DSL modem's IP must be outside the router's subnet?

[John Hupp]

It seems to me that I have previously had a DSL modem at 192.168.0.1 and an
Ethernet router at 192.168.0.2, but right now that won't work for some
reason, and I'd like to understand why.

My DSL modem is an Efficient Speedstream 5100 ADSL (several years old) with
hardware PPPoE auto-logon. It has no firewall/router, and is set at the
factory default IP of 192.168.0.1.

(I don't know if it's relevant, but there is an advanced modem setting thus:
"A very limited number of applications require that the public IP address
assigned to the modem be used by the local LAN device. Let LAN device
share Internet address?" The current selection for that setting is "Yes,
use public IP address." Regardless of that, the WAN side IP of the modem is
a public IP (70.224.xxx.xxx) and the LAN side is 192.168.0.1.)

The current router is a NetGear FM114P (802.11b + 10/100 Ethernet,
Firewalled, with Print Server) with WAN-side IP assigned by ISP, DNS servers
assigned by ISP, and LAN-side IP set to 192.168.1.1 (with DHCP pool
beginning at 192.168.1.2).

If I instead set the router's LAN-side IP to 192.168.0.2, with the DHCP pool
beginning at 192.168.0.3, I get no Internet even though there is no IP
conflict. And I can't ping a known DNS server's URL.

Can anyone educate me a bit?

--John Hupp

 

[Jack \(MVP-Networking\).]

Hi
Your Modem is a Modem/Router combo and thus NAT firewall by default. If it
was not a Router your IP toward the LAN would be the External IP, and the
PPPOE would not be initiated by the modem.
Changing from the Internet address to the 192.168.xxx.xxxx is called
Routing, thus the device is a Modem Router.

Since it is a Router your Netgear has to be connect as a switch with printer
server.
Like this,
http://www.ezlan.net/router_AP.html
If you do want Network segregation then connect the system like this,
http://www.ezlan.net/shield.html
Jack (MVP-Networking).

 

[Steve Winograd [MVP]]

It seems to me that I have previously had a DSL modem at 192.168.0.1 and an
Ethernet router at 192.168.0.2, but right now that won't work for some
reason, and I'd like to understand why.

My DSL modem is an Efficient Speedstream 5100 ADSL (several years old) with
hardware PPPoE auto-logon. It has no firewall/router, and is set at the
factory default IP of 192.168.0.1.

(I don't know if it's relevant, but there is an advanced modem setting thus:
"A very limited number of applications require that the public IP address
assigned to the modem be used by the local LAN device. Let LAN device
share Internet address?" The current selection for that setting is "Yes,
use public IP address." Regardless of that, the WAN side IP of the modem is
a public IP (70.224.xxx.xxx) and the LAN side is 192.168.0.1.)

The current router is a NetGear FM114P (802.11b + 10/100 Ethernet,
Firewalled, with Print Server) with WAN-side IP assigned by ISP, DNS servers
assigned by ISP, and LAN-side IP set to 192.168.1.1 (with DHCP pool
beginning at 192.168.1.2).

If I instead set the router's LAN-side IP to 192.168.0.2, with the DHCP pool
beginning at 192.168.0.3, I get no Internet even though there is no IP
conflict. And I can't ping a known DNS server's URL.

Can anyone educate me a bit?

--John Hupp

I'm assuming that you've connected the modem's LAN side to the
router's WAN (Internet) side. For the router to work, its WAN and LAN
sides must use different subnets. If the router's WAN side gets
192.168.0.x from the modem and the router's LAN side is also
192.168.0.x, there's a subnet conflict, and Internet access through
the router won't work.
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

 

[John Hupp]

Thanks, Jack and Steve, for serving up helpful explanations that I can
understand.

--John Hupp

 

[Steve Winograd [MVP]]

Thanks, Jack and Steve, for serving up helpful explanations that I can
understand.

--John Hupp

You're welcome, John.
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com