Q1: Where is the difference between the bridge, HUB, routers, and switches? The first layer exchange: The bottom of the network is the repeater Repeater. It works in the physical layer. It is the two-way signal. The usual effect is that the model is not too attenuated and deformed when the line is longer. There are no differences in some delays, and there is no difference between the direct cable. Layer 2 exchange: Britge and HUB and switch Switcher work in the data link layer, but the two mechanisms are different. Strictly speaking, although HUB connects multiple hosts, it is not a switching device. It faces Ethernet frames, its work is the frame of Ethernet received in a port, broadcast to all ports (also It is possible to correct the chain layer. This is, the work mechanism of its repeater is the same, but the hierarchy of the work is different. In this way, only Hub's connection can only be a local area network segment. And the import and export of HUB is different. Switch Switcher is also connected to multiple computers, but it records the MAC address of the host corresponding to each port, so that its forwarding is not a broadcast form, but it is selected. Only the connection of the switch can only be a local area network segment. And the import and export of Switcher is different. For portions, each port can only correspond to one MAC address, and the MAC address in other cases corresponds to the exit. Bridge also works in the data link layer, its role is also connected to the two network segments, and the forwarding of Ethernet frames, but its forwarding mechanism is not broadcast, and there is a switch in the interior, there is a table to make a selection forward. Different, Bridge is different from the entrance and export. It can be understood that the two are basically the same on the hardware, and the difference is that each inlet of the Bridge can correspond to multiple MAC addresses. The third floor exchange: this is the router, it is an IP address, this everyone is very familiar. I think that the high-level switching device can be used in the underlying exchange device, for example, you can use the HUB to connect to two machines far away, only use of the electrical signal enlargement. You can also use the router as a HUB or switch, just connect some hosts as a local area network. Q2: If a destination MAC address of an Ether web frame is not a native, the NIC driver should still be charged to the driver buffer, then discarded by hardware? ? If the network port is set to a mixed mode, is it a network card to receive, or hand it over to the link layer? ? Change mixed mode and normal mode, what is different? NIC processing can be optimized, and all Ethernet frames are not processed. This feature is called Onboard Address Reconition, only the MAC address is handed over to the upper layer processing, which is normal mode. The so-called hybrid mode Promiscuous mode is to close this optimization function, as long as all received packages are processed. Q3: How is the so-called modification of the MAC address? This problem has not been studied, but there are two possibilities. A, the MAC address of the network card is modified. For example, the MAC address is written on the NIC's EPROM, and the driver provides the driver to modify the interface using IOCTRL. If this is the case, after modifying the MAC address above, if you change the machine, the MAC address is still modified. Some network cards running under DOS do support this way of modification.
