Catalog

One 、

ARP Attack principle

Two 、

Introduction to transport layer protocol

TCP Why is the Agreement three handshakes instead of two ？

One 、

ARP Attack principle

• Deceive all other computers
• Spoofing the attacked computer

ARP Spoof gateway

ARP Spoofing the host

Manage the network through Longhorn network monitoring machine software

• Set the monitoring range · Network management
• Verification effect

ARP Fault handling

Demand analysis

• Benet The company suddenly cannot access the Internet normally
• Discover the host ARP The number of gateways in the cache table MAC The address is incorrect

Two 、

Introduction to transport layer protocol

TCP/IP Transport layer protocol of protocol family

• TCP (Transmission Control Protocol )

     ◆ Transmission control protocol

• UDP (User Datagram Protocol )

     ◆ User datagram protocol

TCP Why is the Agreement three handshakes instead of two ？

reason 1： It is mainly to prevent the failed connection request message from being suddenly transmitted to the server , This leads to unnecessary errors and waste of resources .

If you use two handshakes to establish a connection , Let's say there's a scenario , The first request sent by the client connects and is not lost , Just because I've been on the Internet for too long , because TCP The client of has not received the confirmation message , Thought the server didn't receive , Send this message to the server again , After that, the client and the server complete the connection through two handshakes , To transmit data , Then close the connection . The connection request that was held before this time , Because the network is unobstructed , Reached the server , This newspaper text should be invalid , however , The two handshake mechanism will allow the client and the server to establish a connection again , This will lead to unnecessary mistakes and waste of resources .

If three handshakes are used , Even if the failed message was transmitted , The server receives the invalid message and replies the confirmation message , But the client will not issue a confirmation again . Because the server can't receive confirmation , Just know that the client didn't request a connection

TCP And UDP The difference between ？

TCP and UDP The difference between

(1)TCP It's a reliable transmission ,UDP It's an unreliable transmission ;

(2)TCP Connection oriented ,UDP There is no connection ;

(3)TCP Transmit data in order ,UDP The order of data is not guaranteed ;

(4)TCP Do not save data boundaries ,UDP Preserve data boundaries ;

(5)TCP The transmission speed is relative UDP slower ;

(6)TCP There are flow control and congestion control ,UDP No, ;

(７)TCP It's a heavyweight agreement ,UDP It's a lightweight protocol ;

(８)TCP The first part is long ２０ byte ,UDP The head is short ８ word

TCP The meaning of each state of three handshakes ∶
LISTEN: Listening from far away TCP Connection request for port
SYN_SENT: Wait for the matching connection request after sending the connection
SYN_RECEIVED : Wait for confirmation after receiving and sending a connection request
ESTABLISHED: Represents an open connection , Can transmit data
FIN_WAIT1: Waiting for remote TCP Connection interrupt request for
FIN_WAIT2: From remote TCP Wait for connection interrupt request
CLOSE_WAIT: Waiting for the connection interrupt request from the local user
CLOSING: Waiting for remote TCP Confirmation of interruption .
LAST_ACK: Wait for the confirmation of the interrupt request
TIME_WAIT: Wait enough time to make sure that the remote TCP Received connection interruption request confirmation
CLOSED : There is no connected state .

Summary ：

• TCP Is a reliable connection oriented protocol
• TCP It takes three handshakes to establish a connection
• TCP It takes four waves to disconnect
• UDP Is an unreliable connectionless protocol