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DPC3941T Bridge Mode - LAN To Router Completely Drops

New Poster

DPC3941T Bridge Mode - LAN To Router Completely Drops

I recently moved and was upgrade to the DPC3941T modem. Because I already had a good home network, I am using it in Bridge Mode to a Netgear WNDR4500v2. Everything is working great, I'm getting the speeds I expect, everything's fine.

 

Except, randomly, maybe once every few days, or today, twice in one day, the connection is cut.

 

By this, I mean that the Internet light on my Netgear router is completely out. The Xfinity modem is still on and has the wifi signals blinking on the front (even though I've disabled them) but there are no lights on the port on the back (yes, I'm using #1). I can hotswap out the cable and it does nothing.

 

A reboot of the Xfinity modem fixes this. No need to reboot ther router.

 

I have swapped ethernet cables between the modem and the router three times. I have also tried other ports on the modem, even though I know #1 is the port you're supposed to use in Bridge Mode.

 

I have not attempted to take the Xfinity modem out of Bridge Mode because I don't want a double NAT situation.

 

Is this a firmware issue or should I try to swap the modem out at a store?

 

Once again, I don't believe my connection between the modem to the Xfinity Network is cut, it's just the connection between LAN #1 on the back of the Xfinity Modem to the Internet port on my Netgear router. When it's working I'm getting the speeds I expect.

 

Thanks for your time.


Accepted Solutions
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Figured I'd post a followup after several weeks for the sake of any Google searches.

 

Swapping out the modem was the solution. I have had no issues with the LAN ports freezing up with the new model since I got it almost a month ago.

 

While this thread was mostly about signal strength, the signal strengh had absolutely nothing to do with the faulty ports on the back of the modem, and was a wild goose chase that I could have done without. It's a typical case of ignoring the actual problem and instead investigating what is "easy" and something that might even involve paying money to Xfinity to have a tech deal with. The actual solution took me just a few minutes - take modem to Xfinity store, swap it out, reconfigure it. No visit needed, no new cables (even though the cables were just run initially a few weeks before), no tech visit, and no money.

 

Lesson: Not everything is tied to signal strength.


All Replies
Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Have you tried rebooting your router and looking for any firmware updates for your router?
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Rebooting the router was the first thing I did the first time this happened. Curiously, the internet light did not come back on (nor did the port reactivate) until I rebooted the modem. I can fix the issue solely by rebooting the modem without rebooting anything else.

 

I did just recently upgrade the router's firmware. It's current now but it wasn't too far behind.

Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Ok. I know you do say that you believe their isn’t an issue with signals but I would say let’s look at them anyhow just to make sure. I believe since it is in bridge mode that it should http://192.168.100.1
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Actually still at 10.0.0.1 for whatever reason. (Yes, it does state it's in bridge mode and does act like it is in bridge mode.)

 

Using an image because it seems cleaner to me than cut/paste.

 

XfinitySignals.jpg

Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

May I see the rest of the downstream channels? So far one looks a bit low and all of your upstreams are out of spec / too high.
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

I totally missed the scrollbar. I feel dumb.

 

Copy/pasting because there's a lot:

 

 

Downstream
Channel Bonding Value
Index
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Lock Status
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Locked
Frequency
657 MHz
513 MHz
519 MHz
525 MHz
531 MHz
537 MHz
543 MHz
555 MHz
561 MHz
567 MHz
573 MHz
579 MHz
585 MHz
591 MHz
597 MHz
603 MHz
609 MHz
615 MHz
621 MHz
627 MHz
633 MHz
639 MHz
645 MHz
651 MHz
SNR
40.366 dB
40.946 dB
40.946 dB
40.946 dB
40.946 dB
40.366 dB
40.366 dB
40.366 dB
40.366 dB
40.946 dB
40.366 dB
40.946 dB
40.366 dB
40.946 dB
40.366 dB
40.366 dB
40.946 dB
40.366 dB
40.366 dB
40.946 dB
40.946 dB
40.366 dB
38.983 dB
40.366 dB
Power Level
-7.300 dBmV
-5.000 dBmV
-5.000 dBmV
-5.000 dBmV
-5.200 dBmV
-4.900 dBmV
-4.900 dBmV
-5.000 dBmV
-4.900 dBmV
-5.000 dBmV
-5.000 dBmV
-4.800 dBmV
-5.200 dBmV
-5.200 dBmV
-5.300 dBmV
-5.300 dBmV
-5.500 dBmV
-5.800 dBmV
-5.900 dBmV
-6.100 dBmV
-6.500 dBmV
-6.500 dBmV
-7.000 dBmV
-7.100 dBmV
Modulation
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
256 QAM
Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

No worries it’s actually common to miss it. Believe me. I used to not notice it. Ok. Do you have any splitters that can be removed because of them being unnecessary? Also, I would check the wires by unplugging them and check for corrosion and remove the corrosion if any or any possible water damage. Also if you have any filters that are designed to reduce the signal, I believe they are called attenuators, even though I just call them reducers myself to make it simple for myself, I would remove them. I would also try replacing some splitters if any leading up to the gateway with newer bidirectional 5-1002 MHz rated. You don’t need gold colored trash splitters from stores like Target and all of them. The following steps are self efforts to try to raise the downstream levels and lower the upstream and I would say after that if you still can’t get those signals good then I would say it may be time after that to have a technician investigate however if the problem is within your lines and the tech finds it in your lines and you don’t pay for the $6 protection plan you will be charged for the visit but if the problem is a faulty device from Comcast or the problem is beyond your premises you won’t be charged.
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

This house was just wired by a Comcast tech a few weeks ago, so I'm pretty sure everything in it is necessary and relatively new wire wise. (They did re-use some existing cabling in the walls, though.)

 

If the connection between the modem and router goes dark again I'll consider having them out, but all of the lights on the front of the modem say that the downstream/upstream is just fine.

Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

The lights won’t all the time indicate a problem being present. The signals aren’t great but their not bad enough to prevent channels from locking at the moment. I would ask for the event logs for you but they’re likely to be blank which is the gateway’s fault but anyhow hope all goes fine if you need a tech visit. Keep us updated. Also, the reason why Wi-Fi light are still on is probably because xfinitywifi may be broadcasting from your gateway. Some are thinking it might just be in he firmware itself but anyhow as long as the gateway says it’s in bridge mode and as long as your router isn’t getting a 10.0.0.X address then you know the router side is disabled.
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

I have the xfinitywifi hotspot disabled through my account on the site, and I don't see it in my list of wifi networks, so who knows. None of the logs on the modem exist when I try to look at them, but I'm locked out of the advanced stuff since this is a leased modem.

 

Thanks for digging into it. I appreciate it.

Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

No problem. I used to have one then didn’t like the way the 3941 were operating at all anymore with blank logs along with a few other issues then swapped for a 1682 and had only one minor problem since. Just to add something, did you try a factory reset of the 3941 by holding in the reset button for 30 seconds and then re-enabling bridge mode and then connect the router and power it up? Just trying to help to save you a tech visit if possible even though you might need one anyhow.
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

So to give an update, it dropped twice this morning while I was on a videoconference with a client so when that meeting was over, I finally decided to factory reset, which made everything worse.

 

When the modem gets in this state, both lights on each Ethernet port were solid on, even if there was nothing plugged into it. When I factory reset the modem, it immediately went into that state, so the only way I could get into it was over Wifi. Using Wifi, I was able to reconfigure it, but I couldn't connect anything hardwired to the router. I turned it into bridge mode, and got a wired connection for about a minute before the ports all went back into that state.

 

I called tech support and she was able to verify that yes, my modem was connected to their network and bridge mode was enabled, so it has nothing to do with the signals. I just exchanged the modem out at the store (luckily it's only 5 miles away) and just got it set back up in bridge mode. They swapped out for the same model.

 

We'll see if it stays this way!

Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

We’ll hope the issue is fixed but if not it is a signal problem because replacing equipment typically does not change the fact that your upstreams are high and downstreams are a bit low. You can still have signal problems and the modem can still be online to them, all it needs are the channels to lockup no matter how they are. Let’s see how this holds up. Do you happen to know if they gave you a completely different model or is it the same model?
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Exact same model. The signals are the same, but after seeing what happened when I factory reset, I think the LAN ports on the model were just bad, since they started doing the both-lights-always-on thing before the modem even tried to connect to the Xfinity network, but I could still get online via the wifi just fine (when not in bridge mode.)

Problem Solver

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Ok. Just wanted to make sure that you did put it back into bridge mode? You might want to make sure the shut xfinitywifi off on the new one in case if you don’t want it. Sometimes that setting doesn’t transition when putting a new one on.
New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Figured I'd post a followup after several weeks for the sake of any Google searches.

 

Swapping out the modem was the solution. I have had no issues with the LAN ports freezing up with the new model since I got it almost a month ago.

 

While this thread was mostly about signal strength, the signal strengh had absolutely nothing to do with the faulty ports on the back of the modem, and was a wild goose chase that I could have done without. It's a typical case of ignoring the actual problem and instead investigating what is "easy" and something that might even involve paying money to Xfinity to have a tech deal with. The actual solution took me just a few minutes - take modem to Xfinity store, swap it out, reconfigure it. No visit needed, no new cables (even though the cables were just run initially a few weeks before), no tech visit, and no money.

 

Lesson: Not everything is tied to signal strength.

New Poster

Re: DPC3941T Bridge Mode - LAN To Router Completely Drops

Instead of turning on Bridge Modem, there's another way to disable the WiFi, that solved connection problems to my router.

Step 1. Go to Gateway > Connection > WiFi > under the "Private WiFi Network" click the "Edit" link.

Xfinity Gateway - setting to disable WiFi - step 1.png

             That takes you to "Gateway > Connection > WiFi > Edit 2.4 GHz" pane.

Step 2. Click the "Disable" button to turn off WiFi.

RESULT: For me it disabled WiFi just like bridging the modem without the errant behaviors.

Xfinity Gateway - setting to disable WiFi - step 2.png