Using D-Link DIR-655 with Comcast SMCD3G-CCR

[SeanMay]

OK, so, I'm sort of the de facto IT guy for my office and I've run into an issue with hooking up a D-Link DIR-655 to the Comcast Business gateway (model SMCD3G-CCR). I've done networking stuff in the past, but this is maybe a little over my head. We want to use the D-Link for wireless since the Comcast gateway doesn't have it. Comcast told me that it would be as simple as hooking the router up to the existing gateway and there'd be no issue...well, then reality reared its ugly head and killed that notion.

Here's a rough version of how we're set up: The Comcast gateway has 4 ports, and I think is acting as a router and a modem. Currently, 3 of the ports from that gateway go to what I think is an unpowered switch (it's a board with 12 ethernet ports on the front...here's a picture:


The other port goes directly to another PC.

We also have 4 IP phones downstream of everything, but I don't think they'd affect the situation.

What I have tried so far is that I took one of the ports from the gateway and connected it to port 1 on the D-Link, then hooked another cable to port 2 and then hooked it into the switch, more or less adding the D-Link to the loop. The good news is that everything appeared to work fine, we were able to see the wireless signal, access the internet through it, and the wired computer that was routed through the D-Link was working correctly.

Then the problems started...

First off, I'm not able to access the router to enable a wireless key. The router is assigning IPs in the range of 10.1.10.xxx, and the Comcast admin panel shows me everything connected, and the router doesn't show up. I even tried just manually putting in IPs in that range to see if I could find it, but I had no luck.

Secondly, after a while, connections started to go down. One of the computers, not the one hooked into the D-Link, lost connectivity completely and the IP phone in that office displayed "Searching for DNS". I was only able to fix this by completely removing the D-Link from the network entirely, leaving us without wireless.

OK, I hope that makes some sense, and I hope someone can help me. Thanks in advance!

[YeOldeStonecat]

You have 2x approaches...to flip your DLink router into basically a wireless access point.
Or...the approach I use for my clients offices setup on Comcast business...I use my clients own router as the only router, and set the SMC gateway to pass the public IP to the WAN interface of my clients router.

Since you have an SMC Gateway from Comcast..you probably have a static IP from them. They should have written down that info when they set you up...you'll have the static IP range, subnet mask, gateway, and DNS. If you don't have that..call them..they'll give it to you. Ask them what your first usable IP is (or just post here asking..but I'm not available again until Monday).

Now...plug a computer into your DLink...log into its web admin, setup your WAN interface to static IP..and enter that info. Now..uplink the DLinks WAN interface to one of the LAN ports of the SMC. Next...plug a computer into one of the other LAN ports of the SMC..and log into its web admin at 10.1.10.1 username cusadmin password highspeed or visa versa.
Go to the firewall tab...look around, there's a checkbox for "Disable fireawll for true static IP subnet" ....put a check in that...apply/save....and reboot the SMC. After a minute goes by...reboot your DLink. Now...plug computers into the back of your DLink....surf the net. Go to whatismyip.com and check the IP..should be the IP that you typed into the WAN port of the DLink. So now the SMC is basically routing (passing) that public IP you entered to your own router without any firewall/NAT features.