Equipment (Modems,Gateways)
Modems, Gateways, and Networking Devices
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DPC3939B - Reserved IP Conflicts

I've been using the DPC3939B through three changes of computers.  Two of the computers are using completely new NICs, and as such have different MAC addresses.

 

For some reason, the DPC3939B fails to recognize that the old machines have been taken online.  They still reside under the "disconnected devices" section of the "Connected Devices" section of the management interface.

 

This causes a huge problem.  The computers in question have the same name, and the old one no longer exists for me to be able to change the setting back to DHCP for the given device, so I can give my current machine the same IP address the old one used to have (10.1.10.100).  The IP address being 10.1.10.100 is actually quite important, considering the fact that the rest of the network depends on the IP being that one, and not any other.  Hence my dilemma.

 

I cannot, for the life of me, get the router to forget the old IP assignment of the OLD device.  I've tried deleting it, and it never gets deleted.  It goes from being blocked, to being unblocked and back in the "disconnected devices" listing.  Either this modem has some severe issues from a firmware standpoint, or there is just a major lack of PROPER, REQUIRED management options for it.

 

I need a way of removing and reassigning these disconnected devices, so I can reassign the IP addresses they were originally designated to have.  The new machines must take their place on the network, and the way things are now makes it impossible.

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Re: DPC3939B - Reserved IP Conflicts

I don't have experience with how the DPC3939B handles DHCP devices, but as a workaround, you could just assign the 10.1.10.100 device with a static IP, then set the DHCP range on the DPC3939B to exclude 10.1.10.100.

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Re: DPC3939B - Reserved IP Conflicts

Hello Khanduras and welcome,

 

One alternative to remove any device from the DPC is to use the MAC filter facility which I believe is located in the Manage Devices Element. This should remove any devices from the device disconnect list and will auto-reconnect to the connected device list for you. 

 

Could you share any information wrt the speciality of the 10.1.10.100 device and are you using this address outside of the DHCP Service dynamic IP range?

 

Look forward to hearing from you.

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Re: DPC3939B - Reserved IP Conflicts

I tried using the MAC filter ability to remove the MAC address of the old computer which previously took the 1.10.1.100 IP address only to find out that it doesn't actually remove it - just blocks the machine's MAC address from connecting to the router, rather than actually remove the recognition of the device.  This still leaves the IP address unable to be used.

 

I had to reset the device back to factory settings to get it to forget the IP address, and thus experienced way too much downtime because of it.

 

In-house, the 1.10.1.100 IP address was used as a dedicated DNS server for a number of internal machines.  Most of the network expects it to be there, and switching the IP address around would have resulted in the same amount of downtime, if not more, as setting the thing to factory default settings would have.

 

Unless someone knows about something I may be missing, this modem/router combo seems to be ill-suited for practical applications.  Maybe for small business owners who don't know what they're doing, but for those of us who typically do know what we're doing, it's a pain in the ass.  Should probably just put it into bridge mode and put some proper hardware behind it.

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Re: DPC3939B - Reserved IP Conflicts

Same issue here, I can't find any way other than a factory reset to clear the reserved IPs if you can't connect the original device. In my case, I picked the wrong MAC for a device with multiple, so the only way I am ever going to connect that MAC is if I spoof it.

 

Does a factory reset restore the password given by the Comcast tech during install or some other password?  I have been hesitant to do that because I didn't know where it would leave me.

 

I have the original password given to me, but "factory" may mean that the password is something else that I don't have.

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Re: DPC3939B - Reserved IP Conflicts

I just restored my gateway back to factory settings today.  Partly for the same reason in this discussion.  The password went back to highspeed

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Re: DPC3939B - Reserved IP Conflicts

This was the only way I was able to reset the DHCP addresses as well.  But BEWARE if you have static IPs, this erases them all and you have to get support to put them back for you.

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