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Can I use a C6300 cable modem without cable internet?

clamage45
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Can I use a C6300 cable modem without cable internet?

I switched from cable internet to AT&T Uverse. The AT&T router does not seem to have as strong a 5Ghz signal as the C6300. Can I use the C6300 as just a router without a cable connection? It doesn't have a LAN input port, but is there some other way to get it to act like an ordinary router?

Model: C6300|AC1750 Cable Modem Router Docsis 3.0
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antinode
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Re: Can I use a C6300 cable modem without cable internet?

> [...] The AT&T router [...]

   Not a very detailed description of anything.

> Can I use the C6300 as just a router without a cable connection?

   Not really.  Without an Ethernet WAN/Internet port (or a cable-TV
ISP), its router functions are hidden.


> It doesn't have a LAN input port, [...]

   Eh?  What's "a LAN input port"?  What it doesn't have is an Ethernet
WAN/Internet port.

> [...] but is there some other way to get it to act like an ordinary
> router?

   Not as a router, but, if you like its wireless capability, then you
may be able to press it into service as a wireless access point.  It's
not a trivial procedure, but should be possible.

   Basically, you want to ignore the router's WAN interface, disable
its DHCP server, and make its LAN parameters compatible with the LAN of
the real (full-function) router (your (unspecified) "The AT&T router").

   Ignoring the C6300 WAN interface is easy, because it's hidden behind
the cable-TV hardware.  To disable the C6300 DHCP server: ADVANCED >
Setup > LAN Setup : [ ] Use Gateway as DHCP server.  The C6300 LAN
parameters should be on that page, too.

   Some changes may be desired on your (unspecified) "The AT&T router",
too, but, knowing nothing about it, I can't offer many details there.

   The following (untested) procedure might serve as a guide.

   0. Gather information on the main router.  Connect a computer to any
LAN port on "The AT&T router", and deduce the LAN address of that router
from your computers gateway/router address, or, find it on that router's
web interface.  Let's say that it's "192.168.X.1".  You'll want to
configure the C6300 LAN interface with a similar-but-different address
on the same subnet; let's say "192.168.X.250".

   1. Prepare to configure the C6300.  Disconnect the computer from "The
AT&T router", and connect it to any LAN port on the C6300.  Use a web
browser to access the C6300 web server management interface
("routerlogin.net", "192.168.0.1", or whatever).  (It might be possible
to do this with a wireless connection, but it would add more
complications.)

   2. Change the C6300 LAN IP address to "192.168.X.250".  ADVANCED >
Setup > LAN Setup : LAN TCP/IP Setup : IP Address.  The C6300 should
want to restart; when it recovers, it should use its new LAN IP address,
"192.168.X.250".  You may need to restart the computer, too, for it to
adapt to the new address of the C6300.

   3. Re-establish contact from the web browser to the C6300.
"routerlogin.net" may or may not work now, but the new address,
"192.168.X.250" should.

   4. Disable the DHCP server on the C6300.  ADVANCED > Setup > LAN
Setup : [ ] Use Gateway as DHCP server.

   5. The C6300 should now be ready to act as a wireless access point.
(It's now too stupid to do much else.)  Disconnect the computer from the
C6300.  Connect an Ethernet cable from a LAN port on "The AT&T router"
to a LAN port on the C6300.  You should now have one big LAN (subnet:
"192.168.X.*"), and devices connected to either "The AT&T router" or the
C6300 should be able to communicate with each outer and with the outside
world.  Connect the computer to either "The AT&T router" or the C6300,
and verify that (see if?) things work as expected.

   In this configuration, the C6300 acts as a simple network switch
(with wireless capability).  "The AT&T router" does all the serious
work, like providing DHCP and DNS service to the (newly extended) LAN,
and handling connections to the outside world.  This means that the name
"routerlogin.net" (and its friends) will no longer work.  (Only the
C6300 knew about it, and the C6300 won't be used for DNS.)  If you want
to talk to the C6300, you'll need to use its (new) address,
"192.168.X.250".

   At this point, a web browser on any computer, connected to either
"The AT&T router" or the C6300, should be able to get to the C6300 web
server (at "192.168.X.250"), which will let you do things like configure
its wireless network settings.  (And everything else on the LAN should
work as before.)

   6. Adjust the DHCP pool on the main router.  The C6300 (LAN
interface) now has a static IP address, "192.168.X.250", assigned in
step 2.  The main router ("The AT&T router") is unaware of this, and if
".250" is in its DHCP pool, then there's a chance that it will offer
that address to some other (DHCP client) device, which would cause
problems.  In a typical Netgear router, the default DHCP pool covers
".2" - ".254".  If "The AT&T router" is similar, then an easy adjustment
would be to shrink the pool range to, say, ".2" - ".249".  The only
requirements are to get the C6300 LAN address out of the pool, and to
leave the pool big enough to handle all the clients which will be
connected to the LAN.

   What could go wrong?

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