Simple Network Management Protocol (SNMP) enables the monitoring of network devices from a central location. The SNMP agent exchanges network management information with SNMP manager software running on a network management system (NMS), or host. The agent responds to requests for information and actions from the manager. The agent also controls access to the agent's management information base (MIB), the collection of objects that can be viewed or changed by the SNMP manager. The SNMP manager collects information on network connectivity, activity, and events by polling managed devices. Communication between the agent and the manager occurs in one of the following forms:
Management Information BaseA management information base, or MIB, is a hierarchy of information used to define managed objects in a network device. The MIB structure is based on a tree structure, which defines a grouping of objects into related sets. Each object in the MIB is associated with an object identifier (OID), which names the object. The "leaf" in the tree structure is the actual managed object instance, which represents a resource, event, or activity that occurs in your network device. MIBs are either standard or enterprise-specific. Standard MIBs are created by the IETF and documented in various RFCs. Depending on the vendor, many standard MIBs are delivered with the NMS software. You can also download the standard MIBs from the IETF Web site, http://www.ietf.org, and compile them into your NMS if necessary.
Enterprise MIBs are developed and supported by a specific equipment manufacturer. If your network contains devices that have enterprise MIBs, you must obtain them from the manufacturer and compile them into your network management software. Table 5.10 lists the enterprise MIBs supported in JUNOS 5.4. Table 5.10. JUNOS Enterprise MIBs
SNMP Traps
Traps report significant events occurring on a network device, most often errors or failures. SNMP traps are defined in either standard or enterprise MIBs. Standard traps are created by the IETF and documented in various RFCs. The standard traps are compiled into the network management software. Enterprise traps are developed and supported by a specific equipment manufacturer. If your network contains devices that have enterprise traps, you must obtain them from the manufacturer and compile them into your network management software. Table 5.11 and Table 5.12 summarize the SNMP traps supported by the JUNOS software. For SNMP version 1, the JUNOS software supports the traps listed in Table 5.11 and Table 5.12. If you need SNMP version 1 traps for BGP and OSPF, you must translate into SMI version 1 format the BGP and OSPF SMI version 2 trap definitions from RFC 1657 ( Definitions of Managed Objects for the Fourth Version of the Border Gateway Protocol [BGP-4] using SMIv2 ) and RFC 1850 ( OSPF Version 2 Management Information Base ). If you need SNMP version 2 traps for BGP and OSPF, you do not need to reformat the SMI version 2 trap definitions in RFCs 1657 and 1850; you use the definitions as they are documented in the RFCs. Table 5.11. Supported SNMP Version 1 Standard Traps
Table 5.12. Supported SNMP Version 1 Enterprise Traps
JUNOS SNMP Agent FeaturesThe JUNOS SNMP agent software consists of an SNMP master agent that delegates all SNMP requests to subagents. Each subagent is responsible for the support of a specific set of MIBs. The JUNOS software supports SNMP version 1 and version 2c. SNMP version 1 is the initial implementation of SNMP that defines architecture and framework for SNMP. SNMP version 2c is the revised protocol, with improvements to performance and manager-to-manager communications. Specifically, SNMP version 2c implements community strings, which act as passwords when determining who, what, and how the SNMP clients can access the data in SNMP agent. The community string is contained in SNMP Get , GetBulk , GetNext , and Set requests. The agent might require a different community string for Get , GetBulk , and GetNext (read-only access) than for Set (read-write access). The JUNOS SNMP implementation supports Set requests only with the ping MIB. To use Set requests with the ping MIB, you must create a MIB view that includes the ping MIB subtree and include the view statement at the [edit snmp community] hierarchy level. The JUNOS implementation of SNMP supports the IPv6 objects defined in RFC 2465, with the exception of ipv6IfStatsTable . The Juniper IPv6 MIB supports additional IPv6 and ICMPv6 statistics. The JUNOS SNMP agent software accepts IPv4 and IPv6 addresses for transport over IPv4 and IPv6. System Logging for SNMP Traps
When a trap condition occurs, whether the SNMP agent sends a trap to an NMS or not, the trap is logged if the system logging is configured to log an event with that syslog severity level. Table 5.13 lists the syslog severity levels for the SNMP traps supported by the JUNOS software. These levels cannot be changed. Table 5.13. System Logging Severity Levels for SNMP Traps
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