"To err is Human"
These errors have visited during my compilation, I made a log here so to save my time, if they visit again...
multiple type in same declaration
This error you get when you forget to enclose ; after your class definition.
undefined reference to `Agent::Agent(packet_t)'
This error you get if you dont follow the step
mentioned in nsrthowto. This is because you have modified only .h file without modifying .cc file.
You need to tell your compiler to recompile the packet.cc explicitly, I believe the gcc compiler is clever enough to recompile the modified .cc files, but it may not track the .h files.
(Sorry for my English).