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Forum Discussion
New Cable modem and IP router scheme
I have a new Netgear cable modem, CM600 to which I added to my home setup with includes a Netgear R6250 router. Prior to obtaining the CM600 my internal network was in the range of 192.168.100.1 - ....
> Replacing what?
Do you ever answer questions, or do you only ask more?
> Well, I agree but the router can be the IP address you define. Why
> won't my network take the configuration that I define my network by?
> [...]
It "can be the IP address you define" unless that address conflicts
with some other entity on your network. Like, for example, a DOCSIS
modem.
> [...] I don't know if the cable modem has a relationship with my
> router but something isn't playing nice.
That "something" is you. You seem to insist on choosing a LAN IP
subnet for your router which would conflict with the standard address
for a DOCSIS modem. Perhaps your previous modem was a different type
(DSL?), or your previous router didn't care, but Netgear routers
generally do care.
> will my LAN IP addressing scheme be defined by the IP address of this
> DOCSIS modem and [its] default address?
Not "defined", but certainly _limited_.
> I have printers on my network that use Google Docs to print documents.
> I don't wanna go thru setting all of that up again but prefer to keep
> my IP addressing scheme.
I don't understand what Google Docs has to do with anything, but
what, exactly, do you expect to need to reconfigure?
> [...] Even though it has an IP address my router doesn't know what
> that IP is, it just receives an internet connection . [...]
I'm not sure that you know what your router knows or doesn't know.
> [...] I don't have to define the cable modem in the router setup.
That's true, but that doesn't mean that the router will (or should)
allow you to use the "192.168.100.*" subnet.
A router does need to run two different subnetworks on the WAN/Internet interface and on the LAN/WLAN interface.
As the 192.168.100.0/24 subnet is the default internal subnet (not only) for Netgear cable modem and cable routers the second R6xxx does automatically change the effective internal LAN subnet as a courtesy (and because it can't act as a router with oth interfaces on the same subnet).
Now the bigger and not discussed issue here is that you have to NAT routers - the CM600 and the R6xxx. Either run your local network only from the CM600 (and reconfigure the R6xxx as a plain wireless access point as per the documentation if possible) or re-configure the CM600 as a plain cable modem/bridge and only establish one wired connection from the CM600 to the R6xxx WAN/Internet port. Now you can re-configure the R6xxx again to that 192.168.100.0/24 subnet. One constraint remains: Should eg. following a power failure the CM600 won't be properly connect and configured by the cable TV company headend the CM600 (and most other cable modem/routers) will locally configure the network to that very same 192.168.100.0/24 network - and the R6xxx will do it's smart-a** re-configuration of the LAN subnet again.
I would opt to go away from this 192.168.100.0/24 network for your LAN once time is permitting to re-configure all LAN devices - yes, it will take some time.
> [...] you have t[w]o NAT routers - the CM600 and the R6xxx. [...]
Any "CMxxx" model is a Cable Modem (hence "CM"), not a modem+router.
(A "Cxxxx" model would be a modem+router.)
antinode wrote:> [...] you have t[w]o NAT routers - the CM600 and the R6xxx. [...]
Any "CMxxx" model is a Cable Modem (hence "CM"), not a modem+router.
(A "Cxxxx" model would be a modem+router.)Shame on me, sorry for the partially wrong idea above - indeed antinode is always right (that's why we have not many disputes here!) 8-)
So the only "loss" is that the CM600 can't be monitored "through" the router while being connected to the R6xxx [W]LAN while the R6xxx has the same 192.168.100.1 address.
Blunt theory, you could consider to change the R6xxx LAN IP e.g. from 192.168.100.1 to 192.168.100.254 - you can safely ignore the previous replies as LAN IP can serve as a router address or default gateway (there is only one exception in IP routing when multiple routers are involved with some IGMP multicast where the address matters). Then ensure the DHCP pool is limited to not including .254 (that will happen automatically) but also remove the .1. But I must admit: This would not help as the computers are connected to the 192.168.100.0/24 subnet, and an attempt to connect to 192.168.100.1 won't be routed to the WAN/Internet side of the router.