SNMP ifindex Persist Global vs Interface

Troubleshoot SNMP (v2c, v3)

Answer Correct answer: D — Configure the snmp ifindex persist command globally to retain ifIndex values across reboots.

An engineer received a ticket about a router that has reloaded. The monitoring system graphs show different traffic patterns between logical and physical interfaces when the router is rebooted. Which action resolves the issue?

Configure the snmp ifindex persist command on the physical interfaces.
Clear the logical interfaces with snmp ifindex clear command.
Trigger a new snmpwalk from the monitoring system to synchronize interface OIDs.
Configure the snmp ifindex persist command globally. Correct Answer

Community Votes

63%

37%

63% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

Tests knowledge of SNMP persistence scope: global configuration ensures consistent ifIndex values across reboots for all interfaces, preventing monitoring graph anomalies.

Resolves SNMP ifIndex mismatch on logical interfaces after router reload by configuring the snmp ifindex persist command globally.

Many users choose A (interface config) because they assume per-interface settings are needed, but the command is not valid in interface configuration mode.

Community Discussion (7 comments)

Brahim90 👍 1 Selected: D

Given answer is correct. Per cisco book page 882. It is supported in the Global config mode.

9410480 👍 4 Selected: A

"snmp ifindex" syntax is not valid in global-config mode, only in if-config.

RickAO76 👍 3 Selected: D

.... " logical and physical interfaces " crap, I'm going back to voting for D now, since placing on each interface would not make much sense.

RickAO76 👍 3 Selected: A

....So just looking at the reference from "d740f62" "snmp-server ifindex persistence" = global command "snmp ifindex persistence" = command from interface D - is trying to use the interface command globally. A - seems right.

Defilet 👍 3 Selected: D

the SNMP ifIndex persistence feature provides an interface index (ifIndex) value that is retained and used when the switch reboots. Should be D

d740f62 👍 4 Selected: D

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SY/configuration/guide/sy_swcg/snmp_if_index_persistence.pdf

Pietjeplukgeluk 👍 1 Selected: C

If OID has changed they should be synchronized i guess. Also the question is not to prevent this issue in near future. I guess C is best here.

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Expert Analysis

Why the Answer Is Correct

The issue stems from SNMP ifIndex values changing after a reboot, causing monitoring systems to map traffic to wrong logical interfaces. The correct solution is to configure snmp ifindex persist in global configuration mode. This feature ensures that ifIndex values are retained and reused upon reboot, maintaining consistency between physical and logical interfaces.

Why the Other Options Are Wrong

Option A is incorrect because the snmp ifindex persist command is not valid in interface configuration mode; it must be applied globally. Option B is wrong as there is no standard snmp ifindex clear command for this purpose, and clearing would exacerbate the issue. Option C is ineffective because triggering a new walk does not fix the underlying index instability; the monitoring system will still see shifting indices.

Community Comment Notes

Community discussion highlights confusion between global and interface modes. One commenter noted, "snmp ifindex syntax is not valid in global-config mode, only in if-config" but later clarified the reference shows it's a global command. Another user confirmed, "Per cisco book page 882. It is supported in the Global config mode." The consensus supports D despite initial doubts about interface-specific application.

Official Reference

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SY/configuration/guide/sy_swcg/snmp_if_index_persistence.pdf

Exam Strategy

Always verify the configuration mode validity for specific commands. For SNMP persistence features that affect system-wide stability like ifIndex, look for global configuration options rather than interface-specific ones.

Frequently Asked Questions

Can snmp ifindex persist be configured per interface?

No, the command is only valid in global configuration mode. Applying it per interface results in a syntax error.

Does clearing SNMP cache fix the issue?

No, clearing cache does not prevent ifIndex changes on reboot. Persistence must be enabled globally to ensure stability.

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