1 identical IP

a) Within the same network segment

It's going to happen IP Address conflict . Under specific circumstances, two hosts can use the same IP Address of the . But if the two hosts are in the same network , Most of the time , The connectivity of both or one of them will be destroyed . For example , Visit a page , The message may be sent in many segments , If a host receives some of these clips , And another host receives the rest , In this way, neither host can get the correct response . The main reason is when the data reaches the network device , In the face of the same IP Two hosts of , Either refuse to forward or transmit , Or send it randomly to one of the hosts . thus , The agreement was broken .

b) In different networks

Does not affect the normal service of the agreement .

2 identical MAC

a) Not in the same layer 2 network

It doesn't make any difference , because MAC It doesn't cross the gateway to another network segment .

b) In the same layer 2 network

Assume A、B、C For the host ,MAC The address is MAC1、MAC1、MAC3 .

  • Scene one : Connect through hub
    ①A or B And C signal communication
    There is no effect
    ②A And B signal communication
    Between them IP The packet arrives at the network card , Encapsulated in Ethernet frames , Purpose 、 Source MAC All for MACa, And then we can get to each other , So it doesn't affect .

  • Scene two : Connect through a switch
    ① A or B And C signal communication
    A And B If one side is silent , That is, there is no Internet activity ,A or B And C There should be no problem with your communication , But once A and B At the same time, there are network traffic generation , Exchange opportunities are emerging ARP When mapping tables , Because alternate binding MACa Address and A、B Port number , It should have been sent to A The traffic may be sent to B 了 , and B Of IP Because of the purpose IP Not for yourself , So it can cause unpredictable communication barriers .
    ② A And B signal communication
    Unable to communicate , Even if A And B Both can pass ARP Find each other's MAC Address , But once the Ethernet frame reaches the switch , Exchange learning opportunities MAC, Finding the exit is the entrance , Then the Ethernet frame is returned to the original host .
    Whether scene one or scene two , Can't go through DHCP Server dynamic allocation IP Give me the same address MAC Address of the host .

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