a s e r v e r - s i d e H T M L - e m b e d d e d s c r i p t i n gl a n g u a g e t h a t al l o w s t h e p r o d u c t i o n o f d y n a m i c w e b p a g e s .M y S Q L i s m u l t i - us e r , m u l t i - th r e a d e d S Q L d a t a b a s e s e r ve r .T h i s t r i o o f o p e n s o u r c e p a c k a g e s d e m o n s t r a t e s t h e p o w e ro f c l i e n t - s e rv e r a p p l ic a t io n s . T h e y a l lo w th e s tu d e n t t oi r rq a l e m e n t a p ro to ty p e fo r a r e a l - l i f e e -c o m m e rc ea p p l i c a t io n .

S tu d e n t s f in d th i s p ra c t i c a l p a r t i c u la r ly c h a l l e n g in g , a sth e th re e p a c k a g e s r e q u i re c lo s e in t e g ra t io n fo r t h e s y s t e mt o w o r k p r o p e r l y . S t u d e n t s h a v e t o c o m p i l e f r o m s o u r c ec o d e. T h i s d e m a n d s a g o o d u n d e r s t a n d i n g o f U n i xc o m m a n d s a n d f i le s y s t e m l a y o u t , a s w e l l a s th e m a t u r i t ya n d p a t i e n c e to r e a d th ro u g h th e o n - l in e m a n u a l c a re fu l ly .6.3 Secure shel l , PG P, and Software In tegr i tyT h e i m p o r t a n c e o f n e t w o r k s e c u r i t y c a n n o t b eu n d e r e st i m a t e d. T h e i n c i de n c e s o f s t o l e n U n i x p a s s w o r d s

b y u s i n g n e t w o r k s n i f f i n g t o o l s i n a b r o a d c a s t n e t w o r k a r ec o m m o n in t e a ch i n g e n v i r o n m e n t s . T h e d a n g e r o f p o w e r f u ln e tw o rk d i a g n o s t i c t o o l s , s u c h a s tcpdurnp, fa l l ing in to thew r o n g h a n d s w a s d i s c u s s e d . T h e s e e x e r c i s e s w e r e c h o s e nfo r t h e fo l lo w in g r e a s o n s : T h e y d e m o n s t r a t e t h e u s a g e o f v a r i o u s e n c r y p t i o n

a l g o r i th m s d i s c u s s e d i n l e c tu r e s. T h e u s e o f o p e ns o u r c e s o f t w a r e s h o w s t h a t s e c u r i t y d o e s n o t d e p e n do n o b s c u r i ty ,

T h e y a l e r t s tu d e n t s t o th e c h a l l e n g e s o f n e tw o rks e c u r i ty a n d in t ro d u c e a v a i l a b le to o l s fo r t h ep r e v e n t i o n a n d m a n a g e m e n t o f s e c u r i t y b r e a c h es .

6.4 Netw ork Diagnost ic Ut i l i t iesA s u c c e s sf u l n e t w o r k m a n a g e r n e e d s t o o l s t o d i a g n o s em a n y p r o b l e m s t h a t a n e t w o r k m a y s u f f er . S o m e b a s i cn e t w o r k d ia g n o s t ic t o o l s ( p i n g , t r a c e r o u t e , t c p d u r n p a n dt i m e d o m a i n r e f l e c t o r m e t e r ( T D R M ) ) w e r e i n t r o d u c e d inth i s e x e rc i s e . S tu d e n t s a re r e q u i re d to d e lv e fu r th e r i n to th eo p e r a t i o ns o f p i n g a n d t r a c e r o u t e a n d r e a d t h e r e l e v a n tR F C o f th e p ro to c o l s u s e d in th e s e u t i li t i es . B e c a u s e o f al a c k o f e q u i p m e n t t h e u s e o f th e T D R M f o r p h y s i c a ln e t w o r k d i a g n o s is w a s c o n d u c t e d a s a d e m o n s t r a t io n o n l y .T c p d u m p w a s u s e d to e x a m i n e th e o p e ra t io n s o f A R P a n dtraceroute.6.5 Ro uter Insta l la tionT h e s u c c e s s o f n e tw o r k i n g c o m p a n i e s , s u c h a s C I S C O ,w h ic h s p e c ia l i s e s in ro u te r s a n d s w i t c h e s , a n d th e h ig hd e m a n d f o r I T p e r s o n n e l s k i l l e d i n t h e c o n f i g u r a t i o n a n da d m i n i s t ra t i o n o f r o u t e r s , d e m a n d t h e i n c l u s io n o f r o u t e rin s t a l l a t io n a n d u s a g e a s a l a b o ra to ry e x e rc i s e . A ro u te rb a s e d o n L i n u x m a y n o t m a t c h t h e p e r f o r m a n c e o fc o m m e rc ia l ro u te r s , b u t i t i s a d e q u a te to d e m o n s t ra t e t h ep r in c ip l e s a n d o p e ra t io n o f a ro u ter . In th i s e x e rc i s e ,s t u de n t s w o r k i n g r o u p s o f t w o o n t w o a d j a c en t P C s .S t u d e nt s p e r f o r m t h e n e c e s s a r y c o n f i g u r a ti o n t o m a k e o n eo f th e P C s in to a ro u te r a n d th e o th e r i n to a w o rk s t a t io nw i t h t h e n e c e s s a r y n e t w o r k a d d r e s s e s a n d r o u t i n g t a b l e .E a c h g r o u p p h y s i c a l l y c re a t e s a s u b n e t o f t h e ir o w n a n dm u s t b e a b l e t o c o m m u n i c a t e w i t h a n o t h e r g r o u p ' s s u b n e tv i a t h e c o m m o n s u b n e t c o n n e c t i n g t h e m . S t u d e n t s a r er e q u i r e d t o b e f a m i l i a r w i t h t h e u s a g e o f t h e f o l l o w i n gc o m m a n d s : r o u t e , n e t s t a t , i f c o n fi g , p i n g , a n d a r p .6 . 6 P ro g ra mm in g A s s ig n m e n tIn e a r l i e r y e a r s t h i s a s s ig n m e n t c e n t re d o n s im u la t io n s o fn e t w o r k i n g p r o t o c o l s . I t w a s s u c c e s s f u l i n e n h a n c i n g t h es t ud e n ts u n d e r s t a n d i n g o f n e t w o r k i n g p r o t o c o l s. F e e d b a c kf r o m s t u d e n ts a n d t h e d e m a n d f r o m i n d u s t r y n e c e s s it a t e dt h e c h a n g e t o s o c k e t p r o g r a m m i n g . P r o g r a m m i n g w i t hU n i x s o c k e t s g i v e s st u d e n ts e x p e r i e n c e w i t h p r o t o c o l s a n dc o m m u n i c a t i o n b e t w e e n p r o c e s s e s w i t h o u t h a v i n g t o d e a lw i th m a c h in e d e p e n d e n c ie s a t l o w e r l e v e l s. S tu d e n t se n c o u n t e r d i f f e r en t c h a l l e n g es i n t h is a s s i g n m e n t f r o m a n ye x p e r i e n c e d i n t h e i r p r e v i o u s p r o g r a m m i n g c l a s s e s .

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Students must consider race conditions, concurrentprocesses, mutual exclusion and other details of inter-process communication. Our students, who have had noprevious experience with socket programming, are givensamples of code to manage the socket in the assignment. Itstill remains a significant effort on the students' part tointegrate this sample code into the code required to do therequired task for both the server and client of theirapplication. Over the years, students have been asked toimplement several client-server applications such as simpleFTP client and server and a simple multi-user chat clientand server. Students may use any programming language todevelop the application, but, typically, Java is the languageof choice, as it is the easiest with which to developapplications for the Internet. The assignment wasconsidered very useful and has often enhanced theirchances of getting employment in the area. See below.7 S t u d e n t F e e d b a c kThe overall feedback from students regarding this subject ispositive. Typical responses have been: Students ranked the exercises and the programmingassignment as highly relevant and valuable, The theoretical parts of the subject are ranked as onlyaverage, Returning students have often remarked that thissubject was a very important part in securingemployment, as well as being an integral foundation ofknowledge required for their employment, As Linux has become more popular in the last twoyears, students' perception of the installation exercisehave changed from being neutral to quite positive, Students recognised early in the semester that a gapexisted in their Unix/programming background. Thiscoupled with the difficulty of the laboratory exercisesmeant that many acquired additional resource material

such as "Linux for Dummies".8 C o n c l u s i o n sNSM has changed a lot, both in theory and practical work,over the years that the subject has been in existence. Sevenyears ago we faithfully taught the ISO/OSI seven-layerreference model of networking. Today, we may still refer toOSI, but we now firrnly reside in the TCP/IP networkingcamp. Some things about the subject have not changedmuch, however. This subject has always required asignificant time commitment by students. Much of thework that they do is unsupervised and requires a matureproblem solving approach to be able to finish the task.Students initially aren't used to being required to workindependently, and often flounder when required to readand apply technical documentation. As the semesterprogresses, most improve dramatically.

Despite the time consuming requirement for supportand maintenance of the computer laboratory, it is veryrewarding to fred that students appreciate the extra work

that both they and we put into completing the subjectsuccessfully. The real payback for them comes whenapplying for employment in the networking area and notingthat their experience is highly valued by employers for theeducation and practical training that they have akeady had.Open Source Software allows students the freedom totake their software and all their development work betweenhome and university by means of a mobile rack. Thisallows greater exposure to the subject material and,consequently, improved learning outcomes.

R e f e r e n c e s[1] Bollinger, T., et. al., Open-Source Methods: PeeringThrough the Clutter, IEEE Sof tware, 16, 4,(July/August 1999), 8-11.[2] Daigle, R. J. and Niccolai, M. J., Inter-class Synergyby Design, ACM SIGCSE Bul le t in , 29, 1 (March1997), ACM Press, 92-95.[3] DiBona, C., Ockman, S., and Stone, M., Ed., OpenSources: Voices from the Open So urce Revolution,O'Reilly, 1999.[4] Elenbogen, B. S. Computer Network Management:

Theory and Practice, ACM SIGCSE Bul le t in , 31, 1,1999, ACM Press, 119-121.[5] Felder, R. M., Reaching the Second Tier - Learningand Teaching Styles in College Science Education,Journal o f College Science Teaching, 23, 5,(March/April 1993), 286-290.[6] Halsall, F. Data Com munications, ComputerNetworks and Open Sys tems, 4 th Edition, AddisonWesley, 1996.[7] Lankewicz, L. B. Resources for Teaching ComputerNetworks, ACM SIGCSE Bul le t in , 30, 1, (March1998), ACM Press, 112-116.[8] Levin, M., A Prototype for a Data CommunicationsLaboratory or A Data Comm Lab in a Closet, A C MSIGCSEBul le t in , 29, 1, 1997, 1 ACM Press, 79-183.

Mayo, J. and Kearns, P. A Secure NetworkedLaboratory for Kernel Programming, A C M S I G C SEBulletin, 30, 3, September 1998, ACM Press, 175-177.McConnell, S., Open-Source Methodology: Readyfor Prime Time?, IEE E Sof tware, 16, 4, (July/August1999), 6-7.O'Reilly, T., Lessons From Open-Source SoftwareDevelopment, Communicat ions o f the ACM , 42, 4,(April 1999), ACM Press, 33-37.Tanenbaum, A. S., Computer Networks, 3ra Edition,Prentice Hall, 1996.Tucker, A. B. and et. al., Strategic Directions inComputer Science Education, ACM Comput ingSurveys, 28, 4, (December 1996), ACM Press,836-845.

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