Reconfigure Comcast Business IP Gateway so can use own router

I currently have a Comcast Business IP Gateway, SMC8014, connected to a switch with multiple PCs.  I want to add wireless so I want to add my own wireless router (using a Netgear WPN824).  Thus I need to reconfigure the Comcast Cable Modem/Router to act just as a Cable modem.  I have accessed the Comcast SMC8014 and have all the current settings.  Then I need to configure my router. So here are my questions:
1.) What do I need to all turn off or disable in the Comcast Modem/Router?

2.) What IP address do I need to use to configure my new router?  The modem and router each have to have their own IP address correct?  I'm assuming I got a Static IP from Comcast, the IP address to access the Comcast Gateway is  But what is my static IP (how do I tell)? Which page in the config area do I need to look at, eg. they list under Internet Settings:  WAN DHCP IP Address, WAN Internet IP Address, Static IP Block, and under Local Settings: Gateway IP Address, IP Range Start, etc.

3.) What is a public static IP address?  They talk about public static routable IP addresses vs. private static IP address.

Joe B.
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API_NOCConnect With a Mentor Commented:
Joe B,
This is a one-shot post, so good luck.  
1. Unless Comcast can convert their equipment into bridge mode for you, it looks like it cannot be done.  From what searching I've done on the Internet, it is not possible to change the router you have into a bridge because of the non-standard code on it.  Even if they are capable of changing the equipment to bridge mode, you will have to still follow some of #2 and #3 below.
So just go with one of these:
2. To simply accomplish your requirement, you can plug the Netgear into one of the LAN ports of the SMC and configure your wireless.  Now in order for you to have all of your PCs and wireless on the same network, ALL of your devices would have to connect  to the LAN ports of the Netgear, AND NOT the SMC.  This is doing a double NAT, but that's okay, because you want to have wireless.
3. To avoid the double NAT, and so that you know who to call if your Netgear fails and you can no longer surf the Net, then you can use this configuration.  Log into the Netgear and turn off DHCP.  Make the LAN ip of the Netgear something that is on the same network as the SMC, but do not use an ip address that is already in use.  For instance, you can possibly make the ip address of the Netgear LAN, mask and gateway of  Now you can connect the Netgear LAN (one of the switch ports) to the LAN of the SMC.  You will not have to change any ip addressing on your existing equipment, and your new wireless devices will connect to the same network that you have.
Michael WorshamConnect With a Mentor Infrastructure / Solutions ArchitectCommented:
The Comcast Business IP Gateway (SMC Unit) does not have a 'bridged' mode as per se. Instead, you have a couple of choices to use instead...

1) Setup Static Routing for each of the available IPs they have assigned you. The Comcast user guide (which I have attached) explains this a bit more in detail.

2) Turn off all the filtering, DHCP and NAT/PAT functionality built into the SMC, assign one of the static IPs to the WAN interface of the router and then treat it as the default gateway on any machine that you want to assign one of your public IP's. Plug in a switch on one of the LAN ports then setup your internal network based off this switch (see code snippet for quick diagram).

Also check these reference threads/sites for additional needs:

5 port switch (you supply)
+---- first computer / server with IP set to one of your static IPs
+---- second computer / server with IP set to one of your static IPs
+---- third computer / server with IP set to one of your static IPs
+---- fourth computer / server with IP set to one of your static IPs
+---- Wireless router w/ DHCP enabled to handle other "user" computers

Open in new window

With that kind of configuration, why have a "firewall" at all?  My recommendation is more sound to address this request.
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Michael WorshamInfrastructure / Solutions ArchitectCommented:
APC_NOC: Between the SMC and the switch, you could put your own firewall up as an option. I have done this before using the Untangle Application server (in bridged mode) to act as an IDS in between the SMC modem and network switch. You can also allow the Untangle appliance to dole out the DHCP addresses or even one of the internal servers (i.e. SBS 2003) as well if you don't want the wireless router to do so. Works like a charm.
JoeBoydAuthor Commented:
Thanks both of you for you help!  I think I just about have it setup now.  Your explanations helped.  I did find out from Comcast that I don't have a Static IP - the SMC set as modem/router gets a dynamic IP from Comcast.  Here's what I did and I have a follow up question please
1.) I left the SMC set up as the modem/router (DHCP enabled and all the other settings set as was)
2.) Left the Netgear router set as it came out of the box, DHCP enabled, etc.
3.) Connected patch cable from the SMC, Port 1 (a LAN port) to the "Internet" connection on the Netgear Router.
4.) Connected a patch cable from a port on my 16 port switch (where all my PCs are connected to) to Port 1 (LAN port) on the Netgear router, so all PCs are connected to it.
4.) Rebooted all PCs and they all got new IP addresses from the router and on the 3 PCs I tested I have good internet connection.
Do I need to disable the DHCP, or anything else, in the SMC cable modem/router?  Everything seems to be working as is and since the only thing connected to the SMC is the router I wouldn't think I'd have to??? But I'm not sure.
You do not have to disable DHCP.  It is fine the way you have it set up.  Note that by not changing anything on the SMC will help you whenever there is a service call that goes into Comcast.  They will (should) have a record of your trouble calls, and make notes of what was changed.  This way, you can save time on the phone with them.  So if it ain't broke, then don't try and fix it.
One additional note as to why you should leave it as is.  Suppose you lose your internet connection (from behind the Netgear).  You could then take a PC and connect it to the SMC, thus bypassing the Netgear.  If you can browse, then you know the issue is with your Netgear.  If you cannot, then you know that there's an issue with the circuit/connection or with the SMC.  In this scenario, it would be on Comcast to address the issue.
Michael WorshamInfrastructure / Solutions ArchitectCommented:
Honestly, in my opinion, I wouldn't have two DHCPs running as it could cause headaches down the road. I would disable the DHCP on the SMC and give it an internal static IP address (along with the other LAN ports that it houses), then allow the Netgear router to connect to just that one static IP address (i.e. it's gateway) and dole out DHCP IPs for the switch that is connected to it.

The only other thing I would note is that if you plan on running some sort of 'server' from behind the Netgear, you really won't be able to as the SMC nor the NetGear don't have a setting for 1-to-1 NAT routing. The work around would be to just hook up the 'server' to one of the extra LAN ports on the SMC, give it a static IP address and use port forwarding from the SMC to the server for whatever your needs are.
JoeBoydAuthor Commented:
Thanks both of you.  You both helped a lot so it was hard deciding on which answer to pick entriely.  I think API NOC did a better job in my case helping me with the more direct solution, but mwecomputers also helped in my learning more about all this stuff.  Thanks again.
Comcast just installed a business class line for me with 5 static IP's and a SMC8014 modem. I wound up finding this thread as I also was wondering how to get to my static IP's given the router was doing NAT. On a whim I just tried assigning my computer one of the static IP's (along with the specified gateway, etc) and it worked!

So, it looks like at least the current versions of the router are set up to provide a NATed address if you use DHCP as well as routing the static IP's if you assign them manually.
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