Communication model deals with how the management data is communicated between the agent and manager process. It is concerned with the transport protocol, the application protocol, and commands and responses between peers. The Functional model addresses the network management applications that reside upon the network management station (NMS). The OSI network management model categorizes five areas of function, sometimes referred to as the FCAPS model: This network management model has gained broad acceptance by vendors as a useful way of describing the requirements for any network management system.
Content 6.2 Network Management 6.2.3 SNMP and CMIP standards To allow for interoperability of management across many different network platforms, network management standards are required so that vendors can implement and adhere to these standards. Two main standards have emerged: Simple Network Management Protocol (SNMP) actually refers to a set of standards for network management, including a protocol, a database structure specification, and a set of data objects. SNMP was adopted as the standard for TCP/IP internets in 1989 and became very popular. An upgrade, known as SNMP version 2c (SNMPv2c) was adopted in 1993. SNMPv2c provides support for centralized and distributed network management strategies, and included improvements in the structure of management information (SMI), protocol operations, management architecture, and security. This was designed to run on OSI based networks as well as TCP/IP based networks. Since then SNMPv3 has been released. To solve the security shortcomings of SNMPv1 and SNMPv2c, SNMPv3 provides secure access to MIBs by authenticating and encrypting packets over the network. The common management information protocol (CMIP) is an OSI network management protocol that was created and standardized by the ISO for the monitoring and control of heterogeneous networks. Web Links CMIP http://www.cisco.com/en/US/tech/ tk472/tk473/ tk119/tech_protocol_ home.html
Content 6.2 Network Management 6.2.4 SNMP operation Simple Network Management Protocol (SNMP) is an application layer protocol designed to facilitate the exchange of management information between network devices. By using SNMP to access management information data, such as packets per second sent on an interface or number of open TCP connections, network administrators can more easily manage network performance to find and solve network problems. Today, SNMP is the most popular protocol for managing diverse commercial, university, and research internetworks. Standardization activity continues even as vendors develop and release state-of-the-art SNMP-based management applications. SNMP is a simple protocol, yet its feature set is sufficiently powerful to handle the difficult problems involved with the management of heterogeneous networks. The organizational model for SNMP based network management includes four elements: The network management station (NMS) is usually a standalone workstation, but it may be implemented over several systems. It includes a collection of software called the network management application (NMA). The NMA includes a user interface to allow authorized network managers to manage the network. It responds to user commands and issued commands to management agents throughout the network. The management agents are key network platforms and devices, other hosts, routers, bridges and hubs, equipped with SNMP so that they can be managed. They respond to requests for information and requests for actions from the NMS, such as polling, and may provide the NMS with important but unsolicited information, such as traps. All the management information of a particular agent is stored in the management information base on that agent. An agent might keep track of the following: The NMS performs a monitoring function by retrieving the values from the MIB. The NMS can cause an action to take place at an agent. The communication between the manager and the agent is carried out by an application layer network management protocol. SNMP uses User Datagram Protocol (UDP) and communicates over ports 161 and 162. It is based on an exchange of messages. There are three common message types: This model is referred to as a two-tier model. However, it assumes that all network elements are manageable by SNMP. This is not always the case, as some devices have a proprietary management interface. In these cases, a three-tiered model is required. A network manager who wants to obtain information or control this proprietary node communicates with a proxy agent. The proxy agent then translates the manager’s SNMP request into a form appropriate to the target system and uses whatever proprietary management protocol is appropriate to communicate with the target system. Responses from the target to the proxy are translated into SNMP messages and communicated back to the manager. Network management applications often offload some network management functionality to a remote monitor (RMON) probe. The RMON probe gathers management information locally, and then the network manager periodically retrieves a summary of this data. The NMS is an ordinary workstation, running a typical operating system. It has a large amount of RAM, to hold all the management applications running at the same time. The manager runs a typical network protocol stack, such as TCP/IP. The network management applications rely on the host operating system, and on the communication architecture. Examples of network management applications are Ciscoworks2000, HP Openview, and SNMPv2c. As discussed before, the manager may be a standalone, centralized workstation sending out queries to all agents, no matter where they are located. In a distributed network, a decentralized architecture is more appropriate, with local NMS at each site. These distributed NMS can act in a client-server architecture, in which one NMS acts as a master server, and the others are clients. The clients send their data to the master server for centralized storage. An alternative is that all distributed NMSs have equal responsibility, each with their own manager databases, so the management information is distributed over the peer NMSs. Web Links SNMP and MIB Basics http://www.adventnet.com/products/ cagent/help/ Preface/ intro_snmpmib.html
Content 6.2 Network Management 6.2.5 Structure of management information and MIBs A management information base (MIB) is used to store the structured information representing network elements and their attributes. The structure itself is defined in a standard called the structure of management information (SMI), which defines the data types that can be used to store an object, how those objects are named, and how they are encoded for transmission over a network. MIBs are highly structured depositories for information about a device. Many standard MIBs exist, but more MIBs that are proprietary exist to uniquely manage different vendor’s devices. The original SMI MIB was