Author Topic: Configure DPC3825 as pass-through device  (Read 7741 times)

tyriker

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Configure DPC3825 as pass-through device
« on: September 15, 2012, 10:29:27 PM »
Is it possible to have my cable modem/router configured to be a pass-through device, so that it does no routing and provides no network services and only behaves as a cable modem? I have a Cisco DPC3825.

I contacted customer support and made the request, but the person didn't understand what I was requesting. The best she did was simply disable the wireless on the DPC3825, and told me to just plug my own router into the DPC3825.

That is functional for getting on the internet, but isn't really what I want because I now have 2 routers on my network, with 2 firewalls, 2 dhcp servers, etc. I would prefer my Debian server to handle all of that stuff instead of the DPC3825.

Thanks.

MediacomJames

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Re: Configure DPC3825 as pass-through device
« Reply #1 on: September 15, 2012, 10:57:56 PM »
I believe what you are referring to is a "bridge mode" for the DPC3825.  Unfortunately those modems are not able to be put into that mode.  My recommendation for a situation like this would be to instead use a modem without the built in router capabilities.

tyriker

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Re: Configure DPC3825 as pass-through device
« Reply #2 on: September 15, 2012, 11:03:52 PM »
So I would need to go into the local Mediacom office and switch my current modem for another one? What modem (model) could I request that can operate in bridge mode. I'd also like it to support DOCSIS 3.0 as well.

MediacomJames

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Re: Configure DPC3825 as pass-through device
« Reply #3 on: September 15, 2012, 11:06:43 PM »
We do not have any modem/routers that can operate in bridge mode, however any stand alone modem will be able to do what you are looking for as they do not have a built in firewall or DHCP.  Unfortunately the modem models available, including DOCSIS 3 modems, will depend on stock at the local office.

tyriker

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Re: Configure DPC3825 as pass-through device
« Reply #4 on: September 15, 2012, 11:45:23 PM »
The DPC3825 does have the ability to run in bridge mode. Is this functionality just something that Mediacom doesn't enable?

The reason I wanted to switch to using my own router is because I've had connectivity issues with the DPC3825. I have a couple headless devices which drop from my network after a periods of inactivity. Rebooting those devices bring them back onto the wireless network. It's my belief that their wireless interfaces are going to sleep because the DPC3825 as an access point is not sending beacon frames frequently enough. However, I cannot see or change any such settings on the DPC3825 to verify or correct this. So essentially I wanted to use a router where I can see and control such settings.

So is there no option from Mediacom to get a cable modem without router functionality enabled?

MediacomDrew

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Re: Configure DPC3825 as pass-through device
« Reply #5 on: September 16, 2012, 07:12:25 AM »
The ability for bridge mode is dependent upon firmware and provisioning.  For residential tiers, bridge mode is hard coded as disabled within the unit's firmware.  A good swap for the DPC3825 so you can use your own modem would be a Cisco DPC3000.  This will offer the DOCSIS 3.0 capability that you are looking for, without the wireless gateway and built-in firewall getting in the way.  This is a stand-alone modem.  If you'd like, we can set up an appointment to have a tech swap this out for you.  Alternatively, this may be able to be swapped at the office.  I wouldn't be able to do this today- as it is Sunday- but we can check the availability of DOCSIS 3.0 modems tomorrow when they open.

tyriker

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Re: Configure DPC3825 as pass-through device
« Reply #6 on: September 16, 2012, 11:16:26 PM »
I won't be needing to swap out my modem. I found a way to do what I was trying to do.

MediacomJames

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Re: Configure DPC3825 as pass-through device
« Reply #7 on: September 16, 2012, 11:18:04 PM »
Great!  Let me know if there is anything else I can assist you with.

tyriker

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Re: Configure DPC3825 as pass-through device
« Reply #8 on: September 18, 2012, 01:30:51 PM »
For anyone interested, I did find a way to get my DPC3825 into bridge mode (to be a straight pass-through device, and not act as a router.) Most people will have no need or desire to do this, and if you're not comfortable managing and securing your own network, you should not do any of this. It is very likely customer support will not provide any help in this endeavor, and you may leave your home network vulnerable to attack. With that being said, proceed at your own risk.

First, you have to do a factory reset on the device (use a pen and depress the reset button for 10 seconds...the device will reboot). This will reset the device to CISCO's default firmware. You can find CISCO's manual for the device here: http://www.cisco.com/web/consumer/support/userguides2/4021196_B.pdf , as it describes the non-Mediacom admin screens of the device. The IP Address will be reset to 192.168.0.1. If you connect directly to the device, you should be able to browse to the IP Address to bring up the admin. If you want to connect wirelessly, the SSID was reset to the last 6 characters of the devices MAC Address, and the PSK is the S/N value of the device. You can find this information on the sticker on the bottom of the physical device.

Second, you need to use the CISCO admin screens to put the device into bridge mode (instead of "Router Mode"). However, the UI to achieve this doesn't actually exist in CISCO's admin screens. But you can still [HTTP] POST the proper data to the device and put it into bridge mode. See http://ohmsblog.teamohms.org/2012/06/how-to-switch-cisco-dpc3825-epc3825.html for more info.

Essentially, you need to go to the "Administration" screen and the "Management" tab. The <form> element on this page can accept a value for "working_mode". A value of 0 is for router mode, and a value of 1 is for bridge mode. All you have to do is POST this value to this form and the device will accept it. You'll know it worked because you'll get a rebooting... screen after submitting the value.

You can submit/post this value to the form in any number of ways. The simple way I did it was by using the Dev Tools within the Google Chrome browser. Open the dev tools, drill down into the <form> element, edit the HTML and simply add an <input> tag with the proper name and value. Then within the page click the "Save Settings" button. This will submit/post your inserted name/value to the form.

After rebooting to bridge mode, you're on your own as to what you do next. But here's some things to know:

 * If you are hard-wired to the DCP3825 (ethernet), your computer is now publicly exposed to the internet. This is dangerous if you are not properly protected.
 * The DCP3825 does not automatically turn off the wireless side when in bridge mode. I didn't experiment much here as I simply disabled the wireless after switching to bridge mode.
 * The IP Address of the device switches to 192.168.100.1 when in bridge mode (wireless side only). I believe much of the network services (DHCP, etc.) are turned off when router functionality is disabled. If you connect to the device wirelessly, you may need to give yourself a static IP Address in the 192.168.100.0/24 range in order to communicate with it.

One nice [potential] side effect of me doing this is my connection is measurably faster. Before, I consistently tested at 9 Mbps on http://speedtest.net/ . After switching to bridge mode and using my own router, firewall, etc. I regularly test at 27 Mbps. However, there are many variables at play here, and just switching the DCP3825 to bridge mode may not be the reason behind this apparent increase in network speed.

MediacomDallas

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Re: Configure DPC3825 as pass-through device
« Reply #9 on: September 18, 2012, 02:03:49 PM »
That is not a method we officially support though but I'm glad it got the job done for you.