Switch and router technology-02-working principle of Ethernet switch

Catalog

One 、 Ethernet switch

1.1 Early Ethernet

1.2 Hub introduction

1.3 Switched network

1.4 How switches work

1.5 Switch operating mode

1.6 Switch interface rate

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One 、 Ethernet switch

1.1 Early Ethernet

Early Ethernet ： Shared networks

It is made up of hubs （HUB） Connected to a 、 Form a conflict domain / Broadcast area

1.2 Hub introduction

        The main function of the hub is to regenerate the received signal Shaping amplification , With Expand the transmission distance of the network , At the same time, all nodes are concentrated on the nodes centered on it . Working on the physical level , There is no switch like " Intelligent memory " Ability and " Study " Ability . It doesn't have what a switch has MAC Address table , So when it sends data, it's not targeted , It is Send by broadcast , So it is called broadcast domain .

        When different hosts meanwhile Conflicts occur when sending data to the hub , To form a Conflict domain , And the bandwidth is shared .

When the host 1 Host computer 2 When sending data , host 3 Also to the host 4 send data , There will be conflict , And bandwidth sharing .

1.3 Switched network

Now it's using Switched network （ Ethernet switch ）

Adopt broadcast domain , It is simply understood as ： A switch in the same network is a broadcast domain

radio broadcast ： The way of information dissemination , A device in the network , At the same time, a message is sent to all devices in the network

One to many

The network connected by a switch is called in a broadcast domain , Bandwidth will not be shared 、 Working at the data link layer

1.4 How switches work

When the host A to B When sending data , When you get to the switch , from 1 No. 1 interface receives

The switch works on the second floor , So I will check the data link layer , Source and destination in data frame MAC, Then compare one maintained in the switch MAC surface , Check the sender host A Is your address recorded in MAC In the table . If there is no record of learning （ host A— Interface 1）

Continue to check the purpose MAC Address , If not, forward it by broadcasting （ All connection interfaces except switch interface 2、3） get out 、 host B And host C All will receive data

host B and C Data will be unsealed , Check the purpose MAC Is it myself , If it's not your own , Dispose of it

host B Will respond to the switch , Exchange opportunities to view hosts B Source MAC Address , Because there's no record , Will learn to record （ host B— Interface 2） And check the purpose MAC The address is host A, host A stay MAC There are records in the table , Therefore, the switch forwards unicast according to the corresponding interface （ one-on-one ）

If MAC Table has host A and B Of MAC Record , At the beginning, you will find the corresponding port and forward it .

MAC The table maintains the sender's MAC Correspondence between address and interface .

1.5 summary

When the switch receives a data frame , First Learning sources MAC The address records to MAC surface （ Source MAC— Interface number ）, Then proceed Broadcast data frames , All interfaces except the switch receiving interface will receive the broadcast . All interfaces will be de encapsulated by the corresponding host , Check the purpose MAC Is it myself , If so, reseal the data , and Respond To switch , Switch received response , View source MAC Address , and Learning record stay MAC In the table （ Source MAC— Interface number ）, Continue to check the purpose MAC, Find out MAC The table already exists , Then proceed with Unicast forwarding , Forward it according to the corresponding interface , Other hosts that receive broadcast information , Unpack view purpose MAC Not directly Discard processing . Next time, the data will be forwarded directly by unicast forwarding .

1.5 Switch operating mode

Simplex ： Data can only be transmitted in one direction

Half duplex ： Data can be transmitted in both directions , But not at the same time

full duplex ： Data can be transmitted Bi directionally and simultaneously      // At present, they are basically full duplex

1.6 Switch interface rate

10Mbps

100Mbps

1000Mbps