How do I use custom DNS settings on the CGN3ACSMR modem?

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I Plan to Stick Around
Posts: 12

Re: How do I use custom DNS settings on the CGN3ACSMR modem?

I've attached any relevant screenshots from the CGN3 and the network status on the tablet.


Screen Shot 2018-06-20 at 12.57.08 PM.pngScreen Shot 2018-06-20 at 1.18.19 PM.pngScreen Shot 2018-06-20 at 1.18.51 PM.pngScreen Shot 2018-06-20 at 1.19.06 PM.pngScreen Shot 2018-06-20 at 1.19.51 PM.pngScreen Shot 2018-06-20 at 1.23.35 PM.png

I Plan to Stick Around
Posts: 12

Re: How do I use custom DNS settings on the CGN3ACSMR modem?

And attached here is the network status on the tablet after I specify the DNS settings manually on the tablet (and it works).


Screen Shot 2018-06-20 at 1.29.42 PM.png

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Posts: 5,500

Re: How do I use custom DNS settings on the CGN3ACSMR modem?

Edit:  ok, the images are visible now.  I should have asked earlier, can you confirm the Software (firmware) loaded as seen in the STATUS page when you log into the modem.  Looking at the image, its hard to determine exactly what it is, but it looks like 4.2.x.15??  The latest version available is (April 13, 2018).  That might be a trial version.  There is nothing in the release notes that indicates any addition of a VPN feature, but, its definitely there.


Fwiw, the addition of a VPN feature is rather interesting.  The Intel Puma 6 and 7 modems have a long disappointing history when it comes to IPSEC and VPN operation.  VPNs either don't work, or they work at low data rates, nowhere near the non-VPN data rates.  Understandably there are issues of processor horsepower and data rates, but, until now, the VPN client would run in the router or connected device.  All the modem has to do is transfer the data to the CMTS, and as seen over the previous years, its done a poor job at that.  So, how well any VPN will run on the CGN3ACSMR is a rather interesting question.  I think that you're going to be the willing or unwilling volunteer for this exercise.  

I Plan to Stick Around
Posts: 12

Re: How do I use custom DNS settings on the CGN3ACSMR modem?

Thanks.  The firmware version I currently have on the CGN3 is - I had already read the last page of the link you posted and while the latest firmware on the CGN3ACSMR is, I have the CGN3 and it says the following:


Hitron CGN3

Model: CGN3ROG
Current production firmware:
Current trial firmware: TBD
So I do believe I have the latest firmware.
If I can get the DNS/VPN running, I am more than happy to play around and post the results here!
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Posts: 5,500

Re: How do I use custom DNS settings on the CGN3ACSMR modem?

Ah, ok, now this is starting to make more sense.  Looks like the VPN addition wasn't posted in the firmware release list and no one, until now, has brought up the issue.  


Fwiw, the CGN3 was the first Intel Puma 6 modem introduced by Rogers.  That modem, and all of the follow-on CGN3xxxx modems have or had issues with latency to and thru the modem.  That is the result of design decisions made by Intel after they bought the Puma modem line from Texas Instruments in 2010 (?) and took a swing at making a consumer modem.  The result was a modem comprised of two processors, one of which is an Atom processor, while the other is an ARM processor as seen here:


Also included in the modem's chipset is a MaxLinear tuner to support 24 or 32 channel operation, depending on the chosen tuner chipset.   The problem is the lack of horsepower in the modem's chipset and some unknown task that runs every 1.92 seconds or so.  That causes the modem to buffer any incoming and outgoing data which results in a latency spike when that data is finally processed.  Rogers started working on the problem in June 2016 following my complaints about the CGNM-3552 modem which was brand new at the time.  By Sept 2016 Intel had issued an update that fixed the IPV4 ICMP latency thru the modem.  The question from then was, what about all of the other protocols and IPV6 protocols as well.  There have been updates for the CGN3ACSMR and CGNM-3552 modems which probably partially resolve some of the latency for the other protocols.  Some of those updates have probably trickled down to the other CGN3xxxx modems but I don't know exactly what has or hasn't been changed in the other modems and now that I'm running the Puma 7 CODA-4582, I'll most likely never see an opportunity to test the CGN3 series modems to determine if Intel's firmware updates have been successful or not.  The Puma 7 modem doesn't suffer from the latency seen in the Puma 6 modems, but, the issue with IPSEC and VPNs is still present.  


So, the upshot of all of this would most likely be that the CGN3 still has not been fixed and as a result, any game or latency intolerant application that you run will be affected by the latency thru the modem.  Here's a shot of the CGNM-3552 modem, running a ping test to the Cable Modem Termination System which the modem connects to.  This was done with Pingplotter, running one ping every 2.5 seconds.  If the ping rate was increased, you would see a great many more latency spikes.


So, this is out to the CMTS and back again, one hop out and back.  Notice the latency spikes ranging up into the 200 milli-second range.  That is what I suspect you would see with the CGN3.  If you ran a trace to anywhere, google for example, then used the second hop IP address as a ping target, you should see occasional ping spikes in the data if you just let the ping test run:


ping -t


Use control^C to bail out of the test.  You should be able to just read thru the return times to see the high values.  


Ok, so, the changes to the firmware were made to hand the processing off to the hardware processor / accelerator instead of handling the processing via CPU based software process.  That produced very good results for IPV4 ICMP processing.  Only question is, what happened with all of the other protocols.  To date, no one has really been able to test the modem with the latest firmware loaded.  That's a combination of newer firmware being unavailable at some ISPs and the lack of experience necessary to really test the modems.   Customers with Virgin Media in the UK are just now receiving the latest version firmware for their Puma 6 modems.


The CPU looks at every packet in order to determine what to do with it.  There is one exception, at least for the CGN3ACSMR / CGNM-3552 modems, and that is the VPNs.  When the VPN tunnel is established, its handed off to the hardware accelerator / processor and the CPU doesn't bother with it, so, it just runs.  That has allowed users to run video streaming with some success, at least better than without the VPN.  So, although the VPN can work, there are other factors at play that we haven't determined.  Those factors result in much less than optimal results for VPN operation.  All of the CGN3xxxx modems are similar but not exactly the same, so, they don't all run a unified firmware version.  When that eventually happens, if it happens, it will make the task of arriving at solution for the latency problems much easier. 


The CGN3 itself appears to be on its own at the present time.  I don't know if the changes to resolve the latency issue will ever percolate down to that modem, so, be aware that you might be seeing latency to and thru the modem and there is a good reason why.  I don't believe that the VPN addition has made an appearance in any of the firmware versions for the CGN3xxxxx modems, but hey, I could be wrong as no one has brought up the issue.  


The Puma 6 modems have been a problem worldwide, and will continue to be a problem for a few years to come as many ISPs in the U.S. don't update customer owned modems.  So, this problem will drag on for a few years.  


Last but not least, the Puma series modem all have a DOS vulnerability, in that its possible to bring the modem to a halt with a low rate targeted attack.  Thats yet another issue that Intel has had to deal with in the midst of resolving the latency problems.  Have they managed to solve it?  Don't know.  Can they really solve it, considering the hardware and firmware architecture?  Also don't know.  Guess we'll start to see fairly soon.  


Here's a link to the second of two threads concerning the Puma 6 modems.


Hopefully all of this sets the scene for the experiments that you're about to undertake.  I hope this works, but, I won't be surprised if it doesn't.  What is it they say in the movies "Your mission, should you choose to accept it .......... "



I Plan to Stick Around
Posts: 12

Re: How do I use custom DNS settings on the CGN3ACSMR modem?

Wow - thank you VERY much for taking the time to share your knowledge in so much detail - you really know your stuff!  Sounds like the CGN3 is both a hardware and a firmware nightmare, so it looks like I'll be configuring it in gateway mode and connecting my own router.  I appreciate all your help!

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