A survey of router technology

In today's information society, people's demand for data communication is increasing. As the core equipment of IP network, the technology of router has become the key technology of the current information industry.

What is a router

Routers are packet forwarding devices that work in the third layer of the OSI Reference Model-the network layer. Routers implement network interconnection by forwarding packets. Although routers can support multiple protocols (such as TCP/IP, ipx/spx, AppleTalk, etc.), most routers in China run TCP/IP protocol.

Routers typically connect two or more logical ports identified by an IP subnet or Point-to-Point protocol, with at least one physical port. The router determines the output port and the next hop address based on the network layer address in the packet and the routing table maintained within the router, and overrides the link layer packet header to implement forwarding packets.

Routers usually dynamically maintain routing tables to reflect the current network topology. Routers maintain routing tables by exchanging routing and link information with other routers on the network.

Routers are the core devices that connect IP networks.

Classification of routers

The current router classification methods are different. There is a certain correlation between the various classifications, but not exactly the same.

From the ability points, routers can be divided into high-end routers and low-end routers. The division of the manufacturers is not exactly the same. The router, which usually has a backplane switching capacity greater than 40G, is called a high-end router, and a router with a backplane switching capability below 40G is called a low-end router. Cisco, the largest market share, for example, the 12000 series for high-end routers, 7500 of the following series routers for low-end routers.

From the point of view of structure, the routers can be divided into modular structure and non modular structure. In general, high-end routers are modular structures, and low-end routers are not modular.

From the network location division, routers can be divided into core routers and access routers. The core routers are located in the network center, usually using high-end routers. Fast packet switching capabilities and high-speed network interfaces are required, usually modular structures. The access router is located at the edge of the network and typically uses low-end routers. Requires relatively low speed ports and strong access control capabilities.

From the functional points, routers can be divided into common routers and dedicated routers. Generally speaking, the router is a generic router. A dedicated router typically optimizes router interfaces, hardware, and so on to implement a particular function. For example, the access server is used as an access dial-up user, enhances the PSTN interface and the signaling ability, the VPN router enhances the tunnel processing ability as well as the hardware encryption, the broadband access router emphasizes the broadband interface quantity and the kind.

From the performance points, routers can be divided into wire-speed routers and non-wire-speed routers. Typically, a wire-speed router is a high-end router that forwards packets at a media rate, and the low-end router is not a wire-speed router. But some new broadband access routers also have a wired speed forwarding capability.

There are many ways to classify routers, and with the development of router technology, more and more classification methods may appear.

Router Features

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Implementation of IP, TCP, UDP, ICMP and other Internet protocols.

A network that is connected to two or more packet exchanges. For each connected network, implement the functionality required by the network. These features include:

IP packets are encapsulated into link-layer frames or removed from the link-layer frame.

Send or receive IP datagrams according to the maximum packet size supported by the network. The size is the network Maximum transmission Unit (MTU).

Converts an IP address to and from the link-layer address of the corresponding network. For example, the IP address is converted to an Ethernet hardware address.

Implement network-supported flow control and error indication.

Receive and forward packets, implement buffer management, congestion control and fairness processing in the transceiver process.

Identify errors when errors occur and generate ICMP errors and necessary error messages.

Discards a data packet with a live time (TTL) field of 0.

Fragment the packet if necessary.

Select the next hop destination for each IP packet according to the routing table information.

Supports at least one internal Gateway Protocol (IGP) to Exchange routing information and accessibility information with routers in the same autonomous domain. Supports external gateway protocol (exterior gateway PROTOCOL,EGP) to Exchange topology information with other autonomous domains.

Provides network management and system support mechanisms, including storage/upload configuration, diagnostics, upgrades, status reports, exception reporting, and control.