Doubts
1, load balancing to achieve understanding
https://juejin.im/entry/5af135416fb9a07ab77427b5
2: DNS IP + port is equivalent to
A Domain Name System (DNS) corresponds to the IP + port numbers, IP and different port numbers may correspond to a different DNS, which can implement a host deploy multiple sites, but the port number is encapsulated in the transport layer TCP / UDP protocol, the network layer It will be put on an IP address.
Principle: The Domain Name System to find the corresponding on the corresponding server applications based on domain, different application processes corresponds to a different port number, so the DNS corresponds to the IP + port;
communication between different hosts is actually on the corresponding host communication between different processes, which is to be reflected at the transport layer, so the port number is encapsulated in a TCP / UDP; the
object is to find the corresponding network layer host, an IP address is encapsulated in the network layer, the data generated IP reported.
3: switches, bridges and other corresponding device is present in the last two LAN (the physical layer and the data link layer), and therefore also referred to as the working device in the data link layer
Principle: When the data is not required when going through a router, only the internal LAN transmission, implement LAN interconnection between the various devices, you do not need the use of IP addresses (but before still need to check the routing table to determine the two hosts are on the same LAN, Try to find the MAC address corresponding to the IP address of the destination host by the ARP), with the MAC address on the list, then switches, bridges, and other equipment transfers data to the destination host through a data link layer.
ARP is to resolve the IP address and hardware address of the host or router on the same LAN mapping problem
Internal bridge forwarding record is different from the host Mac address and bridge the corresponding forwarding interface, according to which will be able to find the corresponding device.
Note that in the process of transmission, even useless to IP, TCP / UDP protocol, etc., but it is also present, the destination host, it will be up protocol analysis. TCP or UDP is also a need to ensure that data transmission, not to find the destination host inter-process communication and confuse.
That, alone to complete the communication between each other LAN hosts, in fact, does not need to use the network layer
Note: Hubs operate at the physical layer, it is just simply forward each interface bits, collision detection is not performed.
Whether the two host communication network segment needs a router? : Https://www.zhihu.com/question/41496681
4, the communication between the two QQ
Communication between the two QQ, according to the distance, whether or not in the same network segment, can be divided into three forms
https://www.zhihu.com/question/310020853
1, QQ server transfer
2, transit router 
3, the relay switch
A (Bob) -> Switch -> B (Mel)
Try shortest route priority (3), if not, try suboptimal route (2), if not OK, and finally use the straw (1).
More Reference: https://blog.csdn.net/realxie/article/details/7270119
when you log QQ game server, the server will keep your reserved IP address and port number information, and your friend's QQ carried out the process list display, and then the two processes can communicate.
5: the difference between IP and Mac address
https://blog.csdn.net/yang_best/article/details/41643589
6: the difference between LAN, WAN and the Internet
https://www.zhihu.com/question/51295773
If the LAN is creek, brook many converging on big mainstream, such as the Yangtze, Yellow River is the wide area network, and then into the sea, the ocean is the Internet.
WAN does not mean that internet