Arris SB6141 and SB8200 DHCP issues

You need to power cycle the modem (8200) each and every time that you change the device that is being directly connected to it in order to obtain internet connectivity.

Thanks, EG. I've GENERALLY been doing that, though I'll admit it hasn't been EVERY time.

I've been looking for the critical sequence in powering-up/rebooting the router and modem.

I did manage to get one of my routers to get a DHCP-assigned address a few minutes ago., though it's not the one I was planning to use. I'll try repeating the process on the other three.

I'll update if I make any progress.

Thanks again,

Phil

Update:

This sometimes works. BUT: The link only stays up for about 45 minutes to an hour.

Changing routers doesn't change the fact that the connection is dropped after a short time. It's a little easier to tell when things fall down on the ASUS router. If it fails to connect, the network status says: Your ISP doesn't implement DHCP correctly. If it connects,  it gives me the WAN IP address. When it fails, it just says: disconnected.

I've been in touch with Xfinity tech support and so far they are little help.

The SB8200 modem has two ethernet ports. I was hoping I could plug into them both to check for any log messages when it disconnects, but plugging into one seems to disable the other.

Getting ready to call Arris tech support to see if there is any help they can offer.

More updates later.

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@BlueNGray wrote:

 

The SB8200 modem has two ethernet ports. I was hoping I could plug into them both to check for any log messages when it disconnects, but plugging into one seems to disable the other.

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FWIW, you would need to pay for an additional public / WAN IP address from them in order to use the second ethernet port. This feature is being phased out and is probably not even available anymore in your local market area. YMMV.

Not surprising.

I just got off the phone with Arris. They had me bypass the router and connect directly to the modem, which I did and am using that connection now. They wanted me to find out if this connection eventually drops out. I suspect it won't, but I'm not going to second guess it. If it does drop out, I'll call them back and they said they would probably replace the modem. But I don't really think that will help, since I was also seeing intermittent connection drops with my previous modem, an Arris SB6141.

Not sure it will work, but I'm thinking about putting a gigabit switch between the router and modem and see if I can bring up a computer running wireshark to monitor the traffic around the time it goes down.

For curiosty, What do the modem's signal stats look like ? Try getting them here; http://192.168.100.1

Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

Yeah, except I don't have one. After thinking about what I said last time, I realized it would not be as easy as it sounds. (In the absence of a port mirroring switch).

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@BlueNGray wrote:

 

Not sure it will work, but I'm thinking about putting a gigabit switch between the router and modem and see if I can bring up a computer running wireshark to monitor the traffic around the time it goes down.

 

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A *port mirroring switch* would work. You can Goggle for info.

Already confirmed with Arris that they are within limits:

Downstream levels: -8.6 to -2.9 dBmV

Downstream S/N: 

      data channels: 37.0 - 38.3 dB

      channel 37: 27.2 dB

Upstream levels: 45-47 dBmV

Looks like channel 37 is a bit low an shows some correctable/uncorrectable errors, but nothing that caused entries in the log.

I believe the mystery is solved.

I discovered that if I restore the internet connection without connecting my hardwired equipment plugged in (and leave them disconnected), the connection has stayed up overnight, which is far longer than it stayed up before.

Clearly, something I have pluggged in to the switch I have aggregating ports throughout the house is doing something that kills the connection between the router and the modem. I'm not sure whether the router or modem is what actually disconnects, but maybe I can determine that once I find out what device is causing the problem. I've got a suspicion I know what it is, but that's outside the scope of this thread.

Thanks for your comments and listening.

Quite welcome ! Good luck with it and please post back with how things turn out.

Network has been stable for several days.

I'm convinced the issue was related to some FreeBSD servers I have wire connected to the router. I also have a Linux Laptop and a TiVo Roamio and 2 TiVo Minis hardwired. When I disconnect the hardwire ports and reset the router (via a wireless link), the router connects to the internet. Then, when I connect everything (TiVos and Linux laptop) except the servers (which are shut down), things are still good. Then I fire up the FreeBSD servers and things are still ok.

I admittedly haven't tried very hard to reproduce the errors. That will have to wait until my wife isn't around. 😉 After being without her internet connection for almost a week, I'm reluctant to ask for trouble.  At any rate, it would seem that my original problem is self-inflicted, and outside the scope of Comcast/Xfinity tech support.

Yes.

I haven't seen an occurrence of the problem since I removed a defective RAM DIMM on my FreeBSD server. I thought I had reported this earlier.

Thanks for your reply, though.