Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing...
Transcript of Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing...
![Page 1: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/1.jpg)
1
Routing and Internetworking
![Page 2: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/2.jpg)
2
A Network
network/subnet 1
network/subnet 2
gatewayrouter
router
host
H1 R1
R2H2
H3 H4
R3 R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
gatewaylinks networks together to forminternet
routing plans path through network
![Page 3: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/3.jpg)
3
Internets
An internet can be
homogeneous internets
all same type of network
no need to convert frames
heterogeneous internets
free mix of network technologies
need to convert between frame formats
convert between CO and CL?
![Page 4: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/4.jpg)
4
Switching the Data
circuit switched networks
physical communication channel to be set up between two hosts
wasteful if bursty data
e.g. PSTN
message switched networks
sends data inmessages, which can share a channel
store-and-forward
e.g. Post Office
packet switched networks
similar to message switching
limit on size→ data sent in one or morepackets
![Page 5: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/5.jpg)
5
Store-and-forward (1)
time t
R
R
![Page 6: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/6.jpg)
6
Store-and-forward (2)
time t + 1
R
R
![Page 7: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/7.jpg)
7
Store-and-forward (3)
time t + 2
R
R
![Page 8: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/8.jpg)
8
Store-and-forward (4)
time t + 3
R
R
delay∝ packet size
![Page 9: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/9.jpg)
9
Example: Reducing Store-and-forward Delays
A router operating on a PSN using store-and-forward has links into it operating
at 1Mbs−1, and the router is found to delay packets by0.1s. How many pieces
must you fragment the packet into to reduce this delay to0.02s, and how large are
those packets?
delay ∝ packet size
delaypacket size = constant
0.1/1 = 0.02/s → s = 0.2, hence 5 packets are required for each of the old
packets
packet size= delay = 0.02×1×106
8= 2500 bytes
![Page 10: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/10.jpg)
10
Virtual Circuits
net 2
L7
L8
L13
L14
L15
L16
L18
L9
L10
L12
L17
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
R7
to/from from/to
R6
to/from from/to
R4
to/from from/to
R5
to/from from/to
Virtual Circuits allow some features of
CO to be present in PSN
Divide links byvirtual circuitidentifiers (VCI )
Lx(1), Lx(2), Lx(3), . . .
Connect links up VCIs
![Page 11: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/11.jpg)
11
Virtual Circuits
net 2
L7
L8
L13
L14
L15
L16
L18
L9
L10
L12
L17
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
R7
to/from from/to
L10(1) L9(1)
R6
to/from from/to
L9(1) L17(1)
R4
to/from from/to
L12(1) L10(1)
R5
to/from from/to
Connect H5 ↔ H9
![Page 12: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/12.jpg)
12
Routing Tables for VC
net 2
L7
L9
L10
L12
L13
L15
L16
L18
L8
L14
L17
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
H5 ↔ H9
R7
to/from from/to
L10(1) L9(1)
R6
to/from from/to
L9(1) L17(1)
L8(1) L17(2)
R4
to/from from/to
L12(1) L10(1)
R5
to/from from/to
L14(1) L8(1)
Connect H6 ↔ H9
![Page 13: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/13.jpg)
13
Routing Tables for VC
net 2
L7
L8L10
L12 L14
L15
L16
L18L13
L9
L17
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
H5 ↔ H9 H6 ↔ H9
R7
to/from from/to
L10(1) L9(1)
L13(1) L9(2)
R6
to/from from/to
L9(1) L17(1)
L8(1) L17(2)
L9(2) L17(3)
R4
to/from from/to
L12(1) L10(1)
R5
to/from from/to
L14(1) L8(1)
Connect H11 ↔ H9
![Page 14: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/14.jpg)
14
Worksheet: Virtual Circuit Identifiers
switchlink1
-link2
1 3
-link3
switchlink1
�link2
4
4
link3
6
switchlink1
-link2
3 1
-link3
switchlink1
�link2
5 2
�link3
![Page 15: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/15.jpg)
15
The OSI Internetworking Model
Layer Host
Network
Data Link
Physical - -
?
?
?
?
Transmission Medium
Gateway
�R
6
6
6
?
?
?
Host Sub-Layer
SNDAP
SNDCP
SNICP6
6
6
6
Subnetwork Independent Convergence Protocol(SNICP)
Subnetwork Dependent Convergence Protocol(SNDCP)
Subnetwork Dependent Access Protocol(SNDAP)
![Page 16: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/16.jpg)
16
Fragmentation
header 8128 bytes data
Token Bus
Ethernet ?
?
?
?
?
?
header1500 bytes
data
header1500 bytes
data
header1500 bytes
data
header1500 bytes
data
header1500 bytes
data
header728 bytes
data
![Page 17: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/17.jpg)
17
Homogeneous Internetworking: Network Layer
Layer Host
Application
Presentation
Session
Transport
Network
Data Link
Physical
Layer
7
6
5
4
3
2
1- - - -�W
6
�
?
W
?
?
?
?
?
?
Transmission Medium
Repeater
Bridge
Router
Host
6
6
6
6
6
6
![Page 18: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/18.jpg)
18
Homogeneous Internetworking: Data Link Layer
Layer Host
Application
Presentation
Session
Transport
Network
Data Link
Physical
Layer
7
6
5
4
3
2
1- - - -�W
6
�
?
W
?
?
?
?
?
?
Transmission Medium
Repeater
Bridge
Router
Host
6
6
6
6
6
6
![Page 19: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/19.jpg)
19
Homogeneous Internetworking: Physical Layer
Layer Host
Application
Presentation
Session
Transport
Network
Data Link
Physical
Layer
7
6
5
4
3
2
1- - - -�W
6
�
?
W
?
?
?
?
?
?
Transmission Medium
Repeater
Bridge
Router
Host
6
6
6
6
6
6
![Page 20: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/20.jpg)
20
Repeater (1)
timet1
dataH2 H1
H3
R
H2
R
H1
‘repeats’ frames bit by bits; no processing of frames or routing
![Page 21: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/21.jpg)
21
Repeater (2)
timet2
dataH2 H1
H3
R
H2
R
H1
![Page 22: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/22.jpg)
22
Repeater (3)
timet3
dataH2 H1
H3
R
H2
R
H1
also calledhub
![Page 23: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/23.jpg)
23
Bridge (1)
timet1
dataH2 H1
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H3 H1
H2
net 2 net 1
H2 H1
H3
copies frames as required; store-and-forward
![Page 24: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/24.jpg)
24
Bridge (2)
timet2
dataH2 H1
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H3 H1
H2
net 2 net 1
H2 H1
H3
![Page 25: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/25.jpg)
25
Bridge (3)
timet3
data
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H3 H1
H2
net 2 net 1
H2 H1
H3
also calledswitched hub
![Page 26: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/26.jpg)
26
Worksheet: Bridges Reduce Network Load
C1 C2 S2
S1 C3 C4
network bridge
C3 C2 S2
S1 C1 C4
subnet2subnet1
C1 C2 C3 C4
S1 5 22 22 5
S2 17 5 5 19
Total load= 5+22+22+5+17+5+5+19=100%
Subnet 1=Total load-Subnet 2=100-(17+19)=64%
Subnet 2=Total load-Subnet 1=100-(22+22)=56%
![Page 27: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/27.jpg)
27
Bridges and Network Load
To
H1 H2 H3 H4 H5 H6
H1 0 300 10 0 20 0
H2 300 0 10 0 100 10
From H3 10 10 0 200 5 95
H4 10 5 300 0 5 15
H5 60 815 15 5 0 5
H6 0 15 500 5 15 0
![Page 28: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/28.jpg)
28
Using Routing Algorithms & Internetworking
backbone
AS 2
AS 3AS 1
net 1 net 2
net 3
net 4
IGP1
IGP1
IGP3
IGP3
R R
R
R
EGP
EGP
EGP
EGP
EGP
R
R
R
IGP2
G
G
G
R
R
net 5
net 6
R R
net 7 net 8
![Page 29: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/29.jpg)
29
Routing Algorithm: Objectives
H1 R1
R2H2
H3 H4
R3 R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
correctness it finds a valid route
robustness should some part of the network fail, it still finds a route
simplicity must be able to analyse
stability no ‘stampedes’ down a link
fairness each host gets a share if network busy
optimality route minimises the network resources used
![Page 30: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/30.jpg)
30
Costing a route
Often there will be a choice of how to get from A to B
RA
R1
R2
RB
bandwidth avoid links with less free bandwidth
delay take links which take shorter time
price use links with less charge per byte
priority prefer some data over a particular link
![Page 31: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/31.jpg)
31
Two Basic Approaches
adaptive routing has each router adapting its routing according to network
load.
isolated adaptive routingmakes decisions purely on information about
the local node
distributed adaptive routing pass information between the nodes
nonadaptive routing
routers always taking the same action to route packets
aka static routing
![Page 32: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/32.jpg)
32
Flood Routing (1)
1
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
Send the data down all links except that it arrived on
![Page 33: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/33.jpg)
33
Flood Routing (2)
2
2
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
![Page 34: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/34.jpg)
34
Flood Routing (3)
3
3
3
3
3R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
![Page 35: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/35.jpg)
35
Flood Routing (4)
4
4 4 4
4 44 4
R4
R7
R5
R6
H5 H6
H7
H8
H9H10H11
Avoid loops by
recording hop count
recording where packet has been
![Page 36: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/36.jpg)
36
Worksheet: Flood Routing
H1
H2
switch switch switch
switch switch switch
0
![Page 37: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/37.jpg)
37
Source Route
ring 1 ring 2
ring 3
ring 4
ring 5
H1 H2
H3
H4
H5
H6
H7
H8
H4H1
![Page 38: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/38.jpg)
38
Source Route
ring 1 ring 2
ring 3
ring 4
ring 5
H1 H2
H3
H4
H5
H6
H7
H8
H4H1H2
![Page 39: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/39.jpg)
39
Source Route
ring 1 ring 2
ring 3
ring 4
ring 5
H1 H2
H3
H4
H5
H6
H7
H8
H4H1H2H5
H4H1H2H3
![Page 40: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/40.jpg)
40
Source Route
ring 1 ring 2
ring 3
ring 4
ring 5
H1 H2
H3
H4
H5
H6
H7
H8
H4H1H2H5H6
H4H1 via H2H3
![Page 41: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/41.jpg)
41
Backwards Learning and Transparent Bridges (1)
timet1
dataH2 H1
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2 net 2 net 1
if don’t know where host is, flood network
bridges learn where you are
![Page 42: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/42.jpg)
42
Backwards Learning and Transparent Bridges (2)
timet2
dataH2 H1
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2 net 2 net 1
H1
if don’t know where host is, flood network
bridges learn where you are
![Page 43: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/43.jpg)
43
Backwards Learning and Transparent Bridges (3)
timet3
dataH2 H1
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H1
net 2 net 1
H1
if don’t know where host is, flood network
bridges learn where you are
![Page 44: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/44.jpg)
44
Backwards Learning and Transparent Bridges (4)
timet1
dataH1 H2
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H1
net 2 net 1
H1
reply teaches bridges where distination was
![Page 45: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/45.jpg)
45
Backwards Learning and Transparent Bridges (5)
timet2
dataH1 H2data
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H1
H2
net 2 net 1
H2 H1
reply teaches bridges where distination was
![Page 46: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/46.jpg)
46
Backwards Learning and Transparent Bridges (6)
timet3
dataH1 H2
H3
B2
H2
B1
H1
net 3 net 2 net 1
net 3 net 2
H1
H2
net 2 net 1
H2 H1
reply teaches bridges where distination was
![Page 47: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/47.jpg)
47
Worksheet: Backwards Learning
H1 H2 H3 H4
NetworkN1 NetworkN2
NetworkN5NetworkN4
NetworkN3
B1 B2H5
H6 H7 H8 H9B4B3
Host Network
H1 N1
B1
Host Network
H1 N3
B2
Host Network
H1 N3
B3
Host Network
H1 N3
B4
![Page 48: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/48.jpg)
48
Distance Vector
CostC
R1 R2 Rm
Cost to reachRm
held inR2
Cost C=cost to neighbour+value in neighbour’s distance vector
Recompute local distance vector as distribute to neighbours
![Page 49: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/49.jpg)
49
Distance Vector (1)
1
1
2
2
1
1
1
R1
R2
R3
R4
R5
R6
To
R1 R2 R3 R4 R5 R6
R1 0 0 0 0 0 0
R2 0 0 0 0 0 0
From R3 0 0 0 0 0 0
R4 0 0 0 0 0 0
R5 0 0 0 0 0 0
R6 0 0 0 0 0 0
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 1 1 1
R2 1 0 1 1 1 1
From R3 1 1 0 1 1 1
R4 1 1 1 0 1 1
R5 1 1 1 1 0 1
R6 1 1 1 1 1 0
![Page 50: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/50.jpg)
50
Distance Vector (2)
1
1
2
2
1
1
1
R1
R2
R3
R4
R5
R6
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 1 1 1
R2 1 0 1 1 1 1
From R3 1 1 0 1 1 1
R4 1 1 1 0 1 1
R5 1 1 1 1 0 1
R6 1 1 1 1 1 0
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 2 2 2
R2 1 0 2 2 2 2
From R3 1 2 0 2 1 2
R4 2 2 2 0 2 1
R5 2 2 1 2 0 1
R6 2 2 2 1 1 0
![Page 51: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/51.jpg)
51
Distance Vector (3)
1
1
2
2
1
1
1
R1
R2
R3
R4
R5
R6
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 2 2 2
R2 1 0 2 2 2 2
From R3 1 2 0 2 1 2
R4 2 2 2 0 2 1
R5 2 2 1 2 0 1
R6 2 2 2 1 1 0
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 3 2 3
R2 1 0 2 2 3 3
From R3 1 2 0 2 1 2
R4 3 2 2 0 2 1
R5 2 3 1 2 0 1
R6 3 3 2 1 1 0
![Page 52: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/52.jpg)
52
Distance Vector: Poor Response to Failures
1 1R1 R2 R3
To
R1 R2 R3
R1 0 1 2
From R2 1 0 1
R3 2 1 0
To
R1 R2 R3
R1 0 ∞ ∞
From R2 3 0 1
R3 2 1 0
![Page 53: Routing and Internetworking - Imperial College Londonpjm/nac/lecture_routing.pdf · Using Routing Algorithms & Internetworking backbone AS 2 AS 1 AS 3 net 1 net 2 net 3 net 4 IGP1](https://reader034.fdocuments.net/reader034/viewer/2022042103/5e80ff8ab7a6d071ee437c09/html5/thumbnails/53.jpg)
53
Link State
1
1
2
2
1
1
1
R1
R2
R3
R4
R5
R6
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 ? ? ?
R2 1 0 ? 2 ? ?
From R3 1 ? 0 2 1 ?
R4 ? 2 2 0 ? 1
R5 ? ? 1 ? 0 1
R6 ? ? ? 1 1 0
To
R1 R2 R3 R4 R5 R6
R1 0 1 1 3 2 3
R2 1 0 2 2 3 3
From R3 1 2 0 2 1 2
R4 3 2 2 0 2 1
R5 2 3 1 2 0 1
R6 3 3 2 1 1 0