Router BASICS (1)

1. Router Overview

A router is a network device that connects multiple networks or CIDR blocks. It can translate data between different networks or CIDR blocks ", so that they can "read" each other's data to form a larger network. It is not used for devices of the same network segment, but for devices of different network segments or between different networks. It is an Internet device. The reason why a vro can translate between different networks is that it is no longer a pure hardware device, but a soft and hard-structure device with rich routing protocols, for example, RIP, OSPF, OSPF, and IPV6. These routing protocols are used to achieve mutual "Understanding" between different network segments or networks ".

Vro has two typical functions: Data tunnel and control. The data channel functions include forwarding decision, backplane forwarding, and output link scheduling, which are generally completed by specific hardware. The control functions are generally implemented by software, it includes information exchange with neighboring routers, system configuration, and system management.

A vro can determine the network address and select a path. It can establish flexible connections in a multi-Network Interconnection Environment and connect subnets using different data groups and media access methods. A vro only accepts information from the source station or other routers. It is an interconnected device at the network layer. It does not care about the hardware devices used by each subnet, but must run software consistent with the network layer protocol. Vrouters are divided into local routers and remote routers. Local routers are directly connected through transmission media such as optical fiber cables, coaxial cables, and twisted pair wires. Are remote routers directly connected through the above transmission media, instead, remote connections are made through other networks, such as telephone networks and cable TV networks.

Among the many LAN access methods, vro access to the Internet is the most common method. The biggest advantage of using a vro network is that each subnet remains independent, and each subnet can adopt a different topology, transmission medium, and network protocol. The network structure is hierarchical, other routers have VLAN management functions. By connecting a vro to the Internet, you can completely block the company's internal network and act as a firewall. Therefore, using a vro to access the Internet can also ensure the security of the Intranet.
Note: Although vrouters and other network devices have many software protocols and OS systems, they are still hardware devices, network devices, such as hubs and switches, are not afraid of attacks ). In addition, a vro has an independent public IP address. When a LAN accesses the Internet through a router, only the public IP address of the router is displayed on the Internet, while the LAN user uses the lan ip address, it does not belong to the same network, so it plays a protection role.

In essence, a vro is also a computer, and its operating system is loaded into the memory from the ROM during computer boot. With the increasing popularity of Internet and enterprise networks, vrouters are also widely used. Currently, there are many vro brands on the market, Cisco is the most authoritative vro technology. In a sense, it is the name of a vro, so when people talk about the name of a router, they will think of the name Cisco. Cisco routers not only have a complete product line, but also have Cisco 1600/1700 series at the low end, Cisco 2500/2600/3600 series at the middle end, and Cisco 7200/12000 series at the high end), and their technology is also the most advanced, guide the entire market. However, Huawei, after more than a decade of development, has become very powerful. To some extent, it has almost become one of Cisco's most competitive companies. to suppress the development of Huawei, not long ago, he was still involved in an infringement lawsuit against Huawei.

The configuration file of the newly purchased vro is empty. The administrator must edit the configuration file of the vro and write it into the nvram of the vro ). In this way, the vro will perform corresponding operations according to the configuration file at the next startup.

The main task of a router is to find an optimal transmission path for each data frame passing through the router and transmit the data to the destination site effectively. It can be seen that the routing algorithm is the key to selecting the optimal path. To do this, the route Table Routing Table is stored in the vro for route selection. The path table contains the subnet flag information, the number of online routers, and the name of the next router. The path table can be set by the system administrator or dynamically modified by the system. It can be automatically adjusted by the router or controlled by the host. Two concepts about IP addresses are involved in a vro: static path table and Dynamic Path table. The system administrator sets a fixed route table in advance, which is called a static route table. Generally, it is set in advance according to the network configuration during system installation, it will not change as the network structure changes in the future. Dynamic) the route table is automatically adjusted by the router according to the running status of the network system. The router selects the Routing Protocol) to automatically learn and remember the network running status, and automatically calculate the optimal path for data transmission as needed.

Ii. Main Functions of routers

The main function of a vro is the role of "routing". In general, it is the role of "Wizard", which is mainly used to specify a direction for data packet forwarding. However, to be subdivided, the router's "routing" function can be subdivided into the following aspects:

1) receive data packets sent from nodes on the Internet, and then forward the data packets to the target node based on the source address and destination address in the data packet against the route table in the cache, this is the most important and basic routing role of the router I mentioned above.

2) select the most reasonable route for inter-Internet communication. This function is actually an extension of the preceding routing function. If several networks are connected through their respective routers, users in one network must send access requests to users in another network, the router analyzes the source address of the request and the network ID number in the destination node address of the request, and finds out an optimal, economical, and fastest communication path. Just as we usually go to a strange place and don't know the best way to go to the destination point, we have to find a wizard. This Wizard will tell us the best shortcut, because he is familiar with every route, the vro mentioned here is equivalent to the "Wizard" here ".

3) split and package data packets. This function is also a subsidiary of the routing function. Sometimes, in the packet forwarding process, if the packet is too large due to factors such as network bandwidth, it is easy to cause network congestion, in this case, the vro splits large data packets into small data packets based on the bandwidth of the peer network. After arriving at the vro of the target network, the vro of the destination network then packs the split data into a packet of the original size, obtains the MAC address of the destination node based on the forwarding information of the source network router, and sends it to the node of the local network.

4) connections between different protocol networks. At present, most medium and high-end routers often have the functions supported by multiple communication protocols, which can connect two different communication protocol networks. For example, the common communication protocol used by the Windows NT operating platform is mainly TCP/IP, but if it is a NetWare system, the communication protocol used is IPX/SPX, there are also some special protocol CIDR blocks, which must be connected by routers supporting these protocols.

5) At present, many vrouters have network-managed routers with firewall functions that can be configured with independent IP addresses. It can provide basic firewall functions, that is, it can shield internal network IP addresses, you can freely set IP addresses and communication port filters to make the network more secure.