For SNMP discovery, the drivers use SNMP to query certain MIB objects on Cisco, Huawei, and Juniper M/T devices for MPLS, VPN, and relationship information. The drivers also query certain MIB objects on Cisco and Juniper M/T devices for BGP and relationship information. One SNMP discovery probe instance is started for each device. Appendix A, “MIBs Accessed for Discovery and Remote Ping,” provides a description of the discovery MIB objects that are polled by an SNMP discovery probe.
The MPLS Topology Server uses a synchronous, multithreaded SNMP discovery probe. SNMP discovery may run in as many as 10 concurrent threads.
The SNMPVersion attribute of a device’s SNMPAgent determines whether a probe sends an SNMPv1, v2, or v3 request to the device.
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If SNMPVersion is V1, the SNMP discovery probe creates and sends an SNMPv1 request that includes the SNMP credential that is specified in the SNMPAgent’s ReadCommunity attribute.
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If SNMPVersion is V2C, the SNMP discovery probe creates and sends an SNMPv2 request that includes the SNMP credential that is specified in the SNMPAgent’s ReadCommunity attribute.
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If SNMPVersion is V3, the SNMP discovery probe creates and sends an SNMPv3 request that includes the SNMP credentials that are specified in the SNMPAgent’s User, AuthPass, AuthProtocol, PrivPass, PrivProtocol, and EngineID attributes.
For an AuthPass or PrivPass attribute value, the probe uses the “site key” to decrypt a copy of the value just before it creates and sends the SNMPv3 request. As explained in the System Administration Guide , the site key is created during the installation of applications.
If the probing of a device is successful, the MPLS Topology Server creates an object for each discovered MPLS, VPN, or BGP component and places the objects in its repository. If the probing is not successful, the MPLS Topology Server places the name of the probed device on the Pending Elements list. Chapter 9, “Understanding Discovery Results,” provides information about discovery errors and the Pending Elements list.
