Hello!
This week, I will spend a number of entries to study the protocol SNMP, Simple Netowork Management Protocol - Protocol Simple Network Management, based on the great article
of Debby Koren, "Dean" RAD University .
A historical review Before the advent of SNMP, if you wanted to manage a set of network devices, you should have stations dedicated to management, perhaps with multiple windows for different types of information (statistics, activity, etc.) that were specific to each manufacturer. In fact, it was rare that a manufacturer had a common management station for all your devices.
There was a common protocol, but a lot of proprietary protocols. SNMP was developed to address this problem by offering a protocol for standardized network management so that they could use a common technology for exchanging information consistent between different devices on the network, even those from different manufacturers.
Since the publication of the first RFC SNMP
over 20 years, SNMP has been updated several times and has become a standard which is implemented in almost all network devices. Although it was designed with elements of the Internet, you can find all kinds of devices that support it, as air conditioning. You can also use SNMP to manage software systems. SNMP can be used to monitor, configure and obtain information from devices or programs using graphical interfaces in expensive management teams or using a free management software or even from the CLI.
Components and Architecture
There are 4 basic components of SNMP:
- managed nodes or network elements, which have an agent (agent).
- At least one station network management (NMS)
-
Management Information - A management protocol of the network, using the NMS and the agents to exchange management information
A managed node
can be any system, including a software system that has some kind of network connectivity. In fact, early in the development of SNMP, with the aim of demonstrating the versatility of the protocol, the company showed
Epilogue how you could use SNMP to manage a toaster.
The agent that contains each node implements the protocol management SNMP. The agent is able to send, receive and parse SNMP messages. The agent interacts with the physical device and obtain the information needed to answer the queries of the NMS and to send trap messages (notification messages). The agent is also able to make changes to the configuration of the device following the instructions from the NMS requests. Agents therefore have to have an access control settings to manage the read / write privileges.
A station network management (NMS
) is a host that is capable of sending and receiving SNMP requests and parse responses and SNMP trap messages to / from the managed nodes. NMS There are many commercial software offers many features like the ability to "discover" the management of the network nodes, graphically displaying the nodes in a network map, using icons for each node type, display status information, statistics, etc.
The third component is the SNMP management information, which is obviously the information exchanged between agents and the NMS. We use the term managed object
to refer to a management information unit. Ojo! Do not confuse a managed object to a managed device is not the same. A managed object is an abstract concept, is the definition of a information. For example, suppose you have a device that can change color, we could define a managed object called "color" and its corresponding definition would be "the color of the device."
A collection of related managed objects, which are defined in a document called
MIB module (Management Information Base). We will see that there are some standard MIB modules, which are called simply MIBs, all devices must support SNMP. There are other standard MIB modules should be supported only by devices for which the MIB is relevant, and other private MIB specific to a particular manufacturer, containing definitions of managed objects for their teams.
For example, all SNMP manageable devices must have certain information such as IP address, to be considered compliant with the SNMP protocol, this information should be defined in a standard MIB that all devices must support . If the device has an Ethernet interface, then you should be able to provide certain information such as the number of collisions, and this information is defined in a MIB Ethernet, all devices with an Ethernet interface must support. Finally, a manufacturer of switches, for example, could offer a feature that makes their devices more attractive to customers: the switch can change color to blend into the closet. The manufacturer has to offer, therefore, a private MIB that contain a managed object for this purpose.
Therefore, MIBs contain objects representing managed resources, configuration, status, etc. of a system. Managed objects are assigned values \u200b\u200bto represent them, but not the value itself. For example, following the example of the managed object "color", its definition is "the color of the device" and its assigned value could be 0 for black, 1 for pink, 2 to gray, 3 for green, etc.. In this case, the object would be an integer, and value represent the entire color. Would be precisely the value of managed object which would be monitored and modified by NMS.
And this brings us to the last component of the management architecture: the management protocol of the network. But wait a moment, is not this what we call 'SNMP'? Is not the protocol SNMP network management? SNMP is that and more, as it defines the MIBs, architecture and protocol for exchanging messages. In this latter respect, the message exchange protocol between the NMS and the managed nodes, including the type of messages and formats is the protocol called network management.
We will see in the next outset that there are several types of SNMP messages, which allow the NMS to read and / or write information, and allow agents to send trap messages to notify or alarm of a certain situation.
Management Architecture
SNMP uses a client-server architecture as shown in the figure below:
As the pioneer NMS SNMP requests, while agents in different managed devices (router, switch, server and toaster) passively await these consultations, we can say that the NMS is the client and server agents. Agents listen requests on port UDP 161.
however, also contains the SNMP management protocol traps. As already mentioned, traps are unsolicited messages that are sent to the NMS by the agents to report unusual events or alarms on a given situation. As the agent is the one who initiates the connection, in this case the agents are clients and NMS servers, listening on UDP port 162.
In the next posts we will continue talking about SNMP, MIBs
deepening the , the messages
management and security of the protocol.
Greetings!
