Why th e Internet on ly just works

BT T e ch no l o gy J ou r na l • V ol 24 No 3 • J ul y 20 06

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su rvive mo vi ng ne two rks, t her e is no cu rre nt co mp elling

sim ilar app licat ion for n orm al Int ernet user s. DHCP

serve s t hes e us ers w ell, w ith appl ica tion s su ch a s e- mai l

and in sta nt m es sa gin g s imp ly re co nn ectin g ea c h t ime

th e I P a ddr ess ch ang es.

It is pos s ibl e th at th e eme rge nce of pho ne- li ke

device s that support b oth 3G and IE EE802.11 ra dios will

cha nge t his sto ry. Ho weve r, th ere is st ill a ques ti on as t o

whe th er any ap p licat ions act ual ly ca re. I bel ieve th at

V oIP ma y b e t h e on e a pp licat io n t ha t ne ed s M obi le IP ,

but it is far f rom cl ear that m ob ile tel eph o ny oper at ors

will provi de the network su pport needed f or Mobile IP to

work, especially as this is in dir ect com petition w ith the ir

regu lar tel epho ne s ervic e.

Th e second reas on for a lack of de ploymen t is the

usual chicken -and-egg probl em. Why deploy Mo bile IP

for eign agen ts on you r netw or k to sup port vis iting hos ts

whe n those hosts d o n ot suppo rt Mo bile IP y et? And why

i nteg rat e M obi le I P into th e ho st st ack , w hen th ere i s no

netw ork suppor t yet ?

T h e l i ke l y s t o r y i s t h a t m o bi l i t y w i l l i n f a c t b e s o l v e d

at the la st m inu te a t la ye r 4 o r abo ve, rath er than lay er

3 . M ob ili ty e x te ns i on s to t ran spo r t pr o to c ol s a r e

compara tively easy to d eploy, requiri ng no support from

forei gn networks , an d so do not s uffer fr om the chicken -

and -egg pro bl em t o t he s am e ex ten t. Bu t t he rus h to

add mo bilit y supp ort wi ll li kely c ome at the last minut e ,

whe n a pp licat ion s t hat re ally ne ed m o bilit y fina lly

eme rge.

4.2.4 Multi-homing

Mult i-h omi ng is anot he r issu e that is gro win g in

impo rt anc e, but is no t yet crit ica l. A s bu sin es ses c om e

to de pend more and more o n Inte rnet acces s, th e

co nseq ue nce s o f a ne tw ork o ut ag e b ec ome m uch m or e

sever e. I t is natu ral then tha t any co mpan y th at dep end s

on the I ntern et for reven ue wi ll attem pt to pr ovid e

redu nd anc y by co nnec tin g via mo re than one I ntern et

prov i d e r. T his i s not t echnical ly diff icult, and c a n be

ach iev ed by sim ply a nn oun cin g the s am e ad dr ess p refix

via b ot h p rovi d ers. H ow ever , w he n t his i s don e by a

gre at m a ny e dge ne tw orks , t he ef fect is to preve nt

add re ss ag greg at ion in rout in g an noun c emen t s. The

re sult is that the nu mb er o f ad dre ss pref ix es t ha t nee d s

to be rou ted tend s t owa rds the nu mber of e nd netw or ks

in t he wo rld, r athe r than tow ards the n um ber o f lar ge

IS Ps. It is v ery un cle ar, at this m ome nt in tim e, wh eth er

backbone router s or in deed the B GP routing pro toco l

its elf w il l cop e with this m ass ive in crea se i n th e num b er

of adve rtise d rout es .

Th is grow th due to multi-h oming is alre a dy

happen ing. Sh ort of an ar chitectu ral s olution [ 34] to the

pr obl em th at c an u til is e mo re th an one ad dr ess p re fix

fo r ea ch ed ge-s ub ne t, t he gr ow th s eem s c erta in to

con ti nue un aba ted . T he qu esti on th at rema i ns is

whe th er this w ill lead to an in cre ase in rout in g p rob le ms,

or wh ethe r m or e expen siv e ro uting h ard ware c a n keep

ahea d of the grow th.

4.2.5 Architect u ral os sification

Pe rh aps t he bi ggest problem is re lated t o why all the

ot her pr ob lem s h av e no t y et be en a ddr ess ed . Th e

In terne t arc h itect ure h as not ev olve d sig nific ant ly s in ce

the ear ly 19 90s , des pit e a r evolu ti on in the us e o f the

Int e rn e t. NA T s a n d firewalls have made it ha r der t o

depl o y new t ran sp ort p r otoc ols an d ev en ne w

ap plic atio ns . Deep pa cket in spe c tion thre aten s t o mak e

this probl em wor se in future.

E v e n I P i t s e l f i s a f f e c t e d . I P w a s s u p p o s e d t o b e

exte n sibl e thro ugh the use of IP option s, b ut long ag o

the intr oducti on of a hardwar e-assist ed fa st pa t h

thr oug h ro uter f orwa rd in g eng ines m e an t that pack et s

withou t IP op tions wer e forwarde d much fa ster th a n

pack ets wi th I P op tions. T oday, usin g a new IP opti on

woul d a m ou nt t o a den ial -o f-servi ce att ack o n th e

rou tin g p ro ces sor of ma ny f as t r oute rs, a nd so su ch

pa ckets ar e h ighl y lik el y to be fi ltered . T hus IPv4

eff ectiv ely los t th e us e o f its ex tens io n me c hani sm . IPv6

atte mpts to rectif y this by separat ing end-to- end IP

opti ons from hop- by-ho p IP opt ions but depl oyment to

dat e ha s been gla cially slow .

In sho rt, th e In tern et archi te ctu re ha s oss ifie d . Thi s

wou ld p erh aps not b e a pro bl em in it se lf i f it we re n ot fo r

th e f act t hat th e exp ec tat ions and requ ir emen ts p lac ed

on the In tern et hav e not re main ed cons ta nt. T her e ar e

signif icant proble ms that have been bui lding for so me

tim e, but cha ngi ng th e Inter ne t to add res s thes e

probl ems has never bee n harder.

4.3 Lon ger-term problems

There wi ll n o do ubt be ma ny p robl em s th at n eed s ol ving

in t he l o ng t er m. How eve r , fo r th e m o st p ar t it i s ha rd to

see w h at t hese p r oble ms w ill a ct ually be. Th ere is on e

exce p tion to this — ad dres s spa c e depl et ion.

4. 3.1 Ad dr ess sp ace de pl eti on

In the ea rly 1 990 s it be cam e cl ear t ha t the Int er net

wou ld run o u t of IP ad dr esse s. C I DR [3 5] w as a n in te rim

so luti on to t hi s, and ha s bee n qui te su cce ssfu l. T he ri se

of NA Ts, from b ein g co nsid er ed an ug ly h ack t o bein g

nearly ubi quitous, h as a lso red uced the problem

som e wh at, a lth ou gh it h as no t a c tual ly be en a sh or ta ge

of add resses t hat h as e ncour ag ed NA T pro l ifera tion .

The lo ng -ter m solu tio n to the pro ble m of add res s spa ce

depletion is s uppose d to be IP v6. De spite a gre at dea l

of effort, IPv 6 de ploym e nt re main s ra re tod ay. Quit e

sim ply , the re i s no sig nif ica nt inc ent ive t o depl oy IP v6.