Network engineering: Communication between 2.1.ARP protocol and PC

ARP protocol features: by parsing Network Layer IPV4 Address to find a network transport protocol for the Data Link layer MAC address

ARP Protocol Format

Table format with ARP protocol per unit

1,the normal communication between PC principle one ( both pc can access each other )

① requirements:1.1.1.2 and 1.1.1.3 Normal communication ( native No other device ARP Information )

1) result: Xiaoming correctly put his MAC into the topic and submit it back ( Communication Success )

The final request agreement is as follows:

The final answer protocol is as follows:

The final 1.1.1.2 point ARP table is as follows

Host	IP Address	MAC Address
A	1.1.1.2	0c:3e ...
B	1.1.1.3	Qw:31 ...

1. Proxy ARP

(1) When broadcasting, received and answered by other devices of the non-requesting address device in the link

2. Reverse ARP

(1) DHCP server, thePC will automatically receive a response from DHCP when connected to the network

① response information includes : IP + Mask + Gateway + DNS

3, unreasonable ARP ( next )

① If there is a 1.1.1.2 issue such as an ARP Request

1) result : 1.1.1.3 immediately break the net

② If there is a software, send a whole network segment such a request

1) Result: The entire network segment is immediately disconnected from the network

1. HSRP hot standby router protocol

(1) according to the known when the line 1 port is damaged, the ARP is sent from Route 2 and Route 3 Protocol

(2) ARP may proxy reply from router2 and router3 using its own table data

The HSRP protocol is configured with three multicast messages: Hello ——— Hello message notifies other routers of the HSRP priority and status information of the sending router, and the HSRP router defaults to sending a hello message every 3 seconds; Coup ———　　A coup message is sent when a standby router becomes an active router; Resign ——— when the active router is going down or when a higher-priority router sends a Hello message, the active router sends a RESIGN message.　　　　At any one time, one of the six states of the router that has the HSRP protocol configured: Initial ——— the status of HSRP when it is started, HSRP is not running, and is typically entered in this state when the configuration is changed or the port has just started. Learn ——— learning State, do not know the virtual IP, do not see the active router to send hello.　　　　Wait for the active router to send hello. The Listen ——— router has been given a virtual IP address, but it is neither an active router nor a waiting router.　　　　It listens for Hello messages from both the active router and the waiting router.　　　　Speak ——— in this state, the router periodically sends a HELLO message and actively participates in an active router or waiting for the router to run.　　　　Standby ——— when the active router fails, the router is ready to take over the packet transport function. The Active ——— router performs the package transfer function.

Network engineering: Communication between 2.1.ARP protocol and PC