OMNET++ is pretty good.  Visit the following link:

https://omnetpp.org/doc/omnetpp/tictoc-tutorial/ 

Thank you so much. 

Dear Mahfujur

         As mention previously by Amena , OMNET++ is good to use now as we are expecting good development and support in terms of packages in future. 

       There are example scenarios in OMNET++ packages / modules where the code of MPLS , OSPF is available just have it and simulate. 

Dr Adnan

https://inet.omnetpp.org/

Dear Dr Adnan,

Thank you so much. 

Mahfuj 

Hi,

My advice is to not start with the inet modules as they are quite difficult for beginners. First, start with samples from Omnet such as 'routing' to understand the global architecture of Omnet, once you feel comfortable with it you could try the inet modules.

Good luck

Dear Mahfuj,

Omnet++ is good to go, however, as Mutapha Reda indicated proceed systematically as still as for now there are small number of omnet experts and help out there. If you stuck with a problem you have to spend lot of time just to understand it. However, you are good to go if programming skills are good and get hands on omnet tutorials. 

For IP Networks Cooja with contiki might be more specific. 

Best luyck