[Network layer] router Structure

[Network layer] router Composition 1. Concept routing refers to the activity difference in moving information from the source location to the target location through a interconnected network: the main difference between routing and switching? The switch takes place at the Layer 2 (data link layer) of the OSI reference model, and the route takes place at the Layer 3, that is, the network layer. This difference determines that different control information needs to be used in the process of routing and exchange of mobile information. Therefore, the two methods to implement their respective functions are different. 2. vro1 function 1) connect to different networks 2) Select Information Transmission Lines 3) Traffic Control 3. Route table 1) the static path table is called the static path table by the system administrator. It is usually set in advance according to the network configuration during system installation, it will not change as the network structure changes in the future. 2) The Dynamic Path table is a path table automatically adjusted by the router according to the running status of the network system. The router automatically learns and remembers network running conditions based on the functions provided by the Routing selection Protocol (Routing Protocol), and automatically calculates the optimal data transmission path as needed. Iv. Router type 1) connect a vro to a small enterprise customer in the home or ISP. The Access Router does not only provide SLIP or PPP connections, but also supports VPC protocols such as PPTP and IPSec. These protocols must run on each port. Technologies such as ADSL will soon increase the available broadband for various families, which will further increase the burden on access routers. As a result of these trends, the Access Router will support many heterogeneous and high-speed ports in the future, and can run multiple protocols on each port, while also avoiding the telephone exchange network. 2) The main goal of enterprise-level routes is to achieve as many endpoints as possible in a way that is as cheap as possible, and further support for different service quality. Many existing enterprise networks are Ethernet segments connected by hubs or bridges. Although these devices are cheap, easy to install, and do not require configuration, they do not support service levels. On the contrary, networks with vrouters can divide machines into multiple collision domains and thus control the size of a network. 3) backbone routers interconnect enterprise-level networks. The requirements for it are speed and reliability, and the cost is secondary. Hardware reliability can be achieved through technologies used in the telephone exchange network, such as hot backup, dual power supply, and dual data path. The main performance bottleneck of a backbone IP router is the time it takes to find a route in the forwarding table. When a packet is received, enter the port in the forwarding table to find the destination address of the packet to determine its destination port. When the packet is shorter or the packet is sent to many destination ports, it is bound to increase the cost of Route Search. Therefore, placing some frequently accessed destination ports in the cache can improve the routing search efficiency. Whether it is an input buffer or an output buffer router, there is a bottleneck in route search. In addition to performance bottlenecks, the stability of routers is also a common concern. 4) among the three main technologies used by the core internet in the future, fiber optic and DWDM are both mature and ready-made. If there is no router corresponding to the original bandwidth provided by the existing optical fiber technology and DWDM technology, the new network infrastructure will not be able to fundamentally improve the performance, therefore, developing high-performance backbone switches/routers (vrouters) has become an urgent requirement. The Tbit router technology is still in the development experiment stage. 5) Multi-WAN router 5: Router Architecture and Composition 1) the architecture is divided into the first generation single-CPU router, the second generation single-bus master-slave CPU router, and the third generation single-bus symmetric multi-CPU router; the fourth generation multi-bus multi-CPU Structure router, the fifth generation shared memory structure router, the sixth generation cross-Switch Architecture Router Based on the cluster system router and so on. 2) the router consists of four elements: the input port, the output port, the switch and the route processor. The entire router structure is divided into two parts: the route selection part (the core is the route selection processor), the packet forwarding part (input, output, and exchange) route table: only the ing from the target network to the next hop is always implemented by the software. Forwarding Table: obtained from the route table. Each line of the forwarding table must contain the destination network to the output port and some MAC address information. Input Structure: Physical Layer-> link layer-> cached at the network layer, so that IP data cannot be forwarded temporarily in the cache area. Output structure: cached at the network layer-> link layer-> physical layer. 6. Differences between low-end and high-end routes, such as Cisco and TP-LINK routers. 1) the operating frequency and memory capacity of the processor determine the performance of a vro to a large extent. 2) The processor clock speed is only a performance indicator of the processor. Its bus width (16-bit or 32-bit), Cache capacity and structure, internal bus structure, single CPU, multi-CPU distributed processing, computing mode, and other indicators will affect the performance of the processor. Almost all routers use a communications-related CPU. Therefore, "using a communications-related CPU" is equivalent to saying nothing. The key lies in what kernel is used by the CPU and the internal structure. The same is true for the memory. The size of the memory does not matter. If the load is not large, there may not be much difference between the 4 M memory and the 8 M memory, therefore, it is not scientific to judge vro performance based on the memory size (of course, the large memory capacity is still advantageous ). 3) metrics that determine the route level: load capacity, also known as the number of hosts on the belt. For example, everyone in the internet cafe is immersed in online chat and games, and almost all data is through the WAN port of the router, so the load is very heavy; but if it is a corporate network, most people are busy designing, writing reports, and making plans. At the same time, only a small number of people are using the network, and most of the data is flowing inside the enterprise network, so the router load is very light, then, clients with more loads can be simultaneously deployed. 4) outbound traffic refers to the amount of data that can be processed by the router per second. This parameter refers to the throughput of the LAN-to-WAN. The measurement result is that when NAT is enabled and the firewall is disabled, use the Smartbits and Chariot test methods respectively. Summary: 1. vrouters with different performance have powerful built-in processor and large memory capacity, so the cost is relatively high. 2. different applications, vrouters with strong performance can be used for networks with more loads, while low-end vrouters cannot. 3. different functions. Although the basic functions are the same, some routers also have other practical functions, such as professional firewall functions and VPN functions. Therefore, they have high technical requirements, the price will naturally increase. 7. Differences between vrouters and vswitches 1. Loop: An algorithm is established based on vswitch address learning and station table. No loop is allowed between vswitches. Once a loop exists, the Spanning Tree Algorithm must be enabled to block the ports that generate the loop. The router routing protocol does not solve this problem. There are multiple channels between routers to balance the load and improve reliability. 2. Load aggregation: only one channel is available between switches, so that information is concentrated on one communication link and cannot be dynamically allocated to balance the load. The router routing protocol algorithm can avoid this. The OSPF routing protocol algorithm can not only generate multiple routes, but also select different optimal routes for different network applications. 3. Broadcast control: A vswitch can only narrow down the conflicted domain, but not the broadcast domain. The entire exchange network is a large broadcast domain, where broadcast packets are scattered across the entire exchange network. Vrouters can isolate broadcast domains, and broadcast packets cannot be broadcast through vrouters. 4. subnet division: The switch can only recognize MAC addresses. The MAC address is a physical address and uses a flat address structure. Therefore, you cannot divide subnets Based on the MAC address. Vro identifies IP addresses. IP addresses are allocated by network administrators. They are logical addresses and IP addresses have hierarchies. They are divided into network numbers and host numbers, which can be easily used to divide subnets, the main function of a vro is to connect to different networks. 5. confidentiality: although the switch can also filter Frames Based on the source MAC address, target MAC address, and other frames, however, the vro filters packets based on the source IP address, destination IP address, and TCP port address of the packets, making them more intuitive and convenient. 6. media-related: A switch can also be used as a bridge device to convert between the link layer and the physical layer. However, this conversion process is complicated and is not suitable for ASIC implementation. This will inevitably reduce the forwarding speed of the switch. Therefore, currently, vswitches primarily Interconnect Networks with the same or similar physical media and link protocols, instead of connecting networks with different physical media and link layer protocols. Different routers are used for interconnection between different networks, so they can connect networks with different physical media, link layer protocols, and network layer protocols. Although a vro has a functional advantage, it is expensive and has a low packet forwarding speed.