but here another question, how can i access a specific host in a local network through the router?, because the public IP is the IP from the router not of a host in the network, can i do this?
Well first tell me what do you mean by public ip is the ip from the router not of a host.
if there is a router then its not your local domain.
there may be some subneted network and you are must be in one of them.
but still you can access other domain host if you its ip.
no big deal.
first check out your main network topology.
now if you don't know about host ips then first scan for active router, thats how you will get ip of router then scan for particular network in which your target is.
then get access to if if you know the password