Confused about D3G bridge mode (pass-through) - is a static IP required?

I read in the forum:

"If you want to use ‘true bridge mode’, please note the following characteristics of devices in bridge mode:

Does not have router capabilities or support LAN DHCP
Cannot have a fixed Static IP assignment"
-- Comcast_John 12-15-2014

And other posts stated that only Comcast Support could turn on "true bridge mode".

But today I called Comcast support and asked them to set my SMC D3G-CCR to bridge mode, and the responding tech said that it required a static IP. So I authorized the upgrade, she set the D3G to pass-through, and all's well, using a SonicWall TZ105 as the NAT/firewall and VPN endpoint. The WAN address is set to the static IP. She didn't seem to be all that knowledgeable, and for example, didn't think I could still address the D3G at 10.1.10.1, which I can. So I'm not sure I was given the right advice. I don't have a business reason to have a static IP (I use DDNS) and I don't want to pay the extra charge if I don't need it.

So my question is this: is a static IP now required to set a D3G to pass-through, or was I misinformed?

My preference would be to set my firewall as a DHCP client on the WAN side and have it pull a public IP through the D3G. Or maybe replace the D3G with just a modem, since I'm not using it as a NAT or firewall.

Thanks in advance for your informed answers.

Responses

Accepted Solution

VBSSP-RICH

Advocate

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1.4K Messages

9 years ago

Hello CarrJonesInc and welcome,

The definition of "True Bridge Mode" (TBM) is when your Comcast or any other Industry Gateway's (CIG) router LAN DHCP Server, NAT functionality, StaticIP functionality, is totally disabled. So this means that whatever Firewall, Controlling Router (FW.CR), etc. you have connected will ONLY be able to obtain the CIG's Wide Area Network ((WAN) IP address. Some CIGs will provide your a 3-5 range of WAN DHCP addresses for use by your FW,CR router for networking allocation and provisioning. Again, you cannot use any StaticIP address(es) when your CIG is in TBM because all routing is disabled.

The definition of Psuedo Bridge Mode (PBM) or synonomous PassThrough (PT) is when a CIG has its internal LAN DHCP Server disabled only. This allows full StaticIP routing where the (CG) WAN address is the StaticIP Gateway Address with its respective StaticIP Subnet Mask. When any CIG LAN DHCP Server is disabled this means that the internal built in router will no longer provide any dynamic IP addresses to any device directly connected to any available CIG LanPort. PBM and PT is a good way to avoid any and all conflicts between your FW,CR internal DHCP Server and the CIG Internal DHCP Server. This would also be true if your had any Web Server that has Clients connected and uses its specific internal DHCP, etc.

Hope this helps you out.

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Accepted Solution

VBSSP-RICH

Advocate

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1.4K Messages

9 years ago

You can enable your CG LAN DHCP server while still using your StaticIP. No CG can have a StaticIP and be put in TBM because the total routing in the modem is disabled in the CG when in TBM. Comcast does not support any Comcast Static IPs on any Customer Owned Modems (COMs).

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CarrJonesInc

New Contributor

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4 Messages

9 years ago

HI Rich, and thanks for that explanation. I'm reading into it that the Comcast tech set my D3G CG into PBM, and that a DHCP request from my CR or an offer from Comcast won't pass through PBM, which is why I need a static IP.

I'd still like to go back to a dynamic IP if possible (to save money). Do you know if the SMC D3G-CCR can be put into TBM and pass the DHCP request & offer through? If not, I'm assuming I could just replace the CG with a simple modem that would work with dynamic IP. Is my thinking correct?

Thanks again for your help.

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CarrJonesInc

New Contributor

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4 Messages

9 years ago

Thanks again, Rich. Sometime it's tough to distinguish between actual technical issues and Comcast policy. My plan going forward is to buy our own Customer Owned Modem (probably Arris) and go back to a dynamic IP from Comcast. The WAN port on my router/firewall will be set as a DHCP client and request an IP from Comcast through the COM. Just confirming - this is supported by Comcast on a business account, right? This is the setup I have on my Xfinity residential and it works fine.

To be clear, I prefer a dynamic IP, and only authorized a static IP because the Comcast tech said I needed it for bridge mode or pass-through (for my SonicWALL VPN). She did not offer setting my Comcast Gateway to True Bridge Mode with the dynamic IP, and said it would only work with a static IP. That's what prompted this question in the first place.

This will be the last question, and thank you again for sharing your expertise.

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VBSSP-RICH

Advocate

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1.4K Messages

9 years ago

Just wanted to close out on your last question:

"The WAN port on my router/firewall will be set as a DHCP client and request an IP from Comcast through the COM. Just confirming - this is supported by Comcast on a business account, right? This is the setup I have on my Xfinity residential and it works fine."

Typically, if your Comcast Gateway (CG) or COM is in TBM, then all routing will be disabled. The only routing would be that your CG or COM WAN would use a DHCP address. This WAN address would be provided to your FW or controlling router for interconnectivity to the Internet. Now your internal DHCP server would still dole out dynamic addresses through the WAN address.

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