Hubs, L2 switches, routers, and L3 Switches

Hub: previously dedicated to 10 m shared Ethernet, which is rarely used. It only works on the physical layer and uses half-duplex communication between the port and the host. Generally, no matter whether the physical connection is bus or star, its logical connections are bus-type. As long as one of the hosts sends information, the hub will copy the information to all other port hosts. The Hub is also called a multi-port repeater, all hosts connected to a hub share a conflict domain. The so-called conflict domain is not intended to be sent to all hosts, but after the hub, all ports will receive information, that is, share a conflict domain, if messages are sent from other hosts, conflicts and congestion may occur. A hub can be used as a repeater for long-distance network relay, but this will lead to the expansion of the conflict domain. This problem is also discussed below.
 
L2 Switch: A L2 Switch is used for a large number of M switched Ethernet networks. It works on the data link layer and has a Mac list. It communicates Based on port ing and can simultaneously implement multi-channel communication with exclusive bandwidth without affecting each other. Full-duplex communication is used between the port and the host. The L2 Switch has the role of dividing the conflict domain, for example:

There are four conflict domains. If the intermediate device is a hub, It is a conflict domain.
 
Vro and layer-3 vswitch: The vro has the function of dividing the broadcast domain and the conflict domain. Each port should belong to a different broadcast domain. Of course, single-arm routing may also occur, that is, a route Ethernet port is divided into two sub-logical interfaces to divide the broadcast domain. The broadcast domain is consciously broadcast to all hosts in this network. There is no ARP concept for a L2 Switch, just like in a LAN that does not communicate with the outside world, it is sufficient to use a L2 Switch to communicate with hosts in the LAN Using the Mac list of the switch. Once two different subnet hosts need to communicate with each other, or the LAN host wants to connect to the WAN, or the hosts with different VLANs need to communicate with each other, an intermediate gateway is required for two different networks, generally, you can use a vro or a layer-3 Switch to achieve this purpose. However, you need to know that a layer-3 Switch cannot interconnect the LAN or wide area network, because the layer-3 switch does not have so many types of ports, although the number of ports is much higher than that of vrouters. For VLAN communication, the two vro ports should be connected to different VLANs. to expand the number of hosts, the two vro ports should be connected to the two-layer vswitch at the outer side of the vro port. For layer-3 vswitches, because there are many Ethernet ports, all hosts are directly connected to the port and divided into a VLAN (not based on the physical location). Note that a port can belong to different VLANs, a VLAN can also contain multiple ports.
 
 
Collision slot time: This concept appears in shared Ethernet and is an important parameter for determining how many devices can share the network. The collision slot ensures that when a conflict occurs, it will be detected within the minimum frame transmission time. When the Ethernet speed is 10 M and M, the collision slot time is the minimum transmission time of the Ethernet frame, that is, 64 * 8bit = 512bit. When the speed is 1 GB, the collision slot time is 4096bit. If a conflict occurs, it will be detected within the first collision slot time. The collision slot time includes the signal transmission time along the cable and hub. It is used to define the maximum length of the network cable and the number of hubs that can be used by the Ethernet segment of the shared media. The larger the number of hubs, the greater the latency, the message may be sent to both sides at the same time. However, the long distance delay leads to no detection. This is equivalent to a conflict that occurs when the hub expands the conflict domain, that is, CSMA/CD does not work here.
 
 
For latency, the cable The transmission rate of 100 Mb/s refers to the rate that the physical layer can reach, that is, more than 12 Mb/s. The actual transmission rate refers to the actual data rate, the effective usage of all the control information at each layer should be removed, so the limit value is generally not reached. Sometimes it is very difficult to transmit data to each other within the LAN to reach 10 MB.