What Is SNM:
snm stands for simple network management protocol. it is a protocol used by many device manufacturers to monitor devices on the local area network. some of these manufacturers are hp, cisco, 3com etc. snmp is the most successful of these protocols and its main use is in network monitoring systems.
Features of snmp:
1) applications can access snmp information about remote devices that run snmp agents, creating applications that locate and manage remote resources located anywhere on an enterprise intranet or Internet2 .
2) data objects describe resources available from a managed device, including hostnames3 , IP addresses4 , system uptime5 , configuration variables6 , attached peripherals7 , and performance statistics8 .
3) an agent program running on a device manages its resources. snmp network management systems (NMSs) and other applications access the information held by agents through the use of managers, which implement snmp manager functions9 .
4) managers and agents do not need to be on common networks because an NMS can carry out all operations remotely10 ,11 .
5) snmpv1 and snmpv2c both offer security measures, such as authentication12 , message integrity13 , data encryption14 , and public-key certificates15 .
6) interfaces to different transport protocols allow easy integration with other system components16 .
7) applications or scripts can send commands directly to agents or request information from them17 .
8) snmp uses open systems interconnection (OSI) model-based layered protocols that integrate data from many different types of hardware and software components in a network18 .
9) this integration and standardization simplifies the task of managing heterogeneous networks.
10) applications use the object-oriented management information base19 , or MIB20, to specify which parameters they want the agent to monitor and control21 .
11) an agent typically exports all information in its database as objects22,23 . agents can support several different versions26 of the protocol: v1, v2c, and v327 .
12) when managers address objects on agents. they must include specific object identifiers28 , called oids29 .
13) the snmpv1, v2c, and v3 protocols are backward-compatible: a manager that uses one of these versions can communicate with an agent that uses an earlier version30.
14) the snmpv3 protocol offers more security options than earlier versions31.
snmp is a very important tool for managing and monitoring networks. it has been in use for many years and continues to be refined and updated. its main features include the ability to access information about remote devices, support for multiple transport protocols, and the use of open systems interconnection model-based layered protocols. this allows it to integrate data from many different types of hardware and software components in a network, making it simpler to manage heterogeneous networks. applications use the object-oriented management information base to specify which parameters they want agents to monitor and control, and the snmpv1, v2c, and v3 protocols are backward-compatible. this allows managers using earlier versions of the protocol to communicate with agents that use later versions.
snmpset is used for setting up or modifying an entry in snmp agent’s configuration file called snmpd.conf. it is also one of the most commonly used tools for configuring SNMP agents (SNMP enabled devices). this tool uses requests formatted as a subset of structured english sentences (the activate requests)
For setting up snmp:
it is necessary to understand what type of services each version of snmp implements. this is because different devices might support different services (e.g., remote disk, remote login), and certain services may not be available on all versions of snmp.
The activate requests are broken down into the following categories:
1) system information
2) getting/setting values within an agent’s database
3) reading/writing to files stored on the local filesystem
4) writing to arbitrary locations in memory
5) executing programs locally which return results to the snmp application
6) sending unsolicited notifications to other SNMP applications or SNMP managers29 .
the activate requests can be further classified into queries and modifications. the query requests are used to read information from the device, while modification requests update or change that information30 .
The following examples show how these queries/modifications work:
snmpget is one of the most commonly used tools for querying snmp agents (SNMP enabled devices). it uses requests formatted as a subset of structured english sentences32 . some commonly used queries are listed below.
1) getnext retrieves information about the next node in an SNMP manager’s list of objects. this request is often used when traversing a table, since it allows the next item to be retrieved without having to know its oid number33 .
2) get retrieves information from a single object34.
3) get-next retrieves information about the next node in an SNMP manager’s list of objects35 . a version of the above example would be:
the snmpget tool can also be used to query multiple devices at once using wildcards36. this allows queries to be sent without knowing oids or IP addresses, which is especially useful when working with large networks38 .
The following command shows how this request might look, although it does not work on all implementations39 . for example:
snmptable displays all values within one or more tables40 . this is particularly useful if you do not know the name of the table(s) you want to query.
the snmpset tool can be used to modify information in an agent’s database41. it uses requests formatted as a subset of structured english sentences42 . some commonly used modifications are listed below.
1) set sets a new value for an object43.
2) add adds a new value to an object44 .
3) delete deletes a value from an object45 .
4) replace replaces an existing value with a new one46 .