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SNMP

3 roadmaps35 questions

Managers poll MIB objects over UDP with Get and GetBulk, agents push traps and informs, and v3 adds per-user auth and encryption. Network gear still speaks it, so monitoring interviews reach it.

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In SNMP's AgentX protocol, what do the master agent and its subagents each do, and why does the manager never see the split?

level: middleimportance: nice to knowfreq 7%

basics

~20 s

An AgentX master agent speaks SNMP on the agent's address and enforces access control and MIB views; subagents register MIB regions with it and hold the actual instrumentation. RFC 2741 makes the split invisible: managers see one ordinary agent.

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A revised vendor MIB module keeps an object's OID but changes its SYNTAX from Counter32 to Gauge32; which SMIv2 rule does that break, and what should the revision have done?

level: seniorimportance: nice to knowfreq 10%

basics

~20 s

It breaks RFC 2578's rule that a registered OID's semantics never change: a SYNTAX change outside the allowed list needs a new OID. The revision should define a new object at an unassigned OID and mark the old one deprecated or obsolete.

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An SNMP SetRequest with three variable bindings returns inconsistentValue with error-index 2; which of the three changes did the agent apply, and why?

level: seniorimportance: nice to knowfreq 10%

basics

~20 s

An SNMP agent assigns nothing: RFC 3416 has it validate every SetRequest binding before assigning any, so a validation error such as inconsistentValue on binding 2 leaves all three unchanged; the manager fixes that binding and resends the request.

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What does a Response to an SNMP InformRequest actually prove, and what can still be lost or duplicated after the agent receives it?

level: seniorimportance: nice to knowfreq 10%

basics

~20 s

A noError Response to an InformRequest proves the receiving SNMP entity accepted the notification and passed it to its receiver application. It does not prove storage, alerting or a human, and a lost Response makes the agent resend a duplicate.

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Using SNMPv3's VACM, how would you give a NOC group read-write access and an automation account read-only access to interface objects only?

level: seniorimportance: nice to knowfreq 10%

basics

~20 s

Map each USM user to a VACM group, give the group an authPriv access row naming read, write and notify views, and build views from included and excluded OID subtrees. The automation group gets an interfaces-only read view and no write view.

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