Well I solved the using by using the opening the custom game and then executing the connect ip address command on the pc.

But I When I join my friend over offline lan in custom game,it always opens up as spectator mode.How to make this double player against zombies.

While connecting me and my friends laptop over same wifi and creating clicking on Public Match on one laptop and using console to type "connect 192.168.43.51:4976" its not connecting.Also its not even showing the name of other pc.
On the other command prompt window its just showing "Received CL OOB 'getchallenge' from 192.168.43.51:4976"
I am using the latest Plutonium r372