I wanted to know if the components are distributed across the network and if the server is behind the firewall, what issues would arise ?
EJBs do not communicate gracefully through firewalls. A typical firewall will only allow communicate on port 80 and 443, and EJBs need (at minimum) port 900 and possibly other ports.
You can either:
1) Monitor network traffic and open enough ports to allow your EJBs to communicate (this will make your security folks unhappy).
2) Use web services, which communicate over port 80/443.