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Re: Lose connection while modem renews internal DHCP?

I am having the same problem. 

My circuit was installed on November 20, 2019, and the first renewal of the address on erouter0 interface in the DP3941 happened on December 7. After that, DHCP lease time dropped to 12 hours. Every time address on the erouter0 interface is renewed, all connections through the modem are dropped for about 10 min. 

 

2019/12/19 20:46:59 Notice [Dhcpc][1620]: erouter0 got new IP 98.248.24.119

2019/12/19 11:02:54 Notice [Dhcpc][16631]: erouter0 got new IP 98.248.24.119

2019/12/19 10:52:23 Notice [Dhcpc][11759]: erouter0 got new IP 98.248.24.119

2019/12/18 17:08:06 Notice [Dhcpc][1413]: erouter0 got new IP 98.248.24.119

2019/12/18 12:50:15 Notice [Dhcpc][825]: erouter0 got new IP 98.248.24.119

2019/12/18 12:42:08 Notice [Dhcpc][29279]: erouter0 got new IP 98.248.24.119

2019/12/18 12:32:09 Notice [Dhcpc][24686]: erouter0 got new IP 98.248.24.119

2019/12/18 11:34:50 Notice [Dhcpc][1733]: erouter0 got new IP 98.248.24.119

2019/12/18 11:16:26 Notice [Dhcpc][17664]: erouter0 got new IP 98.248.24.119

2019/12/14 00:01:40 Notice [Dhcpc][14029]: erouter0 got new IP 98.248.24.119

2019/12/13 05:50:00 Notice [Dhcpc][26442]: erouter0 got new IP 98.248.24.119

2019/12/13 00:31:58 Notice [Dhcpc][4171]: erouter0 got new IP 98.248.24.119

2019/12/7 11:17:53 Notice [Dhcpc][1778]: erouter0 got new IP 98.248.24.119

2019/11/20 13:54:50 Notice [Dhcpc][1622]: erouter0 got new IP 98.248.24.119

2019/11/20 13:48:04 Notice [Dhcpc][4696]: erouter0 got new IP 98.248.24.119

2019/11/20 13:42:10 Notice [Dhcpc][1646]: erouter0 got new IP 98.248.24.119

 

 

Now the WAN Status page of the modem shows Lease expiration time in less than 10 hours:

 

DHCP Lease Expire Time (IPv4):0d:9h:54m

 

That means that I will go through another 10-minute connectivity outage in about 10 hours.

 

I understand that this DHCP address on erouter0 interface in the modem is the unfortunate part of how Comcast designed their static IP solution. For whatever reason, Comcast is not capable of routing to my static IPv4 address through a modem in raw bridge mode, that is why this dynamic address 98.248.24.119 on the erouter0 interface is needed, while my static network 50.250.224.244/30 is on the LAN side of the modem.

So why DHCP lease time was dropped suddenly from several weeks to hours? Is it possible to set it back to what it was before? 

 

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New Contributor

Re: Modem randomly reboots

For posterity, when someone digs up this thread several years later looking for solution which was not provided, here is how it was fixed.

DHCP renewal is just a red herring. It is a consequence of soft reset of DPC3941B. Soft reset is not recorded in event logs. The real problem, this Cisco device went bad over the time and was resetting itself. Each reset produced this infamous line in event log: "[Dhcpc][xxx]: erouter0 got new IP xxx.xxx.xxx.xxx". When technician came to replace DPC3941B, he showed me the logs from Comcast (CMTS) side, which contained tons of registrations (as a result of soft reset) and DHCP renewals. DPC3941B was replaced by a new one, and no resets for two days already. 

 

DHCP renewal, on the other hand, is quite benign. As long as the address stays the same (and it does, as it is bound to modem MAC address), when lease expires, its expiration is updated, but interface is left intact, not disrupting any connections.

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New Contributor

Re: Modem randomly reboots

It's 2019, and I am having exactly the same problem with recently installed Cisco DP3941. Was the problem resolved by replacing cisco with SMC? If so, I wonder if SMC modems are still available.

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Contributing Member

Re: Lose connection while modem renews internal DHCP?

Yes, that's right, Kastus. When a modem is in bridge mode, the Static IP routing, LAN DHCP and other settings are disabled. A bridged modem will only assign dynamic public IPs to connected devices in the same manner as a basic cable modem. 

 

When my lease expires, I lose connection for a bit too, but only for about 2 minutes or so. My current lease time is 7 days. 

 

You can change your DHCP lease time via the settings in your modem. Are you using a comcast BWG gateway? If so, you can log into the modem and change the lease time under the section: Local IP network

 

Ken

 

 

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New Contributor

Re: Lose connection while modem renews internal DHCP?

Thank you for looking, Ken. 

 

I am afraid it's a bit of misunderstanding. 

 

I have a static IP address, and the modem (DP3941) provided by Comcast is in "passthrough" mode. Modem is *not* issuing dynamic IP addresses to the connected devices. The only connected device is my firewall, and it has its IP address statically configured.

My static IP address is in 50.250.224.244/30 subnet, out of which 50.250.224.245 is on my firewall, and 50.250.224.246 is on the gig interface on the DP3941.

Now, on the cable side, interface erouter0 is assigned a dynamic address by Comcast, the address is always the same 98.248.24.119, and it is provided by Comcast. Default gateway on the cable side is 98.248.24.1. 

Back in November, the address 98.248.24.119 was issued with lease time at least several weeks. I did not know how to look it up in DP3941 at that time, so it is only my conjecture, as the address renewal did not happen until December 7.

Now, when I look at Gateway->Connection->WAN Status page, I see 

DHCP Lease Expire Time (IPv4):0d:22h:14m

This expiration is provided, by Comcast, it is not something configured in the modem. When lease expires, the address will be renewed (to the same one), and it will disrupt all connections going through the modem.

The lease expiration time dropped from weeks to hours on December 18. I wonder why it happened, and if it is possible to revert it back to several weeks.

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Contributing Member

Re: Lose connection while modem renews internal DHCP?

Kastus, thanks for reminding me, totally forgot that you had bridge mode enabled and probably had manual routing on via your router. 

 

Have you taken a look at the DHCP settings on the router since it's disabled on the modem? I'm curious as to, if none of your network settings have changed, why the lease changed. 

 

Do you mind if I take a closer look? Can you send me a private message with your full name, address, and account number/MAC address via private message so I can check things out? 

 

Ken

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New Contributor

Re: Lose connection while modem renews internal DHCP?

Ken,

 

Please go ahead and take a closer look. I sent requested details in a private message.

 

Thanks!

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Official Employee

Re: Lose connection while modem renews internal DHCP?

Thanks for the information. I really appreciate it. I'll definitely take a dive into this for you. Thanks for giving me the information. Just to verify, how many modems/routers are being used at this location? -Rob K. 

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New Contributor

Re: Lose connection while modem renews internal DHCP?

It's a single DPC3941B in passthrough mode. Firewall with static IP address is plugged in LAN Ethernet port 3.

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Official Employee

Re: Lose connection while modem renews internal DHCP?

Hi there, and thank you for taking the time to share your feedback. You've reached the right place, and my goal is to change your experience. Can you please send me a private message with the last four of the account number and/or last statement balance, your full name, phone number, and service address including city, state, and zip code? –Rob K.

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Official Employee

Re: Modem randomly reboots

I am very sorry to say that we do not have SMC modems available any longer. I am sorry to hear that you are having trouble with your modem. I would love to assist with the modem issue Can you please reach out through private message with your first and last name, full service address and account number or phone number? 

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New Contributor

Re: Modem randomly reboots

Now the modem didn't even last till address expiration time and renewed it multiple times:

 

2019/12/22 07:12:13 Notice [Dhcpc][12601]: erouter0 got new IP 98.248.24.119

2019/12/22 06:01:33 Notice [Dhcpc][17636]: erouter0 got new IP 98.248.24.119

2019/12/22 05:40:20 Notice [Dhcpc][8694]: erouter0 got new IP 98.248.24.119

2019/12/22 04:25:36 Notice [Dhcpc][12366]: erouter0 got new IP 98.248.24.119

2019/12/22 03:42:53 Notice [Dhcpc][27946]: erouter0 got new IP 98.248.24.119

2019/12/22 01:50:21 Notice [Dhcpc][17683]: erouter0 got new IP 98.248.24.119

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New Contributor

Re: Modem randomly reboots

For posterity, when someone digs up this thread several years later looking for solution which was not provided, here is how it was fixed.

DHCP renewal is just a red herring. It is a consequence of soft reset of DPC3941B. Soft reset is not recorded in event logs. The real problem, this Cisco device went bad over the time and was resetting itself. Each reset produced this infamous line in event log: "[Dhcpc][xxx]: erouter0 got new IP xxx.xxx.xxx.xxx". When technician came to replace DPC3941B, he showed me the logs from Comcast (CMTS) side, which contained tons of registrations (as a result of soft reset) and DHCP renewals. DPC3941B was replaced by a new one, and no resets for two days already. 

 

DHCP renewal, on the other hand, is quite benign. As long as the address stays the same (and it does, as it is bound to modem MAC address), when lease expires, its expiration is updated, but interface is left intact, not disrupting any connections.

View solution in original post

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