Hcia-r & s self use notes (18) campus network architecture foundation, switch working principle, VLAN principle

Infrastructure of campus network （7/22,33min）

Switching technology / Two layer technology

Routing technology is not necessarily a three-tier Technology （ Such as RIP Packaged in UDP 520,OSPF Packaged in IP 89）

The layer-2 switch works at the data link layer , Operate on data frames . After receiving the data frame , The switch will forward the data frame according to the header information of the data frame

When it comes to layer 2 Networks

How switches work （7/22,42min）

The main functions of the switch ：

Access of terminal equipment

Ethernet data frame exchange , According to the purpose MAC Address forwarding data frame ; Study MAC Address , And maintain MAC Address table ;

Prevent layer 2 loop

principle	remarks
Study Learn	When a frame is received from an interface , Put the in frame Source MAC Bind to this interface , Deposit in MAC Address table
flooding Flood	When received from an interface Broadcast frame 、 Multicast frame 、 Unknown unicast frame （ The goal is MAC There is no such thing as MAC In the address table ）, Forward the frame from all other interfaces , Except the receiving port
forward Forward	When received from an interface Known unicast frames , Immediately forward it from the corresponding interface
to update Update	Each record is saved by default 300s The records learned by all interfaces will be cleared after the switch is restarted After the interface is closed, the records learned by the interface will be cleared A source MAC Appear on another interface , Old records will be deleted , Add a new record

Contract awarding means learning , Without any reason ARP It can also make the switch learn MAC Address

Relative switch , If the router finds that there is no target route, it will directly lose packets

dis mac-add agenting-time Check the aging time （ If not, five minutes mac The watch is empty ）

An interface can only learn one of a host mac, May float back and forth

Multicast Optimization Technology , Flood control

Ethernet interface working mode ：

The term	remarks
Half duplex	half-duplex Both sides of the communication can send and receive data , But not at the same time .（ Telephone ）
full duplex	full-duplex Both sides of communication can receive and send data at the same time .（ Walkie-talkie ）
rate	speed Both ends shall negotiate during interface connection , If the negotiation fails, normal communication cannot be performed

Duplex and rate are adaptive by default （negotiation auto）;

Turn off auto negotiation ：

int GigabitEthernet 0/0/1

undo auto-negotiation  or  negotiation auto disable（ Depending on the device version ）

Half duplex may occur CRC And Framements（ Fragmentation ） as well as Collisions（ Conflict , Packet flow conflict ） Wrong package

VLAN principle （7/22,48min）

Vlan（Virtual Local Area Network）, Virtual LAN .

VLAN advantage ：

Effective control of the broadcast domain ; Enhance the security of LAN ; Flexible construction of virtual working groups ; Simplify network management

VLAN summary ：

A physical LAN is logically divided into multiple broadcast domains ;

1 VLAN =1 Broadcast area =1 subnet

The radio won't be in VLAN Forward between , But limited to their own VLAN in

Different VLAN The devices between cannot communicate by default , Layer 3 equipment is required to realize interworking

VLAN Range ：

0-4095, common 4096 individual （0 and 4095 Make reservations ,1 As the default ）

VLAN Label Introduction ：

Ethernet frame source mac Insert a 4 Bytes of tag

Switch to pc Or between switch ports pvid And vlan Consistent time , No tag

VLAN Link type ：

type	remarks
Access Link Access link	Used to connect to Hosts and switches The link to The frames transmitted on the access link are untagged frame
Trunk link main rd / Relay link	be used for Interconnection of switches or Between switch and router （ Single arm routing ） The link to Almost all the frames transmitted on the trunk link are tagged Frames are used for both end recognition

also Hybrid And QinQ Two kinds of

PVID：

namely Port VLAN ID, Represents the default value of the port VLAN

Interface type -Access：

For connecting to the host ;

After receiving the data, it will add VLAN Tag,VLAN ID And the port of PVID identical ;

Will be removed before forwarding data VLAN Tag

host A Send data to the switch , Label the switch 10, Find another one pvid10 Port forwarding , And peel off tag

notes ：

PC Cannot send or receive with tag Frame of （ Can't recognize ）

The switch is labeled only for self identification  

if host A Send the label to the switch as 20 Data packets of , Switch interface （PVID by 10） How to deal with —— take 20 Change it to 10

Interface type -Trunk：

When a frame is received （ Into the direction ）

If the frame does not contain Tag, On the port PVID;

If the frame contains Tag, It doesn't change

When sending a frame （ Exit direction ）, Of the frame VLAN ID stay Trunk In the allowed sending list of ：

If it is connected with the port PVID identical , Then peel off Tag send out ;

If it is connected with the port PVID Different , Send it directly

Carrying multiple vlan Of traffic

Interface type -Hybrid

whole access The mouth can also pass （ The host address should be the same as the network segment ）

You can connect to the host , You can also connect to other switches .

Both access links and trunk links can be connected

Allow multiple VLAN Through the frame of , And can be in the direction of the interface will be some VLAN The frame of Tag be stripped （ Depends on the configuration of the command ）

Special scenes ：

Rely only on Access Interface completion is different VLAN（ But the same network segment ） Host communication ：

The cascade port of the switch is set as above , It can also realize data communication

PC-A→SW1 Gi0/0/1（ Add tags PVID10）→SW1 Gi0/0/2（ Peel off the label PVID 10）→SW2 Gi0/0/1（ Add tags PVID 20）→SW2 Gi0/0/2（ Peel off the label PVID20）→PC-B