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Abstract

With the fast development of computer technology and communication technology, computer network occupies a pivotal position in the society, economy and people's lives. Due to the gradual expansion of the computer network, the network user is increasing, the sharp increase in network equipment, more and more complex structure, the function is growing stronger and stronger, at the same time brought great difficulty to the network management. Since the expansion of the network scale and complexity increases, the network management technology has become an increasingly important issue. Network management is to adjust the network status, in order to ensure that it is normal, efficient operation as long as possible, so that network resources can be fully utilized when the network fails to make timely reports and processing, and to coordinate and maintain the normal operation of the network, to improve efficiency and reduce costs. The network topology discovery as an important part of network management, which increasingly shows the importance of heterogeneous, diverse and changing network. For some small network, the network administrator can manually draw the topology map. But for the campus network or medium-sized network, including network equipment and more and connected complex relationship, network structure often change. Still rely on administrators use manual methods for network topology is not realistic, and less efficient, there is an urgent need to be able to automatically generate the network topology diagram to reflect changes in the network topology and dynamic method and platform. The network topology discovery algorithm is proposed to solve this problem. Network protocol or network tools, based topology discovery algorithm, automatically detect network, resulting in the entire network equipment and interconnected relationships and related information. View on the current market, there have been a lot of management software to automatically discover network topology, such as HP's OpenView, IBM's Tivoli and SUN Sun NetManager etc.. These software based commercial purpose of, the price is very expensive and is also high on the hardware environment requirements, the operation is relatively complex. This article is relying on to the campus network research network topology discovery algorithm, which provides the prerequisite and basis for network structure discovery and troubleshooting. This paper analyzes the purpose and tasks of network management, SNMP functionality, architecture, protocol framework, and MIB library; research and analysis of the topology discovery algorithm based on SNMP, ICMP, RIP, OSPF, ARP. SNMP-based topology discovery algorithm: the network topology through access to information in the MIB. This method is found that the high efficiency, the system and network overhead is small, and easy to implement. The downside is that there is no way to find the network does not support the SNMP protocol or not to install the SNMP agent network; Since the router interface an IP routing table is based on a unique IP address as recorded factors, so there is a multi-entry router not directly reflect the network topology. For security reasons, access to the MIB library usually require privileged, if you do not know the router community information, and will not be able to obtain the necessary information. This method is mainly used for single-domain topology discovery, found that the network routing equipment, reflects the overall topology of the network. ICMP-based topology discovery algorithm: This method is based on the simple theory, more reliable, and almost all TCP / IP-based network equipment to support this agreement, so strong adaptability. And performing topology discovery at the same time to detect the activity of the network devices. Inadequacies: ping command can only test the destination IP is reachable, but can not be determined through the middle which routers. With tracert command, you know the way through which the router, but would like to know the connection between the router is hard. During the ping and tracert operation is both time consuming and increase the burden on the network. Some firewall settings ban ICMP packets through the equipment hidden behind a firewall can not detect. RIP-based topology discovery algorithm: the related routing table information can be obtained through the RIP protocol to interact with the router, and from the analysis of the extracted network topology. The advantage of this algorithm is fast, high performance, and found that the structure is more accurate. But the agreement of the various command primitives difficult resolution protocol data units, and the requirements to be tested within the network router had to enable RIP protocol. In addition, because of RIP hop count as a metric, the maximum is 15 jump, which determines that it can only apply to a small network, that search range is smaller, and the RIP is gradually replaced by OSPF, so this algorithm the practicality also become smaller and smaller. Based on OSPF topology discovery algorithm: This method is simply a router to access the area, unlike SNMP-based algorithm that need access to the entire network router. Because OSPF-enabled router link state database is able to reflect the structure of the entire network. Obviously the efficiency and speed of this method has greatly improved, and the use of OSPF LSA update dynamically detect changes in network topology without the need to re-detect. Inadequacies: require all devices support OSPF protocol, OSPF port topology connection information, and OSPF algorithm is very complex, system overhead, difficult to achieve. ARP-based topology discovery algorithm: the ARP table, the network devices are the recent activities of the valid device IP address, and no redundant information, so the discovery of this method is very efficient. But the downside is only suitable for LAN topology, can not be found that the ARP device does not support, ARP table when the network is too large, the records may not include all devices in the network. Generally, the method in combination with other methods, to compensate for the shortage. In this paper, the above algorithm, summed up their advantages and disadvantages, and hierarchical network topology based on SNMP and ICMP protocol discovery algorithm based on the above theory. First discovered devices in the network and the connection between the relationship, through a combination of the the MIB library ipForwarding sysServices value to determine the type of network equipment; corresponding router interface address by the traversal ipAddrTable ipAdEntAddr variable, and select the most The IP address of the router as the identification, so as to achieve the purpose of the incorporation of the multi-IP address for the router. During subnet host is found, the method used in this paper is based on the IP address and mask sub Nets column, and computing, can be available within the subnet host address range. Note To remove the network address of the host bits 0 and host bits all 1s broadcast address, because these two addresses can not be assigned to the host. Make sure that the available range of host IP, ICMP ping command to turn ping packets sent to these IP addresses to confirm the state of the subnet host survival subnet. Subnet host discovery speed asynchronously host discovery that two threads ICMP packet transceiver, thereby reducing the delay of discovery, discovery efficiency. Followed by the implementation of this algorithm, the test results show that the algorithm to achieve the desired objectives. Tested the algorithm is only suited to support the SNMP protocol network topology discovery, NA For those who do not support SNMP network, thus limiting this method; environment based on the actual application, the algorithm does not propose how to find three switches and VLAN; installed on the host firewall settings prohibit ICMP packets, the algorithm will not be able to find this host. Due to the limited time and energy, the algorithm above enough to need further improvement.

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Research of Network Topology Discovery Algorithm

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