Router principles, categories, and purchasing

We have a comprehensive understanding of the basic aspects of the router in the previous article. This article will continue to introduce other aspects of the router. First, we should introduce the working principle of the router. Only after fully understanding the working principle of the router can we correctly understand the main role of the router.

I. Working Principle of routers

We know that routers are used to connect different network segments or networks. In a LAN, if you do not need to communicate with the external network, the workstations in the internal network can identify other nodes, you can use a vswitch to send messages. You cannot use a vro to remember the MAC addresses of each node in the LAN. The router identifies different networks by identifying the network ID numbers of different networks. Therefore, to ensure successful routing, each network must have a unique network ID. To identify another network, the router must first identify the network ID of the vro IP address of the peer network to see if it is consistent with the network ID number in the destination node address. If it is, of course, sent to the router of this network, after receiving the packet from the source network, the router of the receiving Network, identify the node to which the message is sent based on the host ID in the IP address of the destination node, and then send it directly.

To better illustrate the working principle of the router, we assume that there is such a simple network. Assume that four terminal devices are connected together in the same CIDR block, and the IP addresses of each device in this CIDR block are assumed to be: a1, A2, A3, and A4. A Router connected to this CIDR block is used to connect to other CIDR blocks. the IP address of the port connecting the router to CIDR Block A is A5. Similarly, when a router connects to another CIDR block of B, the network ID of This CIDR block is "B", and the IP addresses of the other wks connected to the B CIDR block are set: b1, B2, B3, B4. We set the IP address of the router port connecting to the B network segment to B5, as shown in structure 1.

Figure 1

There are two different CIDR blocks in such A simple network at the same time. If A1 users in CIDR Block A want to send data to B2 users in CIDR Block B, with a vro, it is very simple.
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First, A1 prepares the sent data and sent packets, and broadcasts the data to all nodes in the same CIDR Block through the hub or switch in the form of data frames, because the vswitch cannot recognize this address, it also adopts the broadcast mode). After listening to the data frame sent by A1, analyze the IP address information of the target node (the router always needs to analyze the IP address after obtaining the data packet ). If it is known that it is not the current segment, it receives the data frame and further analyzes the route table to find that the network ID of the receiving node is the same as that of port B5, at this time, the A5 port of the router sends the data frame directly to the B5 port of the router. Port B5 then determines the destination node as B2 Based on the host ID in the destination node IP address information in the data frame, and then sends the data to node B2. Such a complete data frame routing and forwarding process is completed, and the data is successfully delivered to the target node correctly.

Of course, in fact, a network like above is very simple, and the functions of the router cannot be fundamentally reflected. Generally, a network will connect to multiple other network segments or networks at the same time, as shown in figure 2, A, B, C, and D networks are connected through routers.

Figure 2

Now let's take a look at how vrouters play their routing and data forwarding roles in the network environment 2. We also need to assume that the IP Address Allocation of each network user is not mentioned much, as shown in figure 2. Assume that A user A1 in Network A sends A request signal to the C3 user in Network C as follows:

Step 1: User A1 sends the target user C3 address C3 together with data information to all nodes in the same network in the form of data frames through a hub or switch in the form of broadcast, when port A5 of the vroa5 listens to this address, the analysis shows that the destination node is not in this network segment. If the destination node needs to be routed and forwarded, the data frame is received.

Step 2: After receiving data frames of user A1, port A5 of the router extracts the IP address of the target user C3 from the header and calculates the optimal route table for user C3. Since the analysis shows that the C3 network ID number is the same as the C5 network ID number of the vroc5, direct transmission from the A5 port of the vroa5 to the C5 port of the vro should be the best way to transmit signals.

Step 2: The C5 port of the vroc5 fetches the IP address of the target user C3 again, and finds the host ID in the IP address of C3. If there is a switch in the network, it can be sent to the switch first, the switch identifies the specific network node Location Based on the MAC address table. If there is no switch device, the data frame is directly sent to the user C3 Based on the host ID in the IP address, this complete data communication and forwarding process has also been completed.

It can be seen from the above that no matter how complicated the network is, the router actually works in such a few steps, so the principle of the entire router is almost the same. Of course, the actual network is much more complex than the steps shown in 2, and the actual steps are not as simple as above, but the general process is like this.

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Ii. Classification of vrouters

Nowadays, to meet various application needs, there have also been various vrouters. Next we will simply make a comprehensive classification of the entire router market.

　　1. By performance grade

Any product seems to have a default classification standard, which is generally referred to as high, medium, and low. Vrouters can also be divided into high, medium, and low-end routers, but the division of the manufacturers is not completely consistent. Generally, a router with a backplane switching capability greater than 40 Gbps is called a high-end router. The backplane switching capability is between 25 Gbps and ~ A vro between 40 Gbps is called a mid-range router. A vro between 40 Gbps and 25 Gbps is a low-end router. Of course, this is only a macro classification standard. In fact, the classification of router grades is not only based on the backboard bandwidth, but also has a comprehensive indicator. Take the Cisco company with the largest market share as an example. The 12000 series are high-end routers, and The 7500 or lower series routers are low-end routers. The left, middle, and right pictures of Figure 3 are Cisco's high, medium, and low router products.

Figure 3

　　2. By Structure

In terms of structure, routers can be divided into modular and non-modular structures. A modular structure can be used to flexibly configure routers to meet the increasing business needs of enterprises. A non-modular structure can only provide fixed ports. High-end routers are generally modular, and low-end routers are non-modular. The left and right figures shown in Figure 4 are non-modular and modular router products.

Figure 4

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3. functional division

In terms of functions, routers can be divided into core layer (backbone level) routers, distribution layer (enterprise level) routers and access layer (access level) routers.

· Backbone router: a backbone router is a key device for enterprise-level network interconnection. It has a large amount of data and is very important. The basic performance requirements for backbone routers are high speed and high reliability. To achieve high reliability, network systems generally use traditional redundancy technologies such as hot backup, dual-power supply, and dual-data channels, so that the reliability of backbone routers is generally not a problem. The bottle of a backbone router looks for a vro in the forwarding table. It usually puts some destination ports with High Access frequency into the Cache to improve the routing search efficiency.

· Enterprise-level Routers: enterprise-level routers or campus routers connect to many terminal systems with many connection objects, but the system is relatively simple and the data traffic is small, the requirement for such vrouters is to achieve as many endpoints as possible in a way that is as cheap as possible, and also to support different service quality. Because the network system connected by the router can divide the machine into multiple collision domains, the size of a network can be easily controlled. In addition, a vro can support a certain level of service, at least allowing the network to be divided into multiple priority levels. Of course, the cost per port of the router is more expensive. before using the router, you must perform a lot of configuration work. Therefore, the success or failure of enterprise-level routers lies in whether a large number of ports can be provided, the cost per port is low, whether it is easy to configure, whether it supports QoS, whether it supports broadcast, multicast, and many other functions.

· Access-level Routers: Access-level routers are mainly used to connect small enterprise customers in the home or ISP. In the near future, the Access Router will have to support many heterogeneous and high-speed ports and run multiple protocols on each port.
 
　　5. Division from applications

In terms of functions, routers can be divided into general-purpose routers and dedicated routers. Generally, all vrouters are generic routers. A vro is usually used to optimize router interfaces and hardware for specific functions. For example, the Access Server is used to access dial-up users, and the PSTN interface and signaling capability are enhanced. The VPN Router is used to provide routes for remote VPN access users, it must have specific capabilities in terms of tunneling processing capabilities and hardware encryption, while broadband access routers emphasize interface bandwidth and types.

　　6. Divide by network location

If the router is divided by the Network Location of the router, the router is usually divided into two types: "border router" and "intermediate node Router. It is obvious that "VBR" is at the edge of the network and used for connection between different network routers, while "intermediate node Router" is in the middle of the network and is usually used to connect different networks, it serves as a bridge for data forwarding. Because their respective network locations are different, their main performance also has a corresponding focus, such as intermediate node routers because they need to face a variety of networks. How can we identify nodes in these networks? It relies on the MAC address memory function of these intermediate node routers. For the above reason, when selecting an intermediate node router, you need to pay more attention to the MAC address memory function, that is, you need to select a router with a larger cache and a better MAC address memory. However, because the VBR may accept data from many different network routers at the same time, this requires that the bandwidth of the VBR be wide enough, of course, this depends on the network environment of the VBR. Although