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CCNP Practice Question: Consider this SNMP configuration on a Cisco…
Consider this SNMP configuration on a Cisco IOS-XE switch:
snmp-server community public RO snmp-server community private RW snmp-server ifindex persist
What is the purpose of the 'snmp-server ifindex persist' command?
⚠ Common exam trap
A common mix-up: candidates confuse 'persist' with enabling traps or saving community strings, when in fact it specifically stabilizes interface index numbering across reboots.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It prevents SNMP interface indices from changing after a router reload or interface configuration change.
The 'snmp-server ifindex persist' command ensures that SNMP interface indices (ifIndex values) remain consistent across router reloads or configuration changes. This is critical for network management systems (NMS) that rely on stable ifIndex values to correlate interface statistics over time, as without persistence, ifIndex values may be reassigned dynamically upon reboot or interface configuration modifications.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It prevents SNMP interface indices from changing after a router reload or interface configuration change.
Why this is correct
This command enables the persistence of ifIndex values across router reloads and interface reconfigurations. Without it, Cisco IOS assigns interface indices dynamically based on the order in which hardware and subinterfaces are discovered at boot time, so a reload or adding/removing interfaces can shift the indices. By writing the current ifIndex mapping to persistent storage, the command ensures the NMS continues to associate interface statistics with the correct interface.
- ✗
It enables SNMP traps for interface status changes.
Why it's wrong here
SNMP traps for interface status changes are linkUp and linkDown notifications, which are enabled globally with 'snmp-server enable traps' and further refined by 'snmp-server enable traps snmp linkdown' or platform-specific options. They are also sent only after a trap destination is defined with 'snmp-server host'. The 'snmp-server ifindex persist' command only affects the stability of the numeric interface index; it has no relationship to trap generation or notification filtering.
- ✗
It forces SNMP to use persistent storage for community strings.
Why it's wrong here
This command does not move SNMP community strings to persistent storage; community strings are always stored in the running configuration and can be saved to startup-config in non-encrypted form unless 'snmp-server community' uses a hashed form. The persistent storage referenced here is specifically the ifIndex table, which is written to NVRAM or a file to retain interface index bindings. Confusing persistence of ifIndex values with persistence of credentials is a common error, but the command's scope is limited to index stability.
- ✗
It allows SNMP to index interfaces by their names instead of numbers.
Why it's wrong here
SNMP's ifIndex is defined by the IF-MIB as a unique integer assigned to each interface, and this command does not alter that fundamental index type—it only keeps those integers from changing. Name-based identification is handled by a separate OID, ifName (or ifDescr), which already allows NMS platforms to map names to indices regardless of the command's presence. The command neither enables nor disables name-based addressing; it just locks the numeric indices to specific interfaces.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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