chuong 5 - chon duong

7/31/2019 Chuong 5 - Chon Duong

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1

Chn ng

B mn Truyn thng v Mng my tnh

Bi ging c s dng ngun ti liu cung cp bi trng i hc Keio, Nht Bn


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2

Chn ng l g?

Cc nguyn l chn ngC ch chuyn tip gi tin

Quy tc Longest matching


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3

C bn v chn ng (1)

Khi mt my trm gi mt gi tin IP ti mt mykhc

Nu a ch ch nm trn cng mt ng truyn vt l:

Chuyn trc tip Nu a ch ch nm trn mt mng khc: Chuyn gin

tip qua b nh tuyn (chn ng)

Router Router


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4

ch nTmng i

ch n? Tmng i

C bn v chn ng (2)


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5

Chn ng l g?

C ch my trm hay b nh tuynchuyn tip gi tin t ngun n ch

Cc thnh phn ca chn ng Bng chn ng Thng tin chn ng

Gii thut, giao thc chn ng


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6

B nh tuyn?

Thit b chuyn tip cc gi tin gia ccmng L mt my tnh, vi cc phn cng chuyn dng

Kt ni nhiu mng vi nhau

Chuyn tip gi tin da trn bng chn ng

C nhiu giao din

Ph hp vi nhiu dng lu lng v phmvi ca mng


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7

Mt s v d

Cisco 2600

Cisco CRS-1

BUFFALOBHR-4RV

Router mng trc

Router ngoi vi

Router c trung

Juniper M10

Cisco 3700

Foundry NetworksNetIron 800

Hitachi

GR2000-1B

YAMAHA

RTX-1500

PLANEXGW-AP54SAG

http://www.cisco.com.vn

http://www.juniper.net/

http://www.buffalotech.com
http://www.buffalotech.com/http://www.cisco.com.vn/http://www.juniper.net/http://www.buffalotech.com/http://www.buffalotech.com/http://www.juniper.net/http://www.cisco.com.vn/


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8

Bng chn ng

Ch ra danh sch cc ng i c th,c lu trong b nh ca router

Cc thnh phn chnh ca bng chn

nga ch ch/mt n mng Router k tip


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9

RouterB

Network Next-hop

10.0.0.0/24 A

172.16.0.0/24 C

RouterCRouterA

10.0.0.0/24 192.168.0.0/24 172.16.0.0/24

10.0.0.0/24 172.16.0.0/24

Bng chn ng v c chchuyn tip (1)

Lu quy tc: No routes, no reachability!


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10

Quy tc Longest matching(1)

Gi s mt a ch mng ch li c nhiu hnmt mc trong bng chn ng

a ch ch : 11.1.2.5

Router k tip no s c s dng?

Network Next hop

11.0.0.0/8 A11.1.0.0/16 B

11.1.2.0/24 C


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11

Quy tc Longest matching(2)

a ch ch:11.1.2.5 = 00001011.00000001.00000010.00000101

ng i 1:

11.1.2.0/24 = 00001011.00000001.00000010.00000000ng i 2:11.1.0.0/16 = 00001011.00000001.00000000.00000000

ng i 3:

11.0.0.0/8 = 00001011.00000000.00000000.00000000

Longest matching l g?Ti sao phi cn quy tc ny?


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12

RouterB

Network Next-hop

10.0.0.0/24 A

172.16.0.0/24 C

192.168.0.0/24 Direct

RouterCRouterA

10.0.0.0/24 192.168.0.0/24 172.16.0.0/24

10.0.0.0/24 172.16.0.0/24

Bng chn ng v c chchuyn tip (2)

Q.M t bng chnng trn C

Nu C ni voInternet?

Internet


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13

ng i mc nh

Nu ng i khng tm thy trong bng chnng ng i mc nh tr n mt router kt tip

Trong nhiu trng hp, y l ng i duy nht 0.0.0.0/0

L mt trng hp c bit, ch tt c cc ng i

Internet

Router A

Router k tip lun l A


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14

Kt hp ng i (Routingaggregation)

200.23.1.0/24

200.23.2.0/24

200.23.3.0/24

200.23.4.0/24

200.23.0.0/22

200.23.0.0/23

200.23.2.0/23

C bao nhiu mng con trn mng Internet?

S c rt nhiu mc trong bng chn ng?

Cc mng con k tip vi cng a ch ch c th c tng

hp li lm gim s mc trong bng chn ng.


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15

Kt hp ng i (2)

V d v Viettel Khng gian a ch IP: kh ln

203.113.128.0-203.113.191.255

kt ni n mt mng con ca Vietel (khchhng): Ch cn ch ra ng i n mng Viettel

ng i mc nh chnh l mt dng ca vic

kt hp ng 0.0.0.0/0


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16

V d v bng chn ng my trm

C:\Documents and Settings\hongson>netstat -rn

Route Table

===========================================================================

Interface List

0x1 ........................... MS TCP Loopback interface0x2 ...08 00 1f b2 a1 a3 ...... Realtek RTL8139 Family PCI Fast Ethernet NIC -

===========================================================================

Active Routes:

Network Netmask Gateway Interface Metric

0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.34 20

127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1

192.168.1.0 255.255.255.0 192.168.1.34 192.168.1.34 20192.168.1.34 255.255.255.255 127.0.0.1 127.0.0.1 20

192.168.1.255 255.255.255.255 192.168.1.34 192.168.1.34 20

224.0.0.0 240.0.0.0 192.168.1.34 192.168.1.34 20

255.255.255.255 255.255.255.255 192.168.1.34 192.168.1.34 1

Default Gateway: 192.168.1.1

===========================================================================


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17

#show ip route

Prefix Next Hop

203.238.37.0/24 via 203.178.136.14

203.238.37.96/27 via 203.178.136.26203.238.37.128/27 via 203.178.136.26

203.170.97.0/24 via 203.178.136.14

192.68.132.0/24 via 203.178.136.29

203.254.52.0/24 via 203.178.136.14202.171.96.0/24 via 203.178.136.14

V d v bng chn ng Router (trch)


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18

Chn ng tnh v chnng ng

Chn ng tnhChn ng ng

u im nhc im


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19

Router B

Network Next-hop

10.0.0.0/24 A

172.16.0.0/24 C

Router CRouter A

10.0.0.0/24 192.168.0.0/24 172.16.0.0/24

Network Next-hop

10.0.0.0/24 B

192.168.0.0/24 B

Network Next-hop

192.168.0.0/24 B

172.16.0.0/24 B

Vn cp nht bng chn ng S thay i cu trc mng: thm mng mi, mt nt mng

b mt in S cn thit phi cp nht bng chn ng

Cho tt c cc nt mng (v l thuyt) Thc t, ch mt s nt mng phi cp nht

172.16.1.0/24

172.16.1.0/24 B 172.16.1.0/24 C

New Network


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20

Lm th no cp nht?

Chn ng tnh Cc mc trong bng chn ng c sa i

th cng bi ngi qun tr

Chn ng ng T ng cp nht bng chn ng

Bng cc giao thc chn ng


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Chn ng tnh

Khi c s c: Khng th ni vo

Internet k c khi c tnti ng i d phng

Ngi qun tr mng cnthay i

Internet

Next-hop 10.0.0.3

10.0.0.1

10.0.0.3 10.0.0.2

Next-hop 10.0.0.1

Bng chn ng ca 10.0.0.1 (1 phn)

Prefix Next-hop

0.0.0.0/0 10.0.0.3

Kt ni b li


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22

Chn ng ng

Khi c s c: ng i thay th c cp

nht mt cch t ng

Bng chn ng ca 10.0.0.1 (1 phn)

Prefix Next-hop

0.0.0.0/0 10.0.0.2

0.0.0.0/0 10.0.0.3 Kt ni b li

Kt ni d phng

Internet

Next-hop 10.0.0.3

10.0.0.1

10.0.0.3 10.0.0.2

Next-hop 10.0.0.1


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23

c im ca chn ng tnh

u n nh An ton

Khng b nh hng bi cc yu t tc ng

Nhc

Cng nhc Khng th s dng t ng kt ni d phng Kh qun l


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24

Chn ng ng

u D qun l

T ng s dng kt ni d phng

Nhc Tnh an ton

Cc giao thc chn ng phc tp v kh hiu Kh qun l


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25

Cc gii thut v giaothc chn ng

Gii thut Dijkstra v Bellman-FordGiao thc dng link-state v dng

distance-vector


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26

Biu din mng bi th

u

yx

wv

z2

2

13

1

1

2

53

5

th vi cc nt (b nh tuyn) v cc cnh (linkt)

Chi ph cho vic s dng mi lin kt c(x,y) Bng thng, tr, chi ph, mc tc nghn

Gi thut chn ng: Xc nh ng i ngn nhtgia hai nt bt k


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27

Cy ng i ngn nht - SPT

SPT Shortest Path Tree Cc cnh xut pht t nt gc v ti cc l ng i duy nht t nt gc ti nt v, l ng i ngn nht

gia nt gc v nt v Mi nt s c mt SPT ca ring nt

yx

w

u zu

yx

wv

z2

2

1 3

1

1

2

53

5

v


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28

Tp trung hay phn tn

Tp trung Thu thp thng tin vo mt nt mng S dng cc gii thut tm ng i trn th Phn b bng chn ng t nt trung tm ti

cc nt

Phn tn Mi nt t xy dng bng chn ng ring Giao thc chn ng: Link-state hoc distance-

vector

c s dng ph bin trong thc t


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Tp trung hay phn tn

Thng tin chn ngl cn thit xy dngbng chn ng

Tp trung hay phn tn?

Tp trung: Mi router c thng tin y v trng thi ca mng

Gii thut dnglink state

Phn tn:

Cc nt ch bit c trng thi ca lin kt vt l ti nt kbn

Lin tc lp li vic tnh ton v trao i thng tin vi nt kbn

Gii thut dngdistance vector

Bn ca bn cng l bn


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31

K hiu

G = (V,E) : th vi tp nh Vv tp cnh E

c(x,y):chi ph ca lin kt xti y; = nu khngphi 2 nt k nhau

d(v):chi ph hin thi ca ng i t nt ngun tint ch. v

p(v):nt ngay trc nt vtrn ng i t ngun tich

T:Tp cc nt m ng i ngn nht c xcnh


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Cc th tc

Init():

Vi mi nt v, d[v]= , p[v]= NIL

d[s]= 0

Improve(u,v), trong d (u,v) u, v l mt cnhno ca Gifd[v] > d[u] + c(u,v) then

d[v] = d[u] + c(u,v)

p[v] = u


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Dijsktras Algorithm

1. Init() ;2. T= ;3. Repeat4. u: u T | d(u)l b nht ;5. T = T {u};6. for all vneighbor(u) v vT7. update(u,v) ;

8. UntilT = V


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Dijkstras algorithm: V d

Step0

1

2

3

45

Tu

ux

uxy

uxyv

uxyvwuxyvwz

d(v),p(v)2,u

2,u

2,u

d(w),p(w)5,u

4,x

3,y

3,y

d(x),p(x)1,u

d(y),p(y)

2,x

d(z),p(z)

4,y

4,y

4,y

yx

w

u z

u

yx

wv

z

2

21

3

1

1

2

53

5

vv

x

y

w

z

(u,v)

(u,x)

(u,x)

(u,x)

(u,x)

destination link

Bng chn ng ca u:

SPT ca u:


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Gii thut dng distance-vector (1)

Phng trnh Bellman-Ford (quy hoach ng)

nh ngha

dx(y) := chi ph ca ng i ngn nhtt x ti y

Ta c

dx(y) = min {c(x,v) + dv(y) }

cho tt c cc v l hng xm ca x

v


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36

Minh ha Bellman-Ford Eq.

u

yx

wv

z2

21

3

1

1

2

53

5

D thy, dv(z) = 5, dx(z) = 3, dw(z) = 3

du(z) = min { c(u,v) + dv(z),c(u,x) + dx(z),

c(u,w) + dw(z) }

= min {2 + 5,

1 + 3,

5 + 3} = 4

Nt no lm gi tr trn nh nhtLa chn lnt k tip trong bng chn ng

B-F eq. cho ta bit:


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Gii thut dng distance-vector (2)

tng c bn: DV: Vector khong cch, tm coi l

ng i ngn nht ca t mt nt tinhng nt khc

Mi nt nh k gi DV ca n ti ccnt bn cnh

Khi nt x nhn c 1 DV, n s cpnht DV ca n qua pt Bellman-ford

Vi mt s iu kin, c lng Dx(y)s hi t dn n gi tr nh nhtdx(y)

Ch(Thay i trong DV cant bn cnh)

Tnh lic lng DV

Nu DV thay i, Bochont bn cnh

Mi nt:


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D ( ) i { ( ) D ( ) ( ) D ( )} D (z) min{c(x y)


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x y z

x

y

z

0 2 7

t

chi ph ti

t

t

x y zx

y

z

0 2 3

t

chi ph tix y z

x

y

z

0 2 3

t

chi ph ti

x y zx

y

z

chi ph ti

x y zx

y

z

0 2 7

t

chi ph ti

x y z

x

y

z

0 2 3

t

chi ph ti

x y z

x

y

z

0 2 3

t

chi ph tix y z

x

y

z

0 2 7

t

chi ph ti

x y z

x

y

z 7 1 0

chi ph ti

2 0 1

2 0 1

7 1 0

2 0 1

7 1 0

2 0 1

3 1 0

2 0 1

3 1 0

2 0 1

3 1 0

2 0 1

3 1 0

thigian

x z12

7

y

nt x

nt y

nt z

Dx(y) = min{c(x,y) + Dy(y), c(x,z) + Dz(y)}

= min{2+0 , 7+1} = 2

Dx(z) =min{c(x,y) +Dy(z), c(x,z) + Dz(z)}

= min{2+1 , 7+0} = 3

S h ii th t LS DV


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So snh cc gii thut LS v DV

Thng ip trao i LS:n nt, E cnh, O(nE)thng ip

DV: Ch trao i gia cchng xm

Thi gian hi t thayi

Tc hi t LS:Thut ton: O(n2) cn

O(nE) thng ip DV: Thay i

S chc chn:Gii s mtrouter hot ng sai

LS:

nt gi cc chi ph sai

Mi nt tnh ring bng

chn ng -> c v chcchn hn

DV:

DV c th b gi sai

Mi nt tnh ton da trncc nt khc

Li b lan truyn trongmng