|I'm still not sure what your problem is. |
A typical small business setup is as follows:
Internet >> SOHO Router >> Switch(es) >> Clients
If you use the DHCP server service provided by the SOHO Router for client TCP/IP settings, then they will have both LAN and Internet connectivity.
The same is true for larger environments but you might have an actual separate firewall device and then an enterprise level router through which all external traffic flows. You would have an internal DHCP server which once configured correctly, would provide TCP/IP settings to clients allowing them both internal (LAN) and external (WAN) connectivity.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.