Equipment (Modems,Gateways)
Modems, Gateways, and Networking Devices
Male IT Specialist Holds Laptop and Discusses Work with Female Server Technician. They're Standing in Data Center, Rack Server Cabinet is Open.
Highlighted
New Contributor

Bridge and Static IP Confusion

Confused by what I am reading.  I am reading that if I have a static ip from Comcast, I can not have a modem in bridge mode.  I need to have my modem in bridge mode and connected to my own firewall device.  The static IP would be on my firewall as the public IP.  This is what I have been trying to accomplish with Comcast tech support.  Still does not work correctly.  Tech support has not said anything about this not being possible.

 

I had this before with AT & T and at home.  Is my set up at work not possible?  Would my problem be solved with purchasing/renting a modem only approved device, such as a SB6141?

 

Thanks.

0 Kudos
4 REPLIES 4
Highlighted
Occasional Visitor

Re: Bridge and Static IP Confusion

In my experience, you get a router address (assigned to the router by Comcast) and the static IP.  Set the IP of the device you want to the static IP, and set its gateway to the router address.  The router will handle the routing.

 

Yeah, it is kind of a weird system...

0 Kudos
Highlighted
New Contributor

Re: Bridge and Static IP Confusion

Thanks for your answer.

 

I am thinking that it might be easier to just get a Comcast approved modem only box and use that. 

0 Kudos
Highlighted
Trusted Forum Contributor

Re: Bridge and Static IP Confusion

Hello awrych,

 

There is no reason whatsoever as to why you cannot purchase a staticIP from Comcast, then have it  loaded and configured on your Comcast Leased Gateway (CLG), then you program your routable static IP address, gateway address, and subnet mask onto your firewall/controlling router, then lastly disable the CLG internal DHCP server that puts these into pseudo-bridge mode. There are currently thousands of Comcast Business Class customers successfully implementing this with consistent functional operation.

 

Hope this helps you out.

0 Kudos
Highlighted
Occasional Visitor

Re: Bridge and Static IP Confusion

I wouldn't worry too much about bridge mode and purchasing your own equipment. The Comcast box handles it all automatically, and in fact there is nothing to configure and no manual way to set it (which is confusing in its own way).

 

Connect your firewall WAN interface to one of the LAN ports on the Comcast box, configure your firewall with a static IP on the WAN interface, reboot everything, and you should be all set. 

 

First thing to double check is your firewall WAN configuration. Comcast will provide you with a range of static IP addresses to use, along with a gateway IP, which is typically the next IP address higher than the range you are assigned. For example, if you have one static IP that ends in .129, the gateway would generally be .130. If you have a range of IPs from .129 to .133, your gateway would be .134. You'll need the right subnet mask also… usually 255.255.255.252 for one static IP or 255.255.255.248 for five.

 

Something optional that I tend to do is to go into the modem's config panel (http://10.1.10.1) and disable the firewall for "True Static IP mode." All this does is disable the firewall for static IPs, and it has no bearing on the use of static IPs, but it can eliminate a point of confusion by taking Comcast's firewall out of the picture network-wise.

 

The last thing I suggest is to reset the devices after you change hardware or IP address configurations. When you're fiddling with things, the Comcast box can lose track of what goes where because its ARP cache is stale. Resetting the cable modem will refresh that.

 

But the bottom line is, you do want the box Comcast provides, you do not have to buy your own modem, you can ignore the built-in switch and firewall on the Comcast box, and if you configure your firewall for a public static IP, the Comcast box will automatically switch into bridge mode and do the proverbial right thing.

0 Kudos