Nagios Support Forum

This makes it look like 1296 is an invalid interface ID:

IF-MIB::ifOperStatus.1296 = No Such Instance currently exists at this OID

What does this output?
And this:

snmpwalk -v3 -u 'abc' -A 'xyz' -a 'SHA' -l 'authNoPriv' 10.x.x.x ifOperStatus | grep '1296'
IF-MIB::ifOperStatus.1296 = INTEGER: unknown(4)

snmpwalk -v3 -u 'abc' -A 'xyz' -a 'SHA' -l 'authNoPriv' 10.x.x.x ifOperStatus
IF-MIB::ifOperStatus.32 = INTEGER: up(1)
IF-MIB::ifOperStatus.624 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.640 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.656 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.672 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.688 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.752 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.768 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.784 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.800 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.816 = INTEGER: up(1)
IF-MIB::ifOperStatus.832 = INTEGER: up(1)
IF-MIB::ifOperStatus.848 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.864 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.880 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.896 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.912 = INTEGER: up(1)
IF-MIB::ifOperStatus.928 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.944 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.960 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.976 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.992 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.1008 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1024 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1040 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1056 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1072 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.1088 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1104 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1120 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1136 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1152 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.1168 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1184 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1200 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1216 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1232 = INTEGER: notPresent(6)
IF-MIB::ifOperStatus.1248 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1264 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1280 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1296 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1344 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1360 = INTEGER: unknown(4)
IF-MIB::ifOperStatus.1376 = INTEGER: up(1)
IF-MIB::ifOperStatus.1392 = INTEGER: up(1)
IF-MIB::ifOperStatus.1424 = INTEGER: up(1)
IF-MIB::ifOperStatus.1440 = INTEGER: up(1)
IF-MIB::ifOperStatus.1456 = INTEGER: up(1)
IF-MIB::ifOperStatus.1472 = INTEGER: up(1)
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ifOperStatus.1296 is showing as unknown(4), it likely has issues or something on the remote system.

Does this one work?

[root@nagios: /usr/local/nagios/libexec]# ./check_ifoperstatnag 1296 -v3 -u 'xyz' -A 'abcdef' -a 'SHA' -l 'authNoPriv' 10.x.x.x
UNKNOWN - No info is being retrieved

we need to conclude on the root cause I believe

You would need to reach out to f5 and ask them what unknown(4) means, that's why it's not working. I searched and was unable to find what that refers to.

The plugin doesn't understand what to do with unknown(4) so it defaults to UNKNOWN.