Why there is mismatch while discovering a router Between NPM and Router itself?

RB_NMS

As you see below there is mismatch while discovering a router Between NPM and Router itself

Interfaces shown in the router:

Interfaces discovered  by NPM through SNMPv3

The IOS version of the router  is Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M)

GoldTipu

I am sure the below posts will make you understand how we collect the Interfaces from the device and how they been listed under the List Resources.

Tunnel Interface not "discovered" by NPM

No Interface Bandwidth Utilization Data available (Data is not available)

What object IDs (OIDs) does Orion NPM poll for interface information? What types of interface information does Orion NPM poll?

By default, Orion NPM polls the following interface-related OIDs, as listed by type.

Information Type	OID Name	OID Value
Bandwidth - 32-bit Counter	ifInOctets	1.3.6.1.2.1.2.2.1.10
Bandwidth - 32-bit Counter	ifInUcastPkts	1.3.6.1.2.1.2.2.1.11
Bandwidth - 32-bit Counter	ifInNUcastPkts	1.3.6.1.2.1.2.2.1.12
Bandwidth - 32-bit Counter	ifOutOctets	1.3.6.1.2.1.2.2.1.16
Bandwidth - 32-bit Counter	ifOutUcastPkts	1.3.6.1.2.1.2.2.1.17
Bandwidth - 32-bit Counter	ifOutNUcastPkts	1.3.6.1.2.1.2.2.1.18
Bandwidth - 64-bit Counter	ifHCInOctets	1.3.6.1.2.1.31.1.1.1.6
Bandwidth - 64-bit Counter	ifHCInUcastPkts	1.3.6.1.2.1.31.1.1.1.7
Bandwidth - 64-bit Counter	ifHCInMulticastPkts	1.3.6.1.2.1.31.1.1.1.8
Bandwidth - 64-bit Counter	ifHCOutOctets	1.3.6.1.2.1.31.1.1.1.10
Bandwidth - 64-bit Counter	ifHCOutUcastPkts	1.3.6.1.2.1.31.1.1.1.11
Bandwidth - 64-bit Counter	ifHCOutMulticastPkts	1.3.6.1.2.1.31.1.1.1.12
Errors and Discards	ifInDiscards	1.3.6.1.2.1.2.2.1.13
Errors and Discards	ifInErrors	1.3.6.1.2.1.2.2.1.14
Errors and Discards	ifOutDiscards	1.3.6.1.2.1.2.2.1.19
Errors and Discards	ifOutErrors	1.3.6.1.2.1.2.2.1.20
Interface - General	ifName	1.3.6.1.2.1.31.1.1.1.1
Interface - General	ifAlias	1.3.6.1.2.1.31.1.1.1.18
Signal-to-Noise Ratio and Codeword Errors (CMTS only)	docsIfSigQUnerroreds	1.3.6.1.2.1.10.127.1.1.4.1.2
Signal-to-Noise Ratio and Codeword Errors (CMTS only)	docsIfSigQCorrecteds	1.3.6.1.2.1.10.127.1.1.4.1.3
Signal-to-Noise Ratio and Codeword Errors (CMTS only)	docsIfSigQUncorrectables	1.3.6.1.2.1.10.127.1.1.4.1.4
Signal-to-Noise Ratio and Codeword Errors (CMTS only)	docsIfSigQSignalNoise	1.3.6.1.2.1.10.127.1.1.4.1.5

Let me know if you have any further questions.