Router technology Overview

In today's information society, people are increasingly demanding data communication. As the core equipment of the IP network, vro has become a key technology in the information industry.
Vro
A router is a packet forwarding device that works at the network layer of the OSI reference model. The router forwards data packets to achieve network interconnection. Although routers support multiple protocols, such as TCP/IP, IPX, SPX, and AppleTalk, most routers in China run TCP/IP protocols.
A router is usually connected to two or more logical ports identified by IP subnet or Point-to-Point Protocol, and has at least one physical port. The router decides the output port and Next Hop address based on the network layer address in the received data packet and the route table maintained inside the router, and overwrites the data packet header at the link layer to forward the data packet.
A Router usually dynamically maintains a route table to reflect the current network topology. The router maintains the route table by exchanging routing and link information with other routers on the network. Vro is the core device connecting to the IP network.
Vro category
The current vro classification methods vary. Various classification methods are associated, but they are not completely consistent.
In terms of capabilities, routers can be divided into high-end routers and low-end routers. Different manufacturers are divided into different categories. Generally, a router with a backplane switching capability greater than 40 GB is called a high-end router, and a router with a backplane switching capability of less than 40 GB is called a low-end router. 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.
In terms of structure, routers can be divided into modular and non-modular structures. High-end routers are generally modular, and low-end routers are non-modular.
Vrouters can be divided into core routers and access routers according to their network locations. The core router is located in the network center and usually uses a high-end router. Fast Packet switching capability and high-speed network interfaces are required, usually in a modular structure. The Access Router is located at the edge of the network, and usually uses a low-end or middle-end router. Relatively low-speed ports and strong access control capabilities are required.
In terms of functions, routers can be divided into general-purpose routers and dedicated routers. Generally, the router is a general-purpose router. A vro is usually used to optimize router interfaces and hardware for specific functions. For example, the Access Server is used as the access dialing user to enhance the PSTN interface and signaling capabilities. The VPN Router enhances the tunnel processing capability and hardware encryption. The Broadband Access Router emphasizes the number and type of broadband interfaces.
In terms of performance, routers can be divided into line rate routers and non-line rate routers. Generally, a wire speed router is a high-end router that can forward data packets at the Media rate. The low-end router is a non-wire speed router. However, some new broadband access routers also provide fast-forward capabilities.
There are still many router classification methods, and as the development of router technology, there may be more and more classification methods.
Router Functions

Vrouters generally implement the following basic functions:

Implements Internet protocols such as IP, TCP, UDP, and ICMP.
Connect to two or more packet exchange networks. Implement the required functions for each connected network. These functions include:
IP data packets are encapsulated in link layer frames or IP data packets are retrieved from link layer frames.
Sends or receives IP data packets based on the maximum data packet size supported by the network. The maximum transmission unit (MTU ).
Converts the IP address and the link layer address of the corresponding network. For example, convert an IP address to an Ethernet hardware address.
Implement traffic control and Error Indication supported by the network.
Receives and forwards data packets, implements buffer management, congestion control, and fair processing during transmission and receiving.
When an error occurs, identify the error and generate ICMP errors and necessary error messages.
Discards data packets whose TTL domain is 0.
Segment data packets if necessary.
Select the next hop destination for each IP packet according to the route table information.
Supports at least one Internal Gateway Protocol (IGP. Supports external Gateway Protocol Exterior Gateway Protocol and EGP) to exchange topology information with other autonomous domains.
Provides network management and system support mechanisms, including storage/upload configuration, diagnosis, upgrade, status report, exception report, and control.
Router Technology
1. router software
The most important technology in router technology is software technology. Routing software is one of the most complex software. Some routing software runs on UNIX operating systems, some routing software runs on embedded operating systems, and some software itself is an operating system to improve efficiency. Cisco, the world's largest router manufacturer, once claimed to be a software company. It can be seen that the router software plays an important role in router technology.
Vro Software generally provides other functions such as routing protocol, table-based forwarding, and management and maintenance. Due to the large scale of the Internet, the route table running on the internet router is very large, which may contain several 100,000 routes. Look-up table forwarding can be imagined very heavy. In high-end routers, the above functions are generally implemented by ASIC chip hardware.
The high complexity of the routing software, on the other hand, reflects the high reliability, high availability and robustness. The functions of the routing software are not complex. In the free sharing software, we can even obtain the source code for the implementation of the routing protocol and data forwarding. However, the difficulty is that the software runs 24 hours a day on a 24-hour basis every year for 365 days.
During the development of the router, you can quickly implement the router by purchasing the commercial source code. However, it usually takes one or even two years to stabilize the router software.
2. Programmable ASIC
The ASIC chip is a dedicated integrated circuit and is the core technology of the current vro for data forwarding at line rate. Programmable ASIC integrates multiple functions on a single chip. It has the advantages of simple design, high reliability, and low power consumption, so that devices can achieve higher performance and lower costs.
The use of ASIC chips can also increase the port density of devices. The port density of an ASIC chip is several times that of a General chip.
The design of the programmable ASIC chip is the hardware guarantee implemented by the current high-performance router.
3. router interface
A router interface is used to connect a router to a network. It can be divided into two types: LAN interface and WAN interface. LAN interfaces mainly include Ethernet (10 M, M and M Ethernet), card ring, Token Bus, FDDI and other network interfaces. Wan mainly includes E1/T1, E3/T3, DS3, universal serial port can be switched to X.21 DTE/DCE, V.35 DTE/DCE, RS232 DTE/DCE, RS449 DTE/DCE, EIA530 DTE) ATM interface, POS interface, and other network interfaces.
At present, the router interface technology is mature, and the difficulty lies in the design and production of high-density interface boards and the implementation of high-speed interfaces greater than/equal to 2.5 Gbps.
Routing Protocol
The realization of router routing protocol is an important part of router software. The routing protocol is used to establish and maintain a route table. The route table is used to select the output port or next hop address for each IP packet. Open routing protocols include RIP/r00002, OSPF, IS-IS, and BGP4.
RIP/RIPv2, OSPF, and IS-IS are used AS intra-Domain Routing Protocols. They are generally used inside the AS (Autonomous System) to calculate and exchange network accessibility messages within the. RIP/r00002 is a distance vector routing protocol, which is generally used in small-scale networks within an enterprise. The principles and implementations of OSPF and IS-IS are similar. They are link status protocols and are generally used for large-scale enterprise networks or carrier networks.
The BGP4 protocol is based on the distance vector and is the only choice of the routing protocol between. Generally, BGP exchanges a large amount of network accessibility messages, which is an important protocol on the IP network.
The implementation of the routing protocol is similar to that of the router software. Therefore, it must be highly reliable, stable, robust, and secure. Router performance
Vro performance generally includes the following content:
Backplane capability: generally refers to the backplane capacity or bus capability of the router.
Throughput: the forwarding capability of a vro package.
Packet Loss Rate: the proportion of data packets that cannot be forwarded in the data packets to be forwarded due to lack of resources under a stable and sustained load.
Forwarding latency: the time interval when the last bit of the data packet to be forwarded enters the router port to the first bit of the data packet that appears on the Port Link.
Route table capacity: the number of routes that can be accommodated when the vro is running.
Reliability: indicators such as vro availability, no-fault working time, and fault recovery time.
Vro Queue Management Mechanism
Because a router is a group-based switch device and bandwidth statistics are reused on each port, the router must maintain one or more queues on the port, otherwise, the router cannot handle multiple data packets forwarding to the same port at the same time, as well as QoS capabilities on the port. The quality of queue management algorithms directly affects the performance, QoS, and congestion management of routers. Generally, queue management algorithms are classified into time-based algorithms, rotation-based algorithms, and priority-based queues.
The time-based grouping scheduling algorithms share the same format. They maintain two time-scales for each group, and one is named start time-stamp ), name it "finish time-stamp ). The vro determines the next data packet based on the above time points. The most common time-based algorithms are WFQ and WF2Q.
Another type of scheduling algorithms are based on the rotation scheduling mechanism. Their working principle is similar to the multi-task rotation scheduling in the operating system. Rotation-based scheduling algorithms include WRR and DRR.
Priority-Based Queue Management can schedule packet forwarding for different queues based on predefined or user-specified priorities.
Routers usually use RED Early Detection and WRED weighted early detection in the queue to avoid congestion.
MPLS Technology
As an efficient IP backbone network technology platform, MPLS technology provides a flexible and scalable backbone network exchange technology for the next generation of IP networks. Using MPLS technology can greatly improve network operation efficiency, achieve QoS division for IP network services, and rationally allocate network resources through traffic engineering, implement constrained routing. With these capabilities, MPLS networks can also provide efficient VPN services and real-time services. It can be said that MPLS technology is likely to become a key technology in the evolution of an IP network to the next generation of telecom-grade IP networks. Therefore, MPLS technology may also be the key to whether a router is the core device of the next-generation IP network.
Although MPLS has various advantages, it has not been widely used on the Internet. The reason is that the Protocol is not mature, there are problems with multi-vendor interoperability, MPLS cross-AS or even cross-Area problems, VC Merge (VC merger) needs to be studied. However, at present, MPLS is the best solution to achieve network-based VPN and can implement traffic engineering. In the future, the possibility of adopting MPLS must be explored in the study of IP networks. The router device must consider implementing MPLS.
VPN Technology
VPN refers to creating a virtual private network on a public network. VPN can be classified from different angles:
By access method
VPN: a VPN implementation solution provided for users who have connected to the ISP edge router through a leased line.
Dial-up VPN (VPDN): refers to the VPN service provided for users who use dial-up PSTN or ISDN to access ISP.
By protocol type
L2 tunnel protocol: point-to-point tunnel protocol (PPTP), L2 forwarding protocol (L2F), and L2 tunnel protocol (L2TP ).
Layer-3 tunneling protocols: Common routing and encapsulation protocols (GRE) and IP Security (IPSec ).
The MPLS Tunneling Protocol can be seen between Layer 2 and Layer 3.
By VPN initiation:
Customer initiation (also known as customer-based): the starting point and ending point of VPN service provision are oriented to customers, and their internal technical structure, implementation and management are visible to VPN customers.
Server initiation (also known as the customer's transparent or network-based): Install VPN software at the company's Central Department and ISP (known as POP) without the need to install any special software.
Divided by the current carrier type:
Dial-up VPN Service (VPDN): VPDN in the first partitioning method.
Virtual leased line (VLL): It is a simulation of Traditional Leased Line Services and simulates the leased line using an IP network. In the view of users at both ends of such a virtual lease line, this virtual lease line is equivalent to the previous lease line.
VPRN services: There are two types of services. One is the VPRN implemented using traditional VPN protocols, such as IPSec and GRE. The other is mpls vpn.
QoS on the router
QoS on a vro can be obtained through the following methods:
You can obtain it through high bandwidth. In addition to increasing the interface bandwidth on the vro, no extra work is required to ensure QoS.
Since data communication is not guaranteed by a recognized mathematical model, this method can only roughly use empirical values for estimation. It is generally considered that expansion should be performed after the bandwidth utilization reaches 50% to ensure that the interface bandwidth utilization is less than 50%.
Implemented through end-to-end Bandwidth Reservation. This method uses RSVP or similar protocols to reserve end-to-end bandwidth between nodes that communicate across the network. This method can ensure QoS, but the cost is too high. It usually runs only on the enterprise network or private network and cannot be implemented on the large public network.
It can be obtained through access control, congestion control, and service DiffServ differentiation. This method cannot completely guarantee QoS. This can be used in combination with the increase of interface bandwidth to provide a certain degree of CoS.
Obtained Through MPLS Traffic Engineering.
Vro Security
The security of a router is divided into two aspects: the security of the router itself, and the security of data.
Vro is the core of the Internet and a key device for network interconnection. Therefore, the security requirements of routers are higher than those of other devices. A host's security vulnerability causes the host to be inaccessible at most, and a vro's security vulnerability may cause the entire network to be inaccessible.
Vro security vulnerabilities may be caused by management and technical reasons. In terms of management, poor selection of vro passwords, improper use of the routing protocol authorization mechanism, and incorrect routing configurations may cause problems in the router operation. Technical vro security vulnerabilities may include the following:
Malicious attacks. Such as eavesdropping, traffic analysis, counterfeiting, re-transmission, denial of service, unauthorized resource access, interference, viruses, and other attacks.
Software vulnerabilities. Backdoor, operating system vulnerabilities, database vulnerabilities, TCP/IP protocol vulnerabilities, and network services may all have vulnerabilities.
The security of data transmitted by routers can be provided by the network or by users. If provided by the network, it is only related to the access router. Generally, the Access Router can provide an IPSec Security channel to ensure security.