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[Discuss] Changing Comcast Modem to Bridged

A couple years ago we changed to comcast as our ISP and 
incorporated their modem into our network topology providing 
the dhcp, NAT and wireless functions.

Prior to this we had a DSL modem and WRT54G running tomato. 
The modem provided dhcp so it was the gateway address.

I now want to put the Comcast modem in bridge mode and have 
my wireless router running dd-wrt provide the dhcp and NAT 
for the wireless and wired LAN.

According to the research I've done there are only two ip 
address options for setting up the modem in bridge mode. or

My current network subnet mask is for the dozen or 
so devices that have static IP's. I do not provide any 
services outside the local LAN but within I have a backup 
server that serves a number of devices.

As I understand it the modem IP in bridged mode wants to be 
on a different subnet that the internal LAN which would lead 
me to believe that the 192 prefixed IP address would be the 
choice, this is question #1

Once I've setup the modem with the correct IP then will the 
router now become the gateway?

I have the Cisco DPC3941T modem, has anyone on here set up 
the bridge themselves, I see the option in the management 
GUI, or per my web searching this change can only be done 
correctly by the right Comcast personel remotely?

Well that's the gist of it, did I leave out anything?

Jim Kelly-Rand
jbk at

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