How to find the right OID

[Bit Gossip <bit.gossip@xxxxxxxxx>]

Hi Group,
if i am asked to configure R2 to send an inform when the number of
received echo requests reaches 100.
How can I find the right oid to put in the RMON?

This is as far I can go:
r1#show snmp mib | include icmp     
icmp.1
icmp.2
icmp.3
icmp.4
icmp.5
icmp.6
....

but how can I determine that what I need is icmp.8.0?

rmon alarm 23 icmp.8.0 5 absolute rising-threshold 100 11
falling-threshold 100

Thanks,
Luca.