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With the rapid development of Internet, people are no longer satisfied to share information only on the local network , but want to maximize the use of the various regions of the world , all types of network resources, network routing technology has become a key part of the router also will become the most important network equipment. Under the present circumstances, any one of a certain scale computer networks ( such as enterprise networks, campus networks , intelligent building , etc. ) , regardless of the network technology is fast with big , FDDI technology, or ATM technology , are inseparable from the router , otherwise it does not work properly and management.
Router works. Devices in the network (TCP / IP is the IP address of the network ) communicate with each other using their network address. An IP address is the hardware address unrelated "logical" address. Routers only forward packets based on IP addresses . IP address of the structure has two parts, one to define the network number , host number to another part of the definition of the network. Currently , the use of the Internet subnet mask to determine the IP address of the network and host addresses . IP address and subnet mask as also 32bit, and both one to one and provides the subnet mask in the number " 1 " corresponding to the IP address of the part of the network number , "0" by compared with the corresponding host number . The network number and host number together , will constitute a complete IP address. The same network host IP address, network number must be the same , the network is called IP subnet. Communication only between IP addresses have the same network number will be , with a host of other IP subnets to communicate , you must go through a router or gateway (gateway) to go out on the same network . Different IP addresses can not communicate directly with the network number , even if they are connected together and can not communicate. Router has multiple ports for connecting multiple IP subnets. Network number required for each IP address and port number of IP subnets connected to the same network . Different ports for different network numbers , corresponding to different IP subnets , so as to enable the subnet host through its own subnet IP address of the IP packet sent out requests on the router.
The main function of the router . Routing actions include two basic elements: routing and forwarding. I.e., to determine the best routing paths to reach the destination , by the routing algorithm. In order to determine the best path routing algorithm must start and maintain routing table contains routing information , which depends on the routing information used in routing algorithm and different. Routing algorithm will be collected to fill in different information in the routing table , the routing table with the next stop may be the destination network (nexthop) relationship tells the router . Routers exchange routing information updates, update and maintain routing tables make it accurately reflect the changes in the network topology , according to measurements by the router to determine the best path. That is good forwards along the best path routing information packets transmitted . Router first looks in the routing table , to know how to judge whether a packet is sent to the next station ( router or host ) , if the router does not know how to send a packet , the packet is usually discarded ; otherwise it will be grouped according to the corresponding routing table entries sent to the next site , if the purpose of the network is directly connected to the router, put the packet directly to the corresponding port. This is the route forwarding protocol (routed protocol). Forwarding routing protocols and routing protocols is mutual cooperation and mutually independent concepts , the former uses the latter to maintain routing tables , to take advantage of the former while the latter provides functionality to publish routing protocol packets.
Routing protocols . Typical routing in two ways: static and dynamic routing . Static routing is fixed routing table settings in the router. Unless the network administrator intervention , otherwise static route will not change. Static routing can not be made to reflect changes in the network, generally used for small -scale network , fixed network topology . Advantages of static routing is simple, efficient, and reliable. In all routing , static routing highest priority . When the dynamic routing and static routing conflict, static routing prevail. Dynamic routing is the communication between routers in the network , routing information , use a router table update routing information received in the course . It can adapt to changes in real-time network structure . If the routing update information indicates that a network change has occurred , the routing software recalculates the route and issue a new routing updates. Information through various networks , causing the router to restart its routing algorithm, and update their routing tables to reflect the network topology changes dynamically . Dynamic routing for network scale, complex network topology . Of course , a variety of dynamic routing protocols will be different degrees of network bandwidth and CPU resources. Static and dynamic routing have their own characteristics and scope , so dynamic routing in the network as a supplement is usually static routing . When a packet router for routing , static routing router first looks , if found then forwards the packet according to the corresponding static routing ; otherwise find another dynamic routing .
Routing algorithm. Routing algorithms can be classified according to the type of the following categories: static and dynamic , single and multi-channel , equality and grading between source routing and transparent routing , domain and domain , link state and distance vector . Link state algorithm ( also called shortest path algorithm ) to send routing information to all nodes on the Internet , however, for each router , it only sends a routing table that describes a part of its own link state . Distance vector algorithm ( also known as Bellman-Ford algorithm ) is required for each router to send all or part of its routing table information, but only sent to the adjacent node . In essence , link-state algorithms to send a small amount of updates throughout the network, and a lot of distance vector algorithms send updates to neighboring routers . Since the link state algorithm converges faster than distance vector algorithm so it somewhat more difficult in a routing loop. But on the other hand , link-state algorithms require more CPU power and more memory space than distance vector algorithms, thus link-state algorithms will appear in the realization of more expensive . In addition to these differences , the two algorithms can run well in most environments.
Router security maintenance . Routers use loopholes to attack events occur frequently . http://www.ukassignment.org/essayfw/Routers attack would be a waste of CPU cycles , misleading information flow , so that network anomalies and even paralyzed. Hence the need to take appropriate security measures to protect the security of the router. ① Avoid passwords leaked crisis. According to Carnegie Mellon University 's CERT / CC ( Computer Emergency Response Team / Control Center ) , said 80 percent of security breach incident was caused by a weak password . Hackers often use weak passwords or default password attack. Longer passwords , use 30-60 days of password expiration and other measures to help prevent such vulnerabilities. ② Close IP direct broadcast . Smurf attack is a denial of service attack. In this attack , the attacker uses a fake source address to your network broadcast address to send an "ICMP echo" request. This requires that all hosts to respond to the broadcast request . This situation will degrade network performance. Use no ip source-route closed IP directed broadcast address. ③ disable unnecessary services. Emphasis on security routers have to disable some unnecessary local services, such as SNMP and DHCP users rarely use these services , you can disable only when it is absolutely necessary to use . Also, if possible, turn off the router 's HTTP settings, because identity is equivalent to using the HTTP protocol to send an unencrypted password to the entire network. However , HTTP protocol is used to verify that none of the provisions of a one-time password or a valid password . ④ logical access restrictions . The main means of reasonable restrictions on disposal of logical access control list access , restrict remote terminal session to help prevent hackers to gain access to the system logic . SSH is a logical priority access method , but if unavoidable Telnet, may wish to use the terminal access control to restrict access to only trusted hosts . Therefore, users need to Telnet virtual terminal port on the router to use an access list to add . ⑤ block ICMP ping requests. Control Message Protocol (ICMP) to help troubleshoot problems , identify the host being used , such as the attacker provides a device for browsing the web , determine the local time stamp and network mask, and a modified version of the OS information to speculate . Therefore, by eliminating the ability to ping the remote user receives the response request , we can more easily avoid those activities or unattended scanning defense for those looking for easy targets of " script kiddies " (script kiddies). ⑥ Close IP source routing . IP protocol allows a host to specify the data packet routing through your network , rather than allow network components to determine the best path. Legitimate application of this feature is to diagnose connection problems . However, little has been applied for this purpose , in fact , it is the most common use is for reconnaissance purposes network mirroring , or for an attacker to find a backdoor in a private network. Unless you specify this function can only be used to diagnose the fault , or should turn off this feature. ⑦ monitor configuration changes. After users make changes to the configuration of the router , it needs to be monitored. If you use SNMP, so be sure to choose a powerful community strings , it is best to use message encryption provides SNMP. If you do not configure the device remotely managed via SNMP , SNMP device configuration user is best to read-only . Deny write access to these devices , users will be able to prevent hackers altered or closed interfaces. In addition, users need the system log messages sent from the router to the specified server.#p#分页标题#e#
In short, the router plays a pivotal role in the network , it works at the network layer , the network can determine the destination address of each packet and sent the packet on the shortest path to the destination , and the router can also filter data package.
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