I've done a search here and wasn't able to find anything relevant to my situation. I apologize in advance if I've missed an existing post on the topic.

Our ISP has provided us with 6 static IP addresses. We are currently using two of them (plus one for the Comcast-provided router). One of the static addresses routes to our internal network, and the other goes to our VOIP phone system. Unfortunately, the Comcast machine doesn't support QoS, so our VOIP calls have been choppy.

We plan to put the Comcast-provided router into bridge mode and replace it with an ASUS RT-N16 running DD-WRT. However, I'm unsure how to set up DD-WRT to function similarly to our existing Comcast router. The Comcast router's WAN IP is the first of our static IP addresses. We did not need to provide an internal LAN IP address — simply connecting machines that use our other public addresses to the LAN ports on the Comcast router is enough for it to route between the connected machines and our internet connection.

Is there a way to do a similar setup through the DD-WRT?

Thanks in advance.