SMC Comcast Business Router Configuration

Posted on 2009-06-29
Last Modified: 2013-12-14
There are a number of other posts with similar questions, but none that I found were able to help me.

When you get a business line from Comcast they give you an SMC router/firewall/modem. Before switching to Comcast business, we had a SonicWall firewall configured and working perfectly for our previous ISP. It allowed inbound terminal services to our terminal services server and OWA (http/https) connections to our exchange server.

Now that I have to place this SMC router in front of the firewall, I'm in a situation where getting the double NAT'ed firewalls working is not as simple as I had hoped.

I know the setup below is wrong because although I have internet access from behind the SonicWall, I can't get in from the outside using services that previously worked (OWA and terminal services).

Comcast wrote down two IPs on the work order:

So this is my setup on the SonicWall:
WAN: NAT-Enabled Static IP:


Static IP Block
"Firewall for True Static IP Subnet Only" disabled
"Gateway Smart Packet Detection" disabled
"Static Routing" disabled
"Port Forwarding" disabled
"1 to 1 NAT" disabled is in the DMZ (I was trying to achieve a "bridge-like" mode even though this device doesn't have a bridge mode)

When I check my public IP from behind the SonicWall, it's currently

What do I need to change for this to work properly?

Question by:DVation191
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LVL 32

Accepted Solution

nappy_d earned 500 total points
ID: 24744412
Did Comcast provide you with any public IPs for usage?

Does the SMC device have any ethernet ports on it?  If so, try configuring your sonicwall with one of the public IPs and connect it to the LAN port on the SMC box.
LVL 20

Author Comment

ID: 24744555
Well the smc gateway has an ip of .206, I;m supposed to be using the .205 address, as we've paid for a static IP.

The SMC does have ethernet ports on it - 4 to be exact. If I configure the SonicWall's WAN IP as the .205 IP, what do I use as the gateway?
LVL 32

Expert Comment

ID: 24744616
Use the .206 as the gateway.  This gateway is not for the SMC device but your ISP's gateway for the internet.

Connect your Sonicwall unit to the etheret port located on the SMC device.
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LVL 20

Author Closing Comment

ID: 31597886
Thank you!
LVL 11

Expert Comment

ID: 24747379
One major Issue:
The part that your sonicWall has a WAN ip of and a Gateway of is wrong. You can never have that. Meaning the Gateway and IP of the device have to be on the same network.
Issue Number 2: you mentioned that: is in the DMZ (I was trying to achieve a "bridge-like" mode even though this device doesn't have a bridge mode) and 1 to 1 NAT" disabled
So what is your internal IP address of sonic wall? How does it communicate with the gateway you provided? Like I said they have to be on the same network for them to talk to each other. there needs to be some sort of a translation or NATing. (your issue number 2)
I just gave you list of things that are wrong but I have not provided any solution. So answer these questions so I can give you some more help. Which device acts as the DHCP server? Which device does the NATing? May be you can disable the NAT on your SMC device and make it act like a layer 2 bridge (roughly).
Let me know
LVL 20

Author Comment

ID: 24747414
Setting the WAN IP on the firewall to .205 and using .206 as the gateway (the smc device), I was able to get an internet connection working with .205 as my public IP. My internal addresses behind the firewall are using 192.168.40.x, but that doesn't seem relevant. Everything seems to be working now.
LVL 11

Expert Comment

ID: 24747443
So what is it that you are looking for? What are you trying to fix that doesn't work?
LVL 20

Author Comment

ID: 24747462
Everything works now - that's why I closed the question and awarded points =)
LVL 11

Expert Comment

ID: 24747545
Oh, damn LOL
I didn't see that you closed it. Well, good luck

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