1
00:00:00,710 --> 00:00:08,540
In a similar way to our previous example let's assume that C replies to a CC sends a frame to the bridge.

2
00:00:08,660 --> 00:00:14,510
The bridge will read the source MAC address in the frame and then update its MAC address table with

3
00:00:14,510 --> 00:00:15,610
that information.

4
00:00:15,740 --> 00:00:22,730
So the bridge now knows that C is on port 3 as well as knowing that atheism pulled one because it learnt

5
00:00:22,760 --> 00:00:31,730
that from the previous frame and now unlike a hub the bridge does not forward the frame of all ports.

6
00:00:31,820 --> 00:00:33,800
The destination address in the frame is.

7
00:00:34,070 --> 00:00:40,030
The bridge knows that MAC address stays on port 1 so it only forwards the frame out of port 1.

8
00:00:40,250 --> 00:00:43,730
The frame from C therefore only goes out of port 1.

9
00:00:43,880 --> 00:00:50,330
It's not sent out of port to port 4 because the bridge knows that A is on port 1.

10
00:00:50,330 --> 00:00:51,570
So what does this mean.

11
00:00:51,680 --> 00:00:57,190
All subsequent frames from ANC will only use port 1 in 3.

12
00:00:57,200 --> 00:01:02,920
In other words if a sends a nother frame to see it will only go to Port 3.

13
00:01:02,930 --> 00:01:09,020
This is because the MAC addresses of A and C are in the MAC address table and the bridgeable for traffic

14
00:01:09,170 --> 00:01:16,370
based on entries in the MAC address table B and D are no longer receiving frames between A and C frames

15
00:01:16,370 --> 00:01:17,500
from C to A.

16
00:01:17,600 --> 00:01:24,170
Arriving on port three will go to port 1 and frame's from ATC arriving on port one will be sent out

17
00:01:24,170 --> 00:01:32,780
to port 3 day for a and c can have a conversation independently of B and D B and D are no longer receiving

18
00:01:32,780 --> 00:01:33,490
frames S..

19
00:01:33,500 --> 00:01:40,310
Between A and C the frames between A and C are contained between ports 1 and 3.

20
00:01:40,340 --> 00:01:49,580
No bandwidth is used on port 2 and 4 when traffic is sent between A and C devices b and d do not receive

21
00:01:49,610 --> 00:01:50,950
any frames S..

22
00:01:50,960 --> 00:01:58,210
Between A and C and therefore avoid unnecessary processing of frames not destined to themselves.

23
00:01:58,250 --> 00:01:59,700
Bandwidth is being conserved.

24
00:01:59,750 --> 00:02:07,250
Devices are not unnecessarily processing traffic not destined to them and thus bridges have major advantages

25
00:02:07,250 --> 00:02:10,020
over hubs over time.

26
00:02:10,020 --> 00:02:12,920
The bridge will learn where all mac addresses are.

27
00:02:13,110 --> 00:02:19,880
So the bridge will learn that I use import one BS on Portie seasoned port 3 and Ds on port 4.

28
00:02:19,890 --> 00:02:27,250
That means that over time B and D can have a conversation independently of A in C..

29
00:02:27,390 --> 00:02:32,490
The two conversations do not affect each other frames from each conversation.

30
00:02:32,490 --> 00:02:35,670
Do not interfere with the other conversation.

31
00:02:35,730 --> 00:02:42,060
Pay for Biondi can communicate at the same time as a in C.

32
00:02:42,180 --> 00:02:48,630
Now continuing with the advantages of bridges each port is a different collision domain so a collision

33
00:02:48,630 --> 00:02:51,220
on port 1 will not affect port 3.

34
00:02:51,240 --> 00:02:55,270
Each interface on a bridge is a separate collision domain.

35
00:02:55,350 --> 00:03:01,560
So in this example we have one two three four collision domains.

36
00:03:01,560 --> 00:03:08,100
If a and b were having a conversation and a collision took place on port three it will not affect a

37
00:03:08,130 --> 00:03:13,500
and b they wouldn't even realize that there was a collision in the network.

38
00:03:13,530 --> 00:03:17,930
Now in this typology we have a hub connected to port 4 of the bridge.

39
00:03:18,090 --> 00:03:24,690
A hub is a single collision domain so any collisions that take place on the hub will affect two devices

40
00:03:24,690 --> 00:03:30,750
connected to the hub but will not affect other devices elsewhere in the topology.

41
00:03:30,870 --> 00:03:37,980
So if there was a collision on the hub it would affect host E and host D but it would not affect host

42
00:03:38,010 --> 00:03:40,400
a C and B.

43
00:03:40,470 --> 00:03:46,200
The problem with collisions is that if a collision takes place the devices have to back off for a random

44
00:03:46,200 --> 00:03:50,360
period of time and then they need to try and access the network again.

45
00:03:50,400 --> 00:03:56,910
So if these devices DNP are in a single collision domain the bandwidth and throughput that they have

46
00:03:56,910 --> 00:04:05,040
is lower than these devices which are in a separate collision domain by themselves a C and B have a

47
00:04:05,160 --> 00:04:07,190
dedicated link.

48
00:04:07,280 --> 00:04:14,010
They are on a single broadcast domain and single collision domain DNG however are sharing bandwidth

49
00:04:14,130 --> 00:04:21,550
because they connected to a hub host a C and B are on separate collision domains.

50
00:04:21,930 --> 00:04:28,170
Now it's important to remember that a bridge is still a single broadcast domain so if a sent a broadcast

51
00:04:28,410 --> 00:04:31,360
it would be received by everyone in this typology.

52
00:04:31,500 --> 00:04:37,530
All devices will receive the broadcast and in some cases that's a good thing but in most cases it's

53
00:04:37,530 --> 00:04:44,610
not in networking we typically want to restrict or contain broadcast traffic when there are too many

54
00:04:44,610 --> 00:04:46,240
broadcasts in the network.

55
00:04:46,260 --> 00:04:52,260
You can slow down all devices on the network and in the worst cases it will bring your network to its

56
00:04:52,260 --> 00:04:53,100
knees.

57
00:04:53,100 --> 00:04:56,320
In other words your network will just break and not function.

58
00:04:56,400 --> 00:05:03,650
If you have what's called a broadcast storm bridges once again process information in software rather

59
00:05:03,650 --> 00:05:11,180
than in hardware and they tend to be slow in comparison to devices such as switches which process frames

60
00:05:11,420 --> 00:05:19,180
in hardware the number of ports on a bridge is also limited when compared to switches in todays environments.

61
00:05:19,190 --> 00:05:21,660
Switches have essentially replaced bridges.

62
00:05:21,830 --> 00:05:27,200
But it's good for you to realize that a bridge and a switch operate in a very similar way.

63
00:05:27,200 --> 00:05:31,400
So in summary a bridge is a layer 2 device in the oocyte model.

64
00:05:31,400 --> 00:05:33,920
In other words it operates at the data link layer.

65
00:05:34,130 --> 00:05:39,740
It's more intelligent than a hub because it has a mac address table and it learns where MAC addresses

66
00:05:39,740 --> 00:05:46,100
are and then adds those MAC addresses to the MAC address table and can then make intelligent decisions

67
00:05:46,250 --> 00:05:51,900
on which to fall with traffic based on information learned and contained in the MAC address table.

68
00:05:52,080 --> 00:05:58,670
My hubby's a physical device that simply repeat signals out of all ports except the ports in which the

69
00:05:58,670 --> 00:06:00,220
traffic was received.

70
00:06:00,290 --> 00:06:03,520
A bridge will flood a frame out of all ports when it doesn't.

71
00:06:03,530 --> 00:06:05,980
No way to send the frame.

72
00:06:05,990 --> 00:06:09,840
In other words it hasn't learned where the destination MAC address is.

73
00:06:09,860 --> 00:06:17,300
It will also flood broadcasts out of all ports so each port on a bridge is a separate collision domain

74
00:06:17,690 --> 00:06:26,090
but a bridge is still a single broadcast domain switches are very similar to bridges as they both reside

75
00:06:26,090 --> 00:06:30,290
at least to where the data link layer of the overside model.

76
00:06:30,290 --> 00:06:35,360
The big advantage of switching when compared to bridging is that processing can be done in a hot way

77
00:06:35,750 --> 00:06:40,890
using what are called A-6 or application specific integrated circuits.

78
00:06:40,940 --> 00:06:44,510
The number of ports supported by switches is also a lot higher.

79
00:06:44,690 --> 00:06:50,840
Hundreds of ports are supported on certain switches where as with bridges you are limited to a few ports

80
00:06:51,250 --> 00:06:57,590
switches are able to do this because processing is done in hardware and in actual fact these days processing

81
00:06:57,590 --> 00:07:03,920
is done at wire speed which means that there is no degradation of performance between two devices when

82
00:07:03,920 --> 00:07:05,920
they are connected via a switch.

83
00:07:05,930 --> 00:07:11,990
In other words switches can move traffic from one port to another port at the same speed as if they

84
00:07:11,990 --> 00:07:13,480
weren't there.

85
00:07:13,820 --> 00:07:20,420
They can process and switch frames from one port to another port without slowing the frame down.

86
00:07:20,420 --> 00:07:26,830
So here's a quick comparison between switches and bridges switches process and Hadaway using A-6 Brydges

87
00:07:26,870 --> 00:07:32,930
process in software and are therefore a lot slower switcher support many ports bridges are limited in

88
00:07:32,930 --> 00:07:35,190
the number of ports that they support.

89
00:07:35,240 --> 00:07:38,630
Bridges have been replaced by switches in todays networks.