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New Member


2 Messages

Mon, Jan 19, 2015 3:00 PM

Internet drops on IPV4 while IPV6 stays online

Since December last year I have problems with my Comcast SMC router (using Comcast Business Class Internet)


Several times during the day my IPV4 connection to the internet goes down while my IPV6 connection is still up.


If its down, I can still ping any internet address from the diagnostics screen on the Modem and it reports connectivity just fine.

But if I ping from my PC behind the modem (aka behind the Route in the SMC Modem), the ping fails.


That tells me that the SMC modem does not route properly anymore (aka is BROKEN).

So far non of the Comcast support engineers I tried to tell this understood what I am talking about.


Is there anybody out there who has the same experience?
How can I convince Comcast that there is a problem in the modem?

I had them exchange the modem in december but the new one does exactly the same problem.

To me this points at a Firmware issue of the modem.


I cannot use the Netgear modem as that modem is NOT able to turn off the IPV6 DHCP server in the modem and screws up my internal network (for some strange reason IPV6 DNS has priority over IPV4 DNS and I have my own DNS server for my inhouse PCs).


Does anybody have an idea what to tell Comcast or how to fix this?

New Member


2 Messages

7 y ago

Checking for ongoing issues with Comcast IPv6 & IPv4 and their provided Netgear CG3000DCR DOCSIS 3.0 Commercial Cable Modem and Router.


My Comcast Business service is supposed to be 150/20 without any static IPs.

I note consistent difference between IPv4 & IPv6

I started this morning (onrebooted laptop plugged into port 3 of the Netgear)

0815am IPv4 @ 25/21 & IPv6 @ 168/22

1300pm IPv4 @ 11/19 & IPv6 @ 136/23 -- On the phone with Comcast - they are sending a tech out tomorrow.

1715pm currenlty @ (refer to image)

Comcast SpeedTest 20150216-1300

Comcast should be giving me the same class of service over both, as IPv6 has not been universally adopted.

The disparity between my class of service over IPv4 and IPv6, as well as the gradual further degredation of performance, is very concerning.  Your thoughts on this matter will be appreciated.