ARP protocol
Address Resolution Protocol, ARP (Address Resolution Protocol), is a TCP/IP protocol that obtains physical addresses based on IP addresses. When the host sends information, it broadcasts the ARP request containing the target IP address to all hosts on the local area network, and receives the return message to determine the physical address of the target; after receiving the return message, save the IP address and physical address to the machine The ARP cache is kept for a certain period of time, and the ARP cache is directly queried when requested next time to save resources.
Usually when we are doing campus network operation and maintenance, our school teaching area uses the Portal authentication mode to access the Internet. Sometimes because the authentication interface does not pop up or there is a link problem, it will not go online. We generally check the network problem. Looking at the problem of the link layer, we will think of the logical link control sublayer of the data link layer, which is what we call the mac sublayer. I took my own computer as an example. We chose Ruijie Full Gigabit Security & Intelligence Access Switch (S2928G-E V3) By Ruijie Networks
We enter in privileged mode
show mac-address-table interface gigabitEthernet 0/1
Because the ip address is at the network layer, we have to select the access device at layer 3 and enter it in the privileged mode
show arp 54bf.647b.xxxx
Then the corresponding network address can be inquired, which can help us locate the fault conveniently.