penguin is correct, there aren't any modules that do the Agent side of SNMP. Neither Net::SNMP or SNMP have the needed functions.

Your best bet will be using Net::Server::Proto::UDP and possibly Mon::SNMP and/or Convert::BER/Convert::ASN1 to decode the traps.

I recently spent long and hard looking for a perl based SNMP Agent to no avail. I ended up using the ucd-snmp agent's pass-through capabilities to hand off portions of the MIB tree to perl scripts.

Start with the Net::SNMP module since it's pure perl it shouldn't be to hard to reverse engineer the trap construction.