I think your question is not clear. The router doesn’t filter internal traffic (at least not by default). All traffic in the internal network will be open by default, since the router simply acts as a switch.
You have to make sure that each machine has the appropriate firewall rules to allow the traffic if it comes from the internal network, but that is each machine’s responsibility. Your router has nothing to do with this.
Remember that the router routes traffic between one network an another, but not within the same network (unless you create DMZs and/or have an advanced network or networks).
Maybe if you expand your question a little bit more, indicating what is exactly what you want to do (and what happens now), we could give you more help.