Motorola SB5101 modem drops WRT54GL router

Discussion in 'Tomato Firmware' started by Starfury, Apr 16, 2009.

  1. Starfury

    Starfury Addicted to LI Member

    I finally got around to installing Tomato on my WRT54GL yesterday. Unfortunately, now the router doesn't seem to want to stay connected to my Motorola SB5101 cable modem. I cleared the nvram after flashing the router, rebooted the router and the modem, and verified the router was getting an IP from the modem (actually, from the ISP, as the modem is apparently set to run in bridge mode as soon as it's connected to the ISP). As soon as I try to access anything outside my LAN, the connection from the router to the outside world drops. I can't get the IP to renew without rebooting the modem.

    I've tried a couple other firmware types without any similar problems, and the original firmware works as well. The only time I have this problem is with Tomato. I'm currently running Gargoyle, but I would like to go back to Tomato if I can get it to work properly.

  2. WRobertE

    WRobertE Addicted to LI Member

    No Problems With That Configuration Here

    I've been using a SB5101 with a WRT54GL running Tomato for quite a while without any disconnect problems. So, there's not a hardware incompatibility.

    Maybe try downloading a fresh copy of Tomato, reflashing and doing the thorough NVRAM erase again. Sounds like the Tomato install got corrupted.
  3. Starfury

    Starfury Addicted to LI Member

    Hmm...I'll try that and report back.
  4. Starfury

    Starfury Addicted to LI Member

    No dice. Downloaded a fresh copy, installed from a .trx file this time instead of the .bin, still won't stay connected to the modem/ISP after I try to access anything outside. Tried checking the 'reduce packet size' option, still nothing.

    Any other ideas?
  5. gawd0wns

    gawd0wns Network Guru Member

    Login into your router and look read through the logs. You should be able to access it by going to
  6. WRobertE

    WRobertE Addicted to LI Member

    I think he means log into the MODEM. The address given is the default address for the SB5101. But, it's a good idea. Maybe the logs have some useful information in this case.

    Here are some other things I'd try:

    1) In Tomato, go to Status, Logs and see if there are any messages that may point to a cause.

    2) I would reset the cable modem. After logging into the Modem at the address, click on the "Configuration" tab on the left, then click on "Restore Factory Defaults", then click on "Restart Cable Modem". It may take 5-30 minutes before your modem is re-detected by the cable system and the configuration information is downloaded into the modem.

    3) check the tcp/ip settings on the computer and veryify that you using "Obtain IP Address Automatically" and "Obtain DNS server address automatically". (see first attached image)

    4) on the screen referenced in step 3, click on the advance button and make sure the screen looks like the 2nd attached graphic.

    I know you said it worked fine with other firmware, but sometimes it's necessary to start from the beginning and work thru it step by step to find the problem.

    Attached Files:

  7. callous

    callous Network Guru Member

    Long shot, but why dont u try forcing the WAN Port Speed to something else other than Auto.

    This assumes your router loses connection to the modem.
  8. FattysGoneWild

    FattysGoneWild LI Guru Member

  9. Starfury

    Starfury Addicted to LI Member

    Not an issue with my computer getting an IP, as the LAN always seems to work (although my TCP/IP config is set obtain DNS and IP automatically). The modem simply does not like Tomato. For clarification, I'll sit and stare at the Tomato connection status screen (3sec refresh) while the modem boots. Once it gets an IP, I'll try to browse somewhere, or run a command line ping. As soon as I do that, the status screen shows that the router loses its IP and refuses to renew until I reset the modem.

    I don't have time to set it back up and check the logs right now, but I'll post what little there is when I get time. I don't recall seeing anything that flagged my attention in the router logs, just some timeouts. Didn't look at the modem logs.

    I tried manually setting the port speed to 1492 and it didn't make any difference. Didn't try anything lower, but the default 1500 seems to work for other builds.

    Haven't reset the modem to factory specs...but don't understand why that would make a difference if every other build I've tried seems to work fine. I'll give it a shot, though.

    Currently I'm running dd-WRT, which seems to be stable and has most of the options Tomato does, but is still missing some things I liked, especially in the QoS area. I'll try to find some time to play with it in the next few days and report back.
  10. WRobertE

    WRobertE Addicted to LI Member

    By the way, 1492 and 1500 are not port speed settings. Instead, those numbers refer to something called MTU (Maximum Transmission Unit). Since you are using a cable modem, this should be left as the default of 1500. The 1492 value is used by DSL configurations.

    Go here for more on this setting:

    As for resetting the modem, the reason I recommended that is because the modem "remembers" the MAC addresses of the devices connected to it. This can be seen in the modem's "Addresses" status screen. By resetting the modem with the router attached, the modem should see the router and "remember" the router's MAC address. You didn't mention what ISP you're using, but maybe they have some restriction on the number of devices they think are attached to the modem. So, if the modem has already "remembered" a device, maybe it won't talk to another one that's now directly connected.

    This also relates to a prior reply related to MAC address cloning. If the DD-WRT or other firmware had "cloned" your PC address already, then in those configurations the cable modem "sees" the router with those firmware as the PC since all the modem sees is the MAC address of the device that's directly connected to it. If you haven't done this in Tomato, the modem now sees a different MAC address and it may be interacting differently. So, as mentioned in a prior reply, you may want to try "MAC Address Cloning" in Tomato and see what happens.

    In Tomato, go to "Advanced" then "MAC Address" via the navigation menu on the left. In the WAN Port area, click "Clone PC" and the WAN Port MAC Address of the router will be replaced with the MAC Address of the PC. You MUST scroll down and click "SAVE" for the change to take effect. As a precaution, I'd write down the current MAC address values before clicking on "Clone PC" in the event you have to change it back.

    It's a long shot, but it's one possibility.
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