1. The loop: according to the learning of switch address and the establishment algorithm of station table, there is no loop between switches. Once there is a loop, the spanning tree algorithm must be launched to block the port that generates the loop. The router routing protocol does not have this problem. There are multiple paths between routers to balance load and improve reliability.
2. load concentration: there is only one access between switches, so that information can be concentrated on a communication link and can not be dynamically allocated to balance load. The routing protocol algorithm of the router can avoid this. The OSPF routing protocol algorithm can not only generate multiple routes, but also select the best routes for different network applications.
3. broadcast control: switches can only narrow the collision domain, but not narrow the broadcast domain. The whole switched network is a large broadcast domain, and broadcast messages are dispersed to the entire switched network. The router can isolate the broadcast domain, and broadcast packets cannot be broadcast through routers.
4. subnet partition: the switch can only identify the MAC address. MAC address is physical address, and uses a flat address structure, so it can not be divided into subnets according to the MAC address. The router identifies the IP address, and the IP address is assigned by the network administrator. It is a logical address and the IP address has a hierarchical structure. It is divided into network numbers and host numbers. It can be used to divide subnets very conveniently. The main function of the router is to connect different networks.
5. security problem: Although the switch can also filter the frame according to the source MAC address, the destination MAC address and the contents in other frames, the router filters the message according to the source IP address, the destination IP address, the TCP port address and so on.