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Losing IP address from cable modem in bridge mode every two weeks

Frequent Visitor

Losing IP address from cable modem in bridge mode every two weeks

Hi,

I have an ARRIS TG1682G (10.1.7.SIP.PC20.CT) Gateway/modem in Bridge Mode. I have a new Netgear 7000P that is connected to that gateway. When I installed it about 6 weeks ago, it would not get, or the gateway would not give, an IP address. I called Netgear support and they had me direct connect a PC to the gateway, then during the router setup, I needed to use the PC MAC address (IP spoof?) to get things working. Strange, but it worked.

About two weeks later, I lost internet access and find that the router does not have a working IP address again. I went through the same procedure and got it to work. I crossed my fingers to hope the fix would be permanant. Unfortuantley, two weeks later, I got the same problem and solved it with the same procedure.

I have also talked to Comcast support and they don't have an answer as to why this is happening and call the problem solved when we get things working again with the procedure described above.

My guess is that Comcast makes you get a new IP every two weeks and that cause the problem, but that is a guess. I posted this same message in the Netgear forums and on the Comcast subreddit. Is there some way to fix this so I don't have this problem every other Friday morning?

Thanks.

Frequent Visitor

Re: Losing IP address from cable modem in bridge mode every two weeks

UPDATE:  It has been an interesting couple of days.  Yesteday, the router lost it's IP address again, 0.0.0.0.  I had been monitoring the DHCP Lease Time and Renewals.  The Lease Time is usually 4 days and it gets renewed before 2 days have elapsed.  The renewal happens a few times until it fails.  I checked the Event Log for the Gateway and it publishes notices of expiration and renewals up until a renewal fails.

 

I called Tech Support and we discussed if a static IP would solve the problem.  Well, the only way to get a static IP is to change my service over to Comcast Business.  I don't know if my tech agent did a no-no but he was able to get a Comcast Business tech support agent on the phone.  He said that the best solution is to buy my own cable modem and have my router get the WAN address directly from teh network.

 

I OK with that as it would save money in the long run but it is frustrating that a Bridge Mode functionality is offered on the Gateway with support pages describing how to set it up and everything, yet it doesn't work and the workaround is to ditch the equipment.

 

There are two problems with buying my own cable modem though:

1) I am a Triple Play customer, so I need an eMTA modem for Voice as well.

2) I have and Xi5 box for one TV and the Xi5 FAQ thread in the TV forum says that it will only work with the XFINITY Wireless Gateway.  I can't connect it to my own router.

 

I just wish the equipment would work as advertised but if I have to go my own way, can anyone help me understand what I neeed to buy and get to have my three services (Internet, TV, Voice) work?

 

Thanks.

 

Marc

Authorized Vendor

Re: Losing IP address from cable modem in bridge mode every two weeks


MarcG10 wrote:
I called Netgear support and they had me direct connect a PC to the gateway, then during the router setup, I needed to use the PC MAC address (IP spoof?) to get things working. Strange, but it worked.

 

You should not need to do this, but you do need to reboot the modem each time you change a device behind the modem when in bridge mode..  If you have a cable modem this would be the same thing, when you change routers behind the cable modem you need to reboot the cable modem so the CMTS knows of the change..  This is becuase your only allowed 1 IP address..

 

My guess is that Comcast makes you get a new IP every two weeks and that cause the problem, but that is a guess. I posted this same message in the Netgear forums and on the Comcast subreddit. Is there some way to fix this so I don't have this problem every other Friday morning?

 My guess is your spoofing the MAC address and the DHCP Server is not liking it.. I would try this...

  • Upgrade the Netgear to the latest build
  • factory reset the device
  • reboot the gateway (bridge mode)
  • reboot the Netgear once again or have it do a dhcp renew once the modem is online..

You should be getting the same IP as long as your device is online, as long as your router responds to the DHCP half-time and renew request..

 

-------------------------------------
Network Engineer, IP Engineer, Docsis..; the views expressed on this post are mine and do not necessarily reflect the views of my employer..

Gamer.. Living the dream one catastrophe at a time Smiley Happy ..
Frequent Visitor

Re: Losing IP address from cable modem in bridge mode every two weeks

Thank you for the reply ArrisTuska!

 

It lost connection again this morning.  I will try again using the exact steps you outline below and will report back.  I think have have done that befdore but I have restarted and factory reseted so many times taht I am not sure.

Frequent Visitor

Re: Losing IP address from cable modem in bridge mode every two weeks

Hi ArrisTuska,

 

Well, taht is the first time I have gotten teh Netgear router to get an IP address with its own MAC address.  That always bothered me.

 

I did check the Connection Status and the Netgear's DCHP lease is now 55 minutes or so.  I have usually seen anything reanging fro a day to 4 days. I tried to Renew the Lease and it stayed at teh same expiration time of 55 minutes.  I guess we will see soon how well it renews on its own.  I will monitor and update.

 

MarcG10

Frequent Visitor

Re: Losing IP address from cable modem in bridge mode every two weeks

ArrisTuska,

 

Sorry for the rapidfire updates but the router successfully renewed its lease for 4 days.  I will continue to monitor but I am finally cautiosly optimistic.

 

MarcG10

Authorized Vendor

Re: Losing IP address from cable modem in bridge mode every two weeks


MarcG10 wrote:

ArrisTuska,

 

Sorry for the rapidfire updates but the router successfully renewed its lease for 4 days.  I will continue to monitor but I am finally cautiosly optimistic.

 

MarcG10


During maintenance windows the lease time is set to 1 hour other then that it should be about 4 days..  we will see what happens in about 2.5 days..  you should see a half-time renew

-------------------------------------
Network Engineer, IP Engineer, Docsis..; the views expressed on this post are mine and do not necessarily reflect the views of my employer..

Gamer.. Living the dream one catastrophe at a time Smiley Happy ..
Frequent Visitor

Re: Losing IP address from cable modem in bridge mode every two weeks

Hi ArrisTuska,

 

Last night, the half time renew was successful and right on time.  I have cut and pasted your solution here and added one step for the Netgear router:

 

My guess is your spoofing the MAC address and the DHCP Server is not liking it.. I would try this...

  • Upgrade the Netgear to the latest build
  • factory reset the device
  • reboot the gateway (bridge mode)
  • reboot the Netgear once again or have it do a dhcp renew once the modem is online..
  • it seems the Netgear needs the gateway to be rebooted after the first attempt to get an IP, so I just rebooted it a second time and the router was able to pick an IP.

You should be getting the same IP as long as your device is online, as long as your router responds to the DHCP half-time and renew request.

 

I believe the the Netgear router is not consistently forming the DCHP renew request correctly when it is configured to MAC spoof.  I had a thread going in their community on this issue and described the problem and suggested they investigate.

 

Thanks so much for your help.

 

MarcG10

Frequent Visitor

Re: Losing IP address from cable modem in bridge mode every two weeks

I am having essentially the same problem, which is a real pain because I have security cams that need the IP address in the android software to access the cams remotely.

 

What is the status of this thread?  Did the workaround create a stable situation?  I have had a fixed IP for abouat a year on my FL account, and for years on my MI account.  This change came from where and for why?

Unhappy Comcast customer