Cable Modem & Router aren't speaking to each other

[Kaloramabob]

Got tired of paying to rent a cable-modem from Comcast each month, so I bought a Motorola SB6141, which Comcast says it supports. When I got home, I unplugged everything and restarted my network. Now, my Netgear N600 Wireless Router isn't seen by the new cable modem. When I plug my pc directly into the cable modem, I can get to the internet. When I pull the new cable modem out and re-install the old one, I can use my wireless router.

Before I return the Cable Modem (and try something else?) - does anyone have a thought on how I can get these two together?

Thanks.

 

[Elixer]

Assuming you have the router setup correctly, all that is required is, unplug all, then plug in cable modem. Wait for it to get online status, then plug in router, and wait a bit.
Then turn on your computer.

You also had to tell comcast the MAC ID of the new modem...

 

[ch33zw1z]

When I replaced my leased modem with a modem I bought, I had to call Comcast to provision the new modem and give them the hardware ID's. Motorola SB6120

 

[AnonymouseUser]

When I replaced my leased modem with a modem I bought, I had to call Comcast to provision the new modem and give them the hardware ID's. Motorola SB6120

He said it works with his PC, so that's not an issue.

What usually is an issue is the Router not sending the MAC ID to the modem. It's usually an option in the router setup, and can use your current PC MAC or the router's MAC.

 

[Binky]

The cable modem may be locked to a Mac ID. You can try spoofing it. There is usually a setting where you can specify the Mac ID.

 

[Ketchup]

I unplugged everything and restarted my network. Now, my Netgear N600 Wireless Router isn't seen by the new cable modem. Thanks.

Once the modem is set up to your connection, which in your case it sounds like it is, connect your network cables to the powered-down router, then turn it on.

If this doesn't work, reset the router and try again.

 

[wirednuts]

not sure how you got a new modem to work without calling comcast and updating your mac address... unless you were able to set the new modems address to the old one's.

 

[ch33zw1z]

He said it works with his PC, so that's not an issue.

What usually is an issue is the Router not sending the MAC ID to the modem. It's usually an option in the router setup, and can use your current PC MAC or the router's MAC.

Config issues, may as well get it done right.

 

[Kaloramabob]

Thanks for the advise - sorry I didn't mention calling comcast first. I did, and that's when the cable modem began working, if only with my pc! The router will work with the old cable modem, but not the new one. How do find these settings in my router? And what am I looking for?

 

[ch33zw1z]

Thanks for the advise - sorry I didn't mention calling comcast first. I did, and that's when the cable modem began working, if only with my pc! The router will work with the old cable modem, but not the new one. How do find these settings in my router? And what am I looking for?

1. Unplug everything data/power on the modem router.

2. On the modem unplug power, ethernet, and coax. Let it sit for a few minutes, plug the modem coax, then power, then ethernet. Wait for the modem lights to indicate ready.

3. On the router, plug in ethernet from the WAN port to the modem ethernet, and plug in power.

This is the process I go through to swap out the router or modem.

If you still have problems, login to the router via IP and make sure the WAN connection is still DHCP. You could always try a reset on the router.

Were you direct connected to the modem when you called Comcast and went through the setup?

The modem "internal" IP is 192.168.100.1

 

[Cabletek]

Lots of theories, but lots are wrong.

Step 1. power down the modem and the router.
Step 2. connect a PC/Mac directly to the modem.
Step 3. power up the modem.
Step 4. verify you have internet over just the modem off the PC/mac. If you do skip to step 6.
Step 5. call Comcast and have them provision the modem, then return to step 4.
(you must provide modem and HFCMAC or CMAC to them for provisioning)
Step 6. connect the router to the modem and power cycle the modem.
step 7. after the modem ONLINE light goes SOLID, power up the router.
step 8. connect your PC/Mac and other equipment to the router, wired or wireless.
step 9. test for internet, make sure to give the devices ample time to get IP., DNS, etc..

 

[Fallen Kell]

As others have said, Comcast has locked down the DHCP services to the MAC address of the system connecting to it. While you did get them to update the modem, you probably initially just had your PC direct connected to the new modem when you had Comcast set it up. When Comcast did their setup, they tied the MAC address of your PC to that modem and setup their DHCP tables to give an IP address to your PC's MAC. You need to go into your modem and spoof the external MAC address of the WAN port to be the same as your PC's MAC address.

 

[Cabletek]

Comcast has not done anything, you are confused. The cable modem itself learns the MAC of the first device it connects to, and only talks to that device UNTIL you power cycle it, then it forgets and looks for a new MAC. This is indeed the way ALL BRIDGE devices work. Cable, DSL, ISDN, etc. unless a router is embedded making it a gateway, its a bridge and that's how they work. If your not getting a private IP, it's a bridge.

You cannot spoof a cable [modem] mac address legally, it is burned into the eeprom chips. Comcast has no idea what the mac of his PC is and does not care what it is, people get new computers [and other internet devices Blu ray players, tv's, game consoles, etc...] all the time, that would be a costly headache to track. You can spoof the ROUTER's mac, but is not necessary, just power cycle the modem with nothing hooked up or even the NEW router hooked up and it will LOOK for a NEW mac to talk to until it finds one.

 

[Binky]

You cannot spoof a cable mac address legally, it is burned into the eeprom chips. Comcast has no idea what the mac of his PC is and does not care what it is, people get new computers [and other internet devices Blu ray players, tv's, game consoles, etc...] all the time, that would be a costly headache to track. You can spoof the ROUTER's mac, but is not necessary, just power cycle the modem with nothing hooked up or even the router hooked up and it will LOOK for a NEW mac to talk to until it finds one.

Every router I've owned had the ability to change the Mac address. I highly doubt there is any legal problem with that. My current Tomato router firmware gives me the option to use the default Mac, a random Mac, or clone the PC Mac.

Whether the modem resets on power cylcling is the question. In my experience this isn't true. I've had at least one old-ass DSL modem that would just not let go of the old router's Mac after several power cycles and several hours. I just cloned the damned Mac address and left it like that for several years. No problem.

 

[Ketchup]

FWIW, I don't set up routers for a living, but the number of routers I have added/swapped for people is probably in the dozens over no less than 5 internet providers (Cable and DSL). I have never had to do anything to "spoof" something. The most drastic thing I have ever had to do are hard resets to the modem and/or router.

 

[serpretetsky]

Comcast has not done anything, you are confused. The cable modem itself learns the MAC of the first device it connects to, and only talks to that device UNTIL you power cycle it, then it forgets and looks for a new MAC. This is indeed the way ALL BRIDGE devices work. Cable, DSL, ISDN, etc. unless a router is embedded making it a gateway, its a bridge and that's how they work. If your not getting a private IP, it's a bridge.

This is strange. I'm not familiar on the whole process, but when the comcast installer came out to setup out internet at some point he told me he had to register the serial number on the modem I had before our internet would start working. I asked him if that was the MAC address specifically, and he said that, indeed, it was the mac address he was recording.

I'm not sure if he was lying or what. I also know the modem will be tied to the mac address of the first device it connects to, but this seemed like a separate thing all together.

You cannot spoof a cable mac address legally, it is burned into the eeprom chips. Comcast has no idea what the mac of his PC is and does not care what it is, people get new computers [and other internet devices Blu ray players, tv's, game consoles, etc...] all the time, that would be a costly headache to track. You can spoof the ROUTER's mac, but is not necessary, just power cycle the modem with nothing hooked up or even the router hooked up and it will LOOK for a NEW mac to talk to until it finds one.

Like someone else mentioned, many routers have the ability to spoof mac addresses built in. Plus many ethernet cards have the ability to change mac address.

I'm honestly not sure if it's actually ILLEGAL or not, but it's strange that everyone make it so easy to change the mac address if it is not legal. Can you point to the law that makes it illegal?

 

[Elixer]

Like someone else mentioned, many routers have the ability to spoof mac addresses built in. Plus many ethernet cards have the ability to change mac address.
...
I'm honestly not sure if it's actually ILLEGAL or not, but it's strange that everyone make it so easy to change the mac address if it is not legal. Can you point to the law that makes it illegal?

Routers yes, cable modems, no.
The ISP uses the MAC of the cable modem to 'know' who you are, so if people start changing that, then you could be on someone else's account and cause all sorts of issues.

 

[serpretetsky]

Routers yes, cable modems, no.
The ISP uses the MAC of the cable modem to 'know' who you are, so if people start changing that, then you could be on someone else's account and cause all sorts of issues.

ahh, gotcha, reread it again.

 

[Ichinisan]

Didn't read the thread, but I work for a cable ISP and I think I can shed some light on this. Most ISPs send a config file to the modem that sets the CPE limit to 1. It will only give a DHCP IP address to 1 device MAC. If the modem saw your computer first, the computer gets the IP. If you switch the connection to your router, the router will not get an IP until you reboot the modem (because the CPE limit has been reached).

A lot of people clone their PC MAC to the router and incorrectly think it's required. It's actually not required, but it does make things more convenient if you ever need to bypass your router while troubleshooting (you won't have to reboot the CM if your PC and router present the same MAC to the ISP).

The disadvantage of MAC cloning is that it can confuse someone at the ISP when they help you troubleshoot. The tech will see a MAC that's obviously not a router. When you tell them you have a router, they'll have to rule-out the likely possibility that the customer has incorrectly connected the CM to one of the LAN ports on the router.