Hub,bridge,switch and router的区别

首先说HUB,也就是集线器。它的作用可以简单的理解为将一些机器连接起来组成一个局域网。而交换机（又名交换式集线器）作用与集线器大体相同。但是两者在性能上有区别：集线器采用的式共享带宽的工作方式，而交换机是独享带宽。这样在机器很多或数据量很大时，两者将会有比较明显的。而路由器与以上两者有明显区别，它的作用在于连接不同的网段并且找到网络中数据传输最合适的路径，可以说一般情况下个人用户需求不大。路由器是产生于交换机之后，就像交换机产生于集线器之后，所以路由器与交换机也有一定联系，并不是完全独立的两种设备。路由器主要克服了交换机不能路由转发数据包的不足。

Hub

A Hub is the simplest of these devices. In general, a hub is the central part of a wheel where the spokes come together. Hubs cannot filter data so data packets are sent to all connected devices/computers and do not have intelligence to find out best path for data packets. This leads to inefficiencies and wastage.

As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a token ring), and a connection to a line. Hubs are used on small networks where data transmission is not very high.

集线器就是最简单的设备，但是不能过滤数据，并且是共享带宽，所以在这个局域网内，所有设备都会接受到hub的数据。一般用于数据交换不大的情况下。
Bridge

In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol. Having a single incoming and outgoing port and filters traffic on the LAN by looking at the MAC address, bridge is more complex than hub. Bridge looks at the destination of the packet before forwarding unlike a hub. It restricts transmission on other LAN segment if destination is not found.

A bridge works at the data-link (physical network) level of a network, copying a data frame from one network to the next network along the communications path.

就是网桥，在一个可以访问的网络中，从这个机器可以连上另外的网络，网桥比集线器复杂可以重定向数据，工作在数据链路层。
Switch

A switch when compared to bridge has multiple ports. Switches can perform error checking before forwarding data, which are very efficient by not forwarding packets that error-end out or forwarding good packets selectively to correct devices only.

Switches can support both layer 2 (based on MAC Address) and layer 3 (Based on IP address) depending on the type of switch. Usually large networks use switches instead of hubs to connect computers within the same subnet.

与网桥相比，交换机具有多个端口。 交换机可以在转发数据之前执行错误检查，这通过不转发错误结束的分组或仅将正确分组选择性地转发到正确的设备来非常有效。
交换机可以支持第2层（基于MAC地址）和第3层（基于IP地址），具体取决于交换机的类型。 通常大型网络使用交换机而不是集线器连接同一子网内的计算机。
Router

A router, like a switch forwards packets based on address. Usually, routers use the IP address to forward packets, which allows the network to go across different protocols. Routers forward packets based on software while a switch (Layer 3 for example) forwards using hardware called ASIC (Application Specific Integrated Circuits). Routers support different WAN technologies but switches do not.

Besides, wireless routers have access point built in. The most common home use for routers is to share a broadband internet connection. As the router has a public IP address which is shared with the network, when data comes through the router, it is forwarded to the correct computer.

路由器，像交换机根据地址转发数据包。 通常，路由器使用IP地址转发数据包，这允许网络跨越不同的协议。 路由器基于软件转发分组，而交换机（例如，层3）使用称为ASIC（专用集成电路）的硬件转发。 路由器支持不同的WAN技术，但交换机不支持。
此外，无线路由器具有内置的接入点。路由器最常见的家庭使用是共享宽带互联网连接。 由于路由器具有与网络共享的公共IP地址，当数据通过路由器时，它被转发到正确的计算机。

Repeaters

Repeaters are built into the hubs or switches. Repeaters clean, amplify and resend the signals that have been weakened due to long cables traveling large distances.

中继器，在集线器和交换机中，主要是净化，放大和重新发送由于长距离电缆传输而削弱的信号。