what is the correct snmptrap command format?

Question

Which of the following is the correct format for snmptrap (net-snmp) command?

snmptrap -v 2c -c public host "" NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification \
       netSnmpExampleHeartbeatRate i 123456

or

snmptrap -v 2c -c public host "" NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification \
       netSnmpExampleHeartbeatRate.0 i 123456

i.e., with or without .0 in the variable bindings?

Actually both of these formats work, but which one is right or what is the difference?

Answer 1

It depends if "scalar" or a "table row"-related varbinds are being referred to in the trap.

http://www.net-snmp.org/wiki/index.php/TUT:snmptrap states :

Note that this command also includes an (OID,type,value) triple for the varbinds listed in the VARIABLES clause (in the same way as with the snmpset command).

Table row example.

snmptrap -v 2c -c public host:162 .1.3.6.1.6.3.1.1.5.3 .1.3.6.1.6.3.1.1.5.3    \
        ifIndex i 2 ifAdminStatus i 1 ifOperStatus i 1

For reference :

snmptranslate -m +ALL -Pu .1.3.6.1.6.3.1.1.5.3
IF-MIB::linkDown

No .0 in the variable bindings since id is taken care of by the ifIndex which pinpoints the row.

Scalar row example.

http://www.net-snmp.org/wiki/index.php/TUT:snmptrap shows example

snmptrap -v 1 -c public host UCD-TRAP-TEST-MIB::demotraps "" 6 17 "" \
       SNMPv2-MIB::sysLocation.0 s "Just here"

'SNMPv2-MIB::sysLocation.0' is a scalar.

Unlike IF-MIB::linkDown example above, which was related to a table row id-ed by the ifIndex, here the .0s at the end pinpoints the scalar (like when you SET it)

Netsnmp example from original question

mibs/NET-SNMP-EXAMPLES-MIB.txt states

netSnmpExampleHeartbeatRate OBJECT-TYPE
    SYNTAX      Integer32
    MAX-ACCESS  accessible-for-notify
    STATUS      current
    DESCRIPTION
        "A simple integer object, to act as a payload for the
         netSnmpExampleHeartbeatNotification.  The value has
         no real meaning, but is nominally the interval (in
         seconds) between successive heartbeat notifications."
::= { netSnmpExampleNotificationObjects 1 }

i.e. it is not a real, identifiable, accessible scalar so I recommend no .0.