Review and arrangement of HCIA

Abstract language （ written words , video , Pictures, etc ） --- Electrical signals （ Languages that computers can recognize ）

Abstract language --- code             application layer

code       --- Binary system           The presentation layer

Binary system   --- Electrical signals medium （ Hardware ） Access control layer

Process electrical signals                       The physical layer

OSI/RM -- Open system interconnection reference model

ISO --- International Organization for Standardization (1979 year )  //IBM First to launch SNA Reference model

The core idea --- layered

--- Different functions belonging to the same layer have the same or similar purposes and functions ; Each layer provides higher-level services on the basis of the services provided by the next layer , The top layer provides human-computer interaction application services

Open system interconnection reference model
application layer — Provide various application services , Convert abstract language into code , Provide interactive instructions for others
The presentation layer — Convert the encoding to binary
The session layer — Maintain session links between web applications and web servers
Transport layer — Realize end-to-end communication — Port number —0—6535 — among 0 Not as a port of the transport layer
No. use , therefore , The real value range of the port number is 1—65535—— among 1—1023 It's called a well-known port
Number — SPORT, DPORT
The network layer — Use IP Address realizes logical addressing between hosts —— SIP, DIP
obtain DIP Address method :
                1, Know the server directly P Address
                2, Access the server through the domain name
                3, Access the server through the application
                4, radio broadcast
Data link layer — Control physical hardware , Convert binary to electrical signal . In Ethernet , The data link layer needs to pass MAC Address in                           Row physical addressing -48 Bit binary structure

                         1, The only global ;2, use the same pattern
 
obtain DMAC Methods — ARP agreement —-— Address resolution protocol
positive ARP — adopt IP The address for MAC Address
         First , The host sends... In the form of broadcast ARP request , Based on the known P Address , Call for MAC Address . All devices in the broadcast domain can receive request packets , All devices that receive packets will record the source in the packet P Address and source MAc The correspondence of the address is related to the local ARP The cache table . after , Look at the request p Address , If it's local P Address , Will be performed ARP The reply , Local MAc Address inform . If it's not local P Address , The packet will be discarded directly . And , When sending data again , Give priority to local ARP Cache table , If there are records in the table , Then the information will be sent directly according to the record , If there is no record , Then send ARP Request package acquisition MAC Address .
reverse ARP … adopt MAC The address for P Address
free ARP ——1, Self introduction. ;2, Detect address conflicts .
The physical layer —— Handle the transmission of electrical signals
TCP/IP Model
TCP/IP Protocol cluster

Four layer model ---- TCP/IP The standard model

Five layer model ----TCP/IP peer model

PDU Protocol data unit   //TCP Protocol cluster

L1PDU

L2PDU

… L7PDU

application layer --- message

Transport layer --- paragraph

The network layer --- package

Data link layer --- frame

The physical layer --- Bit stream

Encapsulation and de encapsulation

application layer ---- According to the application requirements

Transport layer --- Port number -- TCP/UDP

The network layer --- IP Address --- IP

Data link layer --- MAC Address --- Ethernet protocol Ethernet ： Early LAN

Solutions for , Now it is also used in Wan . Is to rely on MAC Address addressable Layer-1 and layer-2 networks .

The physical layer --- No encapsulation required , Binary conversion to electrical signal

TCP/P The model supports layer collapse encapsulation , And in the OSI Not in the middle ,… Cross layer packaging is generally used in close proximity direct connection devices
Send messages between devices , It can improve the forwarding efficiency .
1, Cross four layer packaging - OSPF -— 89
2, Span three , Four layer package —— STP

  Ethernet Ⅱ Type frame （ Data link layer ）

 

IEEE:

SOF -— Frame header delimiter
DSAP -… Indicate what protocol the upper layer of the device receiving the data frame uses to process the data
SAP —… Indicates the protocol generated by the upper layer of the device that sends the data frame
Control - 1, Connectionless mode ; 2, Connection oriented pattern —— It can realize the fragment reorganization of data packets

Type --- The protocol type used by the upper layer

 Preamble --- Forerunner

IP Address
IPV4 -—32 Bit binary structure —- dotted decimal
IPV6 - 128 Bit binary structure —- It's hexadecimal
Network bit —-- The network bits are the same , It means in the same broadcast domain
Host bit —-- In the same broadcast domain , Use the host bit to distinguish different hosts
Subnet mask —-— Continuous 1 And continuous 0 form ,1 On behalf of network bit ,0 Represents the host bit

IP Classification of addresses --------A,B,C,D,E

A,B,C --- Unicast address --- It can be used as a source IP Can also be a goal IP（ No category IP）

D --- Multicast address --- Only as a goal IP Use , Cannot be used as a source IP Use

E --- Reserved address

unicast --- one-on-one

Multicast -- One to many （ The same multicast group ）

radio broadcast -- A pair of all （ All in the broadcast domain ）

A：0XXX XXXX （0 - 127 ） 1 - 126

B：10XX XXXX 128 - 191

C：110X xxxx 192 - 223

D：1110 XXXX 224 - 239

E：1111 XXXX 240 - 255

A：255.0.0.0

B：255.255.0.0

C：255.255.255.0

stay IP In the address space , Part of it IP The address is called private IP Address ( The private network IP Address ), The rest are called
public IP Address ( Public network IP Address )-— We habitually use private networks P The network built by address is called private
network , Use the public network IP The network built by address is called public network .-— Private address can be reused , But in
The uniqueness of the private network must be guaranteed .
A: 10.0.0.0—10.25.255.255 amount to 1 individual A Class segment
B: 172.16.0.0—172.31.25.255 amount to 16 individual B Class segment
C: 192.168.0.0—192.168.255.255 amount to 256 individual C Class segment

special IP Address

1,127.0.0.0 - 127.255.255.255 --- Loopback address ---- It is mainly used to detect , test

2,255.255.255.255 --- Restricted broadcast address --- Limited by routers --- Only as a target IP Use

3, All the hosts 1 --- 192.168.1.255 --- Direct address （ Cross routing ）--- Only for the purpose mark IP Use （ In principle, it will forward , For security reasons, it will not forward ）

4, All the hosts 0 --- 192.168.1.0 --- Network segment --- network number

5,0.0.0.0 ---- 1, It means there is no IP（DHCP You can use ）;2, Can represent all IP

6,169.254.0.0/16 --- Automatic private address / Local link address （ Communication depends on the surrounding network environment ）

 

ARP The classification of

positive ARP： adopt IP The address for MAC Address

reverse ARP： adopt MAC The address for IP Address RARP

free ARP： Use positive ARP working principle 1, Self introduction. ;2, Detect address conflicts

VLSM --- Variable length subnet mask （ Subnet partition ）

CIDR --- No inter domain routing （ Summary ）

Take the same , Go different

Static routing ： Routing entries manually configured by the network administrator

Dynamic routing ： All routers run the same routing protocol , Then communicate through routers , Finally, the routing entry is calculated .

Advantages of static routing ：1, No additional resources are required

                         2, Static routing is more secure

                         3, The routing administrator selects , Relatively better control

              shortcoming ：1, In a complex network environment , Large amount of configuration

                        2, Static routing cannot automatically converge based on the change of network topology

Advantages of dynamic routing ：1, Dynamic routing can automatically converge based on the change of topology

                         2, Simple configuration

              shortcoming ：1, Need additional resources

                         2, Dynamic routing needs information transmission , So it's easier to use , Cause safety problems

                         3, The routing of dynamic routing is calculated by algorithm , Not necessarily the best path , There may even be a loop .

Basic configuration of static routing :
Method 1 :[rlip route—static 192.168.3.0 24 192.168.2.2 —- You need to recursively find the interface
Method 2 : [1lip route—static 192.168.3.02 4 GigabitEthernet 0/0/1- The agent needs to be activated ARP
             [r2—GigabitEtherneto/O/0larp—proxy enable — The activation agent ARP —-— ARP A kind of , After activation ,                The router will check the received ARP Request package , be based on ARP Requested P Address view local routing table , If the local route                   Can be up to , Will pretend to be the other party's P Address reply ARP The reply . To his own MAC Address reply , after , The data is sent to the route                 On the device , The router forwards .
Method 3 :[r1]ip route—static 192.168.3.0 24 GigabitEthernet 0/0/1 192.168.2.2— Recursive search is not required             look for
Method four : [rl]ip route—static 192.168.4.0 24 192.168.3.2—-— Write down two jumps , You need to look up recursively

Extended configuration of static routing :
1, Load balancing —— When a router accesses the same target with multiple paths with similar overhead , You can make the flow
After splitting the quantity, go from multiple paths at the same time , Play the effect of superimposing bandwidth .
2, Manual summary —— When a router can access multiple consecutive subnets , If they all pass the same next jump , be
These network segments can be summarized and calculated , Directly write a static route to the summary network segment . You can reduce
Reduce the number of routing table entries , Improve forwarding efficiency .
3, The route is black - In the river , The knowledge fruit contains the same segment that does not exist in the middle process of the same name , It may cause traffic
Go without return , Waste link resources .
Reasonable division and aggregation can reduce the generation of routing black holes
4, Default route —— A route that does not limit the destination . When looking up the table , If all routes do not match , Will
Match default route .
[r1]ip route-static 0.0.0.0 0 12.0.0.2
5, Empty interface routing —— Prevent routing black holes and default routes from meeting and leaving the ring . Configure a black hole router
The route that reaches the summary network segment and points to the empty interface .
1, NUL0 If the outgoing interface of a route entry points to an empty interface , Then match to this route information
Datagrams will be discarded
2, Matching principle of routing table —— The longest match principle ( The principle of exact match )

[r1]ip route-static 192.168.0.0 2 NULL 0
6, Floating static routing —— By modifying the default priority of static routing , Achieve the effect of backup
[r2]ip route-static 192.168.0.0 22 21.0.0.1 preference 61