Skip to main content

  • Home

  • Getting Started

    • Offers

U
user_xbkrna
1st Topic
1st Reply

4 Messages

Friday, December 15th, 2023 9:45 PM

Closed

Issue with IPv4 when IPv6 is enabled Modem: MB8611

Hello,

I am running into an issue with IPv4 internet when I enable IPv6. The issue is that once ipv6 is turns on the modem will stop forwarding all traffic(IPv4 and IPv6). It will stay in this state until the modem is rebooted, however post reboot  traffic will drop again after about 2 minutes. If I turn off IPv6, IPv4 will work exactly as you would expect. This problem started after buying a MB8611 and still persists even after replacing the modem. The problem also follows other firewalls. I am kind of at a loss since Comcast support says they cant help and wont do anything. has anyone else ran into a similar issue?

Question

 • 

Updated 

1 year ago

170

2

0

Was this helpful?

BruceW

Gold Problem Solver

 • 

26.1K Messages

1 year ago

... issue with IPv4 internet when I enable IPv6 ...

Could you describe what you mean by "enable IPv6"? Since the 8611 is a straight cable modem with no router component, I don't think the device has a way to "enable IPv6" (but I couldn't find a full manual for it so maybe it has some sort of IPv6 option?).

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

3

0

user_xbkrna

4 Messages

Hello @BruceW thank you for the response!

On my firewall I simple hit hit a check box that enable enables IPv6. When I do this the firewall will pull an address, but after a couple minutes ALL traffic will stop forwarding. I can do a packet capture on my firewall and I can see traffic leave the firewall nothing ever comes back. so it is like the modem or comcast stops forwarding. Its worth noting that this same firewall config worked with an older SB6121 I had prior to upgrading to the MB8611. This issue started after with the new modem series.  

1 year ago

0

flatlander3

Problem Solver

 • 

1.5K Messages

@user_xbkrna​  What are you using for a firewall?  I ask because there are some oddities with IPV6 and pfSense/opnSense and comcast. 

If it's some other equipment, if there was a network "upgrade" in your area, you might be locked to a /64 prefix delegation size now.  You used to be able to hint for something else like a /56.  Now hinting for that breaks stuff. 

1 year ago

0

user_xbkrna

4 Messages

Hello @flatlander3​ 

I am currently running a Cisco FTDv. I have also tried a Cisco ASA and opnSense firewalls. they all run into the same symptom. I have been trying prefix delegation, but the thing is I don't even have to have a real ipv6 configuration for it to break. This interface config is enough to cause it.

interface TenGigabitEthernet0/0
 nameif outside
 cts manual
  propagate sgt preserve-untag
  policy static sgt disabled trusted
 security-level 0
 ip address dhcp setroute
 ipv6 enable

I just have to have the firewall generate a link local address and report joining the multicast addresses for it to break. 
  Joined group address(es):
    ff02::1:ff4b:69ae
    ff02::2
    ff02::1

turn it on will cause break traffic right away, rebooting the modem will allow it to work for about 2 minutes, then it goes back to broken. If I disable IPv6, IPv4 will just work...super frustrating, because IPv4 should just work even if IPv6 is misconfigured. 

(edited)

1 year ago

0

user_xbkrna

4 Messages

1 year ago

so just to add to this maybe it might help someone else, although it not a great option. I replaced the modem with a SB6190 and now IPv6 works for me. so something with the modem / comcast is the problem, just not sure what. 

0

0

forum icon

New to the Community?

Start Here