Curious message during activation of snmp traps in cisco router 2800

Question

I activated snmp traps in cisco router 2800 (I didn't specify a set of them, so all of them were activated). The thing is, when i configure "snmp-server enable traps", appears a message in the next line :
" %Cannot enable both sham-link state-change interface traps.
   %New sham link interface trap not enabled "
Anyway, traps are activated and are completely functional.
I would like to know, why this message appears... and also what is the difference between  informs and traps, because I can activate both of the in a router to be sent to the network admin pc.
Thanks in advance.

Answer 1

Hi Marcelo,
the snmp-server enable traps command enables just all types of traps that the IOS version supports.
The message apperes because of this two, which are mutually exclusive:
R1(config)#snmp-server enable traps ospf cisco-specific state-change shamlink interfaceR1(config)#snmp-server enable traps ospf cisco-specific state-change shamlink interface-old% Cannot enable both sham-link state-change interface traps.% Deprecated sham link interface trap not enabled.
It's recommended to only enable the traps you really need.
Informs were introduced with SNMPv2, and they have the same format and purpose as traps.
The main difference is that traps are send in a hit-or-miss fashion whereas informs expect an acknowledge and will be re-send if unacknowledged.
Hope that helps
Rolf