Figure 11-1 Router-on-a-Stick Design

odecrackAI and Robotics

Oct 29, 2013 (3 years and 11 months ago)

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1

whe
n

discussing

Laye
r

3

switching


afte
r

all
,

Laye
r

3

switching

i
s

routing
.

This section

i
s

designe
d

to

serv
e

only

a
s

a

brie
f

reminde
r

o
f

routing'
s

benefit
s

in

a

large
networ
k

(campu
s

o
r

WAN)
.

Fo
r

a

mor
e

thoroug
h

discussion

o
f

thi
s

subject
,

please

see

the

section

"Advantage
s

o
f

Routing
"

in

Chapter

14.


Probably

the

most

important

benefit

of

routing

is

its

pr
o
ve
n

histor
y

o
f

facilitating
large

networks
.

Althoug
h

the

Interne
t

serve
s

a
s

the

obviou
s

exampl
e

here
,

thi
s

point i
s

true

o
f

an
y

typ
e

o
f

network
,

suc
h

a
s

a

large

campu
s

backbone
.

Becaus
e

routers
preven
t

broadcas
t

propagatio
n

an
d

us
e

mor
e

intelligen
t

forwar
d
in
g

algorithm
s

than

bridges
,

router
s

provid
e

muc
h

mor
e

efficien
t

us
e

o
f

bandwidth
.

Thi
s

simultaneously

result
s

in

flexible

an
d

optima
l

pat
h

selection
.

Fo
r

example
,

i
t

i
s

ver
y

eas
y

to

implemen
t

load

balancing

acros
s

multiple

path
s

in

mos
t

network
s

whe
n

usi
n
g

routing
.

O
n

the

othe
r

hand
,

a
s

Chapter

7,

"Advanced

Spanning

Tree,
"

discussed, Laye
r

2

load

balancing

ca
n

b
e

ver
y

difficul
t

to

design
,

implement
,

an
d

maintain
.

The

data

for
w
arding

benefit
s

o
f

router
s

are

especially

importan
t

whe
n

multicas
t

traffi
c

is in

use
.

A
s

multicas
t

traffi
c

become
s

increasingly

commo
n

in

campu
s

networks,

router
s

play

a
n

increasingly

importan
t

role.


Router
s

provid
e

additiona
l

benefit
s

tha
t

reac
h

beyon
d

t
h
e

area

of

data

forwarding.
Becaus
e

Laye
r

3

addresse
s

are

hierarchical
,

router
s

ca
n

b
e

use
d

to

implement summarize
d

designs
.

B
y

reducin
g

routing

protoco
l

overhead
,

increasing

table

lookup performance
,

an
d

improvin
g

networ
k

stability
,

thi
s

ca
n

furthe
r

facil
i
tat
e

network
s

of almos
t

unlimite
d

size
.

Mos
t

router
s

provid
e

extensiv
e

acces
s

lis
t

capabilitie
s

tha
t

can

b
e

use
d

to

provid
e

importan
t

policy

controls
.

Finally
,

router
s

ca
n

also

provide

importan
t

feature
s

suc
h

a
s

DHC
P

relay
,

prox
y

Addres
s

Resolutio
n

Protoc
o
l

(ARP),

an
d

Ge
t

Neares
t

Serve
r

(GNS
)

function
s

in

IPX

networks.


Tip



Yo
u

shoul
d

build

routing

(Laye
r

3

switching
)

into

al
l

bu
t

the

smalles
t

campus networks
.

Se
e

Chapters

14,

"
Campus

Design

Models,
"

an
d

15,"Campus

Design

Implementation,
"

fo
r

mor
e

information.

Route
r
-
o
n
-
a
-
Stick


Early

VLA
N

design
s

relied

o
n

router
s

connecte
d

to

VLA
N
-
capabl
e

switche
s

in

the

manne
r

show
n

in

Figure

1
1
-

1
.



Figure

1
1
-
1

Route
r
-
o
n
-
a
-
Stic
k

Design