Re: home lan setup suggestions

Ragga <look@xxxxxxxxxx> writes:

1st config- modem is set to pppoe-bridging with dhcp on (in pppoe mode
it can't be turned off) , router's internet connection dialog set to
Router internet config dialog shows:
Connection : Auto-dhcp
IP address :
Subnet :
Default gateway : , being the IP assigned by ISP
Modem manages the connection/disconnection to internet, being still
accessible trough browser at (this puzzles me because i
though it wasn't going to work, since router's gateway is set to
another ip)

The router itself uses the gateway IP given to it by the ISP. It uses
it as the default next hop it's gonna send outgoing traffic to on the
WAN interface. Your LAN devices will use your router's IP as
their default gateway.

That is what I don't understand, see if this makes sense.
Router's gateway should be the modem, and modem's gateway should be
the ISP's, so router dialog should tell me its gateway is .
This is what happens if I unplug the phone cable from the modem: no
internet connection, no assigned IP from ISP, router tells me its
gateway is, very reassuring.
Then I plug in the phone cable, modem hooks up with dsl signal, gets
its dynamic IP .
At this point router changes the parameters shown, and tells me
gateway is .Same scenario as above.
If I traceroute traffic, it shows the obvious - - ISP machines - whatever route to target.
This makes total sense.
So where is What is that?
The only idea I can come up with is "dynamic Ip + 1" is the address
assigned by modem's dhcp to router's wan port in the mini-lan
connecting the two devices.Mini lan that should be the 192.168.0.X
subnet (thus I am able to access modem config with browser, pointing
it at, while my pc's+router lan is the 192.168.1.X
Still router should tell me its gateway is as shown in the
Router's gateway address is router's wan port IP?
Modem's IP (on my side) is both and (this
makes no sense at all)

What make/model of router and make/model of modem? I'm having
trouble picturing where you're seeing this .50 and .51 address. If
you can search up a screen shot or something on the internet it might
be helpful to answer the question.

Generally with a cable modem, teh routing goes
1 your home router's LAN IP
2 an IP somehwere in your ISP's network
3 other stuff

The IP your cable modem is assigned doesn't show up, since strictle a
cable modem isn't an IP layer device. It' conencts at one layer lower
on the ole network stack. From a IP standpoint, the cable modem is
really just a layer 2 thingee that connects your home router to the
ISP's network, and IP doesnt' care about the details.

Once you get the IP and everything is trained up and working, visit a
site like (which provide the IP address as
internet web servers would see you as being) and compare those with
what you're seeing on these various screens.

In my case (which is similar router+cable modem), my "public ip" as
webservers see me (and as I'd see at a or
equivalent) matches the "WAN IP" I see in my home router's
configuration page. This address doesn't show up in a traceroute (as
it's not a router's IP address). The default gateway, from the
perspective of my home router is an IP address within my ISP, and it
matches to the IP I see on the 2nd hop of a traceroute performed from
any computer inside my LAN. The first hop of course is the internal
IP address of my router.

Now, on the cable modem itself.... (as reported at the DOCIS standard
location of on my scientific atlanta cable
modem) the "cable modem IP address" shows a 10.x address that shows up
nowhere else (not in my router, not in my traceroutes, etc). And
under "CPE Conenctions" on this cable modem status web page, my public
address (that one that matches does show there.

Finally, on my client machines in my lan, all DHCP assigned machines
have my router's internal LAN IP address as their default gateway.

Dunno if any of this helps you directly, but gives you another common
datapoint to see if you can figure out what the various IP addresses
that you're seeing on your network can be made sense of.

Todd H.

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