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[Gatorbait]

I can't seem to get DIR-655 to communicate with Motorola SB6121 cable modem.  Don't know if it has anything to do with the old firmware 1.21??  Should I update the firmware?  If so, which version?
Any help is appreciated.  Thanks in advance.

[Hard Harry]

1. ISP?
2. Static IP or DHCP from ISP?
3. Is the ethernet from modem going into Internet port?
4. Have you tried a full sequenced power cycle? (Turn everything off, turn on modem, wait to sync, turn on router, wait to sync, turn on PC)

[FurryNutz]

Check the cable between the Modem and router, sometimes those cables made well. Cat 6 recommended.

[Cobra]

Don't forget to powercycle the modem.

[Gatorbait]

1. ISP?
2. Static IP or DHCP from ISP?
3. Is the ethernet from modem going into Internet port?
4. Have you tried a full sequenced power cycle? (Turn everything off, turn on modem, wait to sync, turn on router, wait to sync, turn on PC)

1.  Comcast
2.  DHCP
3.  Yes
4.  Yes

[Gatorbait]

Check the cable between the Modem and router, sometimes those cables made well. Cat 6 recommended.

I was using a cable modem provided by Comcast (Motorola SB 5120) without any problems.  After swapping out the cable modem to the SB6121, I was able to get on the internet with the computer connected directly to the cable modem but when I connected through the router to the cable modem, I could not connect to the internet.  I am now back on the SB5120 and connecting without any problems through the router.  I am assuming that the cables are ok.

[FurryNutz]

My 655 was connected Friday to my 6121 with out issues. Didn't have to power cycle the modem however in your case you might need to. Power everything off, then power up the modem and let it sync. Then power on the 655. Look at the status section on the routers web page. You can see the WAN connection info there.

Is the router set for automatic Speed on the WAN port? You can try using Manual. I Think I set mine for Gb.
Might swap cables to test. I recommend CAT6 and shortest length possible between Modem and router.

[alien]

look out you need at minimum 1,5 meter of cat 5e or 6  kabel otherwhise it wont work.
look into the router if it gets an ip from comcast.

[FurryNutz]

Meter works out to be in inches 4.9 feet of CABLE which isn't required. 1 Foot works get if you can use that.

[Hard Harry]

1. How long is the cable between modem and router?
2. Do you have a normal Comcast account or Comcast Buisness?
3. Have you tried a factory reset? Maybe you had MAC cloning on the router and that is doing something? Or maybe you have the DHCP IP set on the WAN as a Static IP?  Unlikly, but trying to think outside the box.
4. With the 6121 connected to router, what does the status say? And is the link light on the 6121 on or blinking? Trying to see if it's atleast detecting the physical wire.

Really a SB5120 and SB6121 should be almost identical(as far as this problem is concerned). The only thing different I can see that is relevant is the 5120 has a 10/100 port while the 6121 has a 10/100/1000 port, so maybe there is some duplex issue.

[FurryNutz]

Motorola roll out a new modem Harry? 6180? 

[Hard Harry]

Woops. I was just researching the SB6580 on another forum so the 80 was stuck in my head. Edited.

[WiredCaveMan]

I have the same issue. I switched from DSL to Comcast cable a couple of weeks ago. I researched the approved Comcast modems and opted for the SB6121. The installation was completed with the new cable modem while it was connected to the PC directly. After the tech left, I tried to hook the cable modem up to the router, to no avail. All of the lights on the modem were on normally, except for the “Link” LED, which gave me a blink or two and that was it.

My setup:

• Motorola SB6121 connected via coax
• DIR-655 revision A
• Two pieces of patch cable tested at 1 GB
• The cable modem is connected via coax with one patch cable to the WAN port and from the router to the pc with the other patch cable.

I have tried the following configurations, settings, and firmware with router reboots between all setting changes with negative results for every try:

• I began with firmware version 1.21 (11/07/2008).
• I hooked up the router, which was already set up to receive DHCP from my last provider.
• I reset the router, wiping out all settings, and set the router up using the “Internet Connection Setup wizard” with “Comcast” as the ISP (DHCP), while cloning my PC MAC address.
• I tried setting the WAN connection to 10 / 100 / 100 (automatic) and tried the manual setting at 1000, which is what the SB6121 is supposed to be set at.
• I tried using PPPoE with my username and password for Comcast (which is the wrong setting, but I tried anyway).
• I disabled Unicasting.
• I disabled the Router firewall.
• I disabled the Advanced Domain Name System.
• I disabled the QoS engine.
• I allowed multicast streams.
• I upgraded the firmware to 1.35NA (12/28/2010)
• I rinsed and repeated everything above with the new firmware (except for my original DSL settings, which I had wiped out).

After all of my attempts, I reset the router to factory defaults and called Comcast. Comcast took me through the basics of restarting the modem, restarting the router, checking connections, and making sure that the connection was set up in the router for DHCP. Host names and DNS ip addresses were not required. Nothing worked.

My next call was to Motorola. The first line tech took me through about the same process as the Comcast tech. Nothing worked, so he set me up with a second tier Motorola tech.

A couple days later the second tier guy called. We went through most of the same simple things such as making sure all of the lines were secure, making sure that the router was set to DHCP, making sure that the internet connection was working with the PC. We did several reboots of devices, etc. Finally, the tech came to the conclusion that I might have a bad WAN port on the router, which did make sense, since the cable modem connected to the PC just fine and we got the nice “Link” light with the pc, but not with the router.

I took the router to work the next day, hooked up the WAN port to the network and hooked up one of the LAN ports to my PC and everything worked right away.

Unless anyone can figure out what I might have done wrong, I have come to the conclusion that my new Motorola SB6121 and my D-Link DIR-655 just won’t talk to each other. It just seems really weird. If anyone can give any input, it would be greatly appreciated.

[davevt31]

Did you power cycle the modem when changing from connceted to the PC and connecting to the router?  A power cycle is necessary so that the modem picks up the MAC address of the newly connected item and passes it an IP address fromyour ISP.

[FurryNutz]

Well I got my Rev B connected with out any issues to my SB6121 last week.

After powering up the Modem and letting it sync, then powering up the 655 you still can't get any internet?
Whats the status say under Status/Device Info/Wan section?
You should need any PC Mac cloning. Turn that off.