What does your infrastructure look like?
I assume:
ISP >> ISP's Cable Modem >> Wired Switch >> Computers
You have a few choices, depends on how advanced you want to get. The issue with these devices is that they combine a modem and a router/firewall into one device.
Do one thing and do it well vs. be mediocre at many things.
I have that same SMC modem in a few places and I ask the ISP to put it into BRIDGE mode. This allows the device to only act as a modem, not as a combo modem, router and firewall. I normally put them into bridge mode, connect port #1 to a proper router/firewall then to a switch from there:
ISP >> ISP's Cable Modem (in bridge mode) >> Firewall/router (I use pfSense or Juniper hardware) >> Wired Switch + separate wireless appliances >> Computers
You have a non-managed switch and a modem trying to route. It's proper and legit for a home type network but if you rely on it for trading I'd change it over to something else. Even a Linksys WER54GS (GET THE S) 10/100 router with the wifi turned off and running dd-wrt would work well (assuming your ISP connection is less than 100mbps). Let your modem be a modem, let a router route and push DHCP addresses and let a switch switch traffic.
I also use Linksys/Cisco WRT310N running dd-wrt. If you turn off the wireless the routers CPU is very overkill for just a simple one port WAN one port LAN router.
On the router, set each computer to a static IP, not at the machine, at the router. Use the port on the motherboard for the NIC so you can access Wake-On-Lan features and simplify everything.
