IPv6 routing on DPC3941B in pass through mode

I am having the same issue. I have statics and my IPv6 was working fine until recently.

I suspect that comcast broke the DPC3941B's ipv6 with a firmware upgrade similar to theCGA4131COM. I was hoping comcast would come up with a solution by now since this has been a know issue for some time.

It seems holmosapien is not willing, or allowed, to share the eventual solution with us. It is great to hear better training materials will be provided, but as long as things don't actually get fix that is useless.

Today I ran into this problem. I had a NetGear CDR 3000, but along with a contract (also going from 75 -> 100) renewal was forced into a modem replacement (I did not want it, but was forced). Swapped the modem, waited for firmware updates and static IP confiration while tech waited. Confirmed all that was working, but IPV6 was not!

I plug my EdgeRouter into the modem's LAN port and the EdgeRouters WAN side is configured with one of my static IPs. IPv4 works fine. Investigaation with packet sniffing confirms the very same problem. Prefixes are received, but not properly routed by Comcast Technicolor CGA4131COM. It performs a neighbor solicitation instead. Nothing was changed on my LAN equipment, only the modem swap. Bleh!

So either there is an actual fix, or an equipment swap is needed to a model modem that handles this correctly. No matter what Comcast says, if it works correctly on the NetGear and on some other Comcast supplied devices but not the Technicolor CGA4131COM than that device is at fault and its firmware should be fixed!

I'm going to need a real fix from Comcast, or holmosapien if willing/able (DM is fine too), or an equpment swap. I have seen reports that the DPC3941B works, although it may introduce unwanted etra latency...

Thank you for your patience and for providing this information. We truly want to help and do everything we can to provide a fix for the IPV6 routing issues. Please feel free to send us a private message to further assist.

Keep in mind that I haven't been to the office in over three months so I don't know the current state of IPv6 support on the CGA4131COM, but when I was fighting all of this there were two issues at play:

1) Our modem could get an IPv6 WAN address that worked, but the delegated prefix was not being routed. This was not related to the modem, and happened with every modem Comcast gave us. This was an upstream network problem, and the only reason it took us over a month to get it fixed is because nobody at Comcast that we normal people are allowed to talk to understands layer 3 routing. They have a script that tells them to ping the WAN address, and when they can they give up and say "must be on your side!". I finally was able to escalate it to a different group that was allowed to talk to real network engineers who fixed the broken route.

2) Once the routing problem was fixed, I found that the CGA4131COM has broken firmware that, at least a few months ago, will not route IPv6 if you have a static IPv4 assignment. You can find Comcast representatives saying in this forum that it's a known issue and they would have a fix by the middle of November (2019!), but months later I couldn't even get the executive support guys to tell me what the status was. The only way I could get it to work was by putting the modem in bridge mode, which bypasses the IPv4 static. That frustrated our marketing guys because they liked being able to filter our IP address from our website statistics, but it was a compromise we could deal with.

I just SSH'd into a computer at the office and I notice that as of right now IPv6 is broken there, too. It could mean that our IT guy took the modem out of bridge mode, or it could mean that there's been a firmware update that has broken my site just like yours. I will tinker around with it more this coming week and see if I can come up with a working configuration.

Thanks so much for taking the time to reach out to us through our business forums. I very much appreciate your patience and greatly apologize for the delay in our response. I know how important the services are to your business and we want to do all that we can to assist. I am sorry to hear that you are having issues again with your static IP's. I can certainly review the modems settings for you and work on a resolution. Can you please reach out through private message with your first and last name, business service address and account number or phone number? 

I have a /56 static subnet for ipv6, and I believe I am having the same routing problem with the DPC3941B as well. I've been suspecting it's either a route issue with the modem, or an upstream route issue as well.

A linux router/firewall device is connected to the modem that's in pass-through, and it can auto-configure and route a /64 subnet on the external interface just fine. I can ping out to any ipv6 address from the router without a problem.

I have multiple vlans on internal interfaces that I can assign additional /64 subnets on, and these are delegated out to clients just fine. However, none of these devices are able to communicate past the router.

The internal devices can ping the router's external IP address without a problem, but they can't ping the modem's IPv6 address on the same /64 subnet as the router's external interface.  The router can ping the modem's address without any problems.

I've been able to use IPv6 with a Hurricane Electric tunnel for quite some time, using the same routing/subnet structure without a problem, but the moment I try to use the native IPv6 I encounter this routing issue. 

Hello, how are you? I hope overall your day is going well. Thanks for all the details about what you are experiencing using your service and third-party equipment. I need to make sure everything looks good with your modem and service. Are you able to send a private message so I can take a detailed look at your account? If you can include your name, service address, and account number this would be perfect. I can use the phone number listed on the account instead of the account number if that's easier. 

At our site we're back to experiencing the same issue.

We're provided a WAN address that works, but the LAN address that is provided by DHCPv6-PD isn't being routed. The symptoms are exactly the same as last time: I can ping out, the packets make it to their destination, but the return packets are being lost before they make it back to us.

Last time it took over a month to get it resolved because nobody that end-users are allowed to speak to understands layer-3 routing, and I have too much actual work to do to fight through this again. I am hoping that someone here can get this escalated to the same team that resolved this issue last time.

Hello, how are you? I hope overall your day has been a good one! I will be happy to provide the best possible support. Are you able to send a fresh private message so we can revisit your account? We will always have to do this if a lot of time passes. This will allow me to help concisely. Are you able to include your name, service address, and account number? (or phone number) 

Same issues for my configuration. Cisco DPC3941B was running fine with IPv6 and all of sudden stopped. Static IPv4 no issues. But, IPv6 hasn't been working now for a while. This https://forums.businesshelp.comcast.com/t5/IPV6/IPV6-routing-broken-following-package-upgrade/td-p/41521 says that it is a firmware issue. Would love to rollback and see if that corrects everything.

Good morning, thank you so much for taking the time out of your morning to reach out to the Digital Care Team here through the forums. I am sorry to see that you are having issues with your IPv6 routing on your device and we can take a look to help. Can you please send us a private message with your name, the full address, and the phone or account number? 

Did you ever get this fixed?  It's driving me insane.

Tier 2 support is looking at it. On my end I am getting this message "status message: Server support for prefix delegation is not enabled. Sorry buddy." Definitely an issue on the modem side of things. It was previously working, some oddities, but it was working.

Same issue as of yesterday here. Had to get my Cisco CM replaced with a new one that they called a "Technicolor" that seems to have a new firmware. My complaint is detailed here and is pretty much exactly the same as everyone else: 

I was up all night doing packet captures because I had it all configured exactly the same on the CM, and no changes on the same piece of my own hardware but it just didn't work at all. I thought for sure it was a routing issue until I took the PD out of the equation and it "just worked".

Basically if I request a PD, I get it, but the Cisco CPE that Comcast provides wrongly tries to do NS for the downstream delegated address space, which breaks it completely. My device should handle the ND/NS parts and the CPE shouldn't care as that is part of the layer2 process, and the route for the delagated prefix is just that, delegated to the downstream device.

Then I take a look at the forums and the problem appears to be widespread and due to firmware that is newer on the device they have on the replacement I was given.

So I can either have my static v4 addresses that I pay ~$300 a year for, no longer have static (or any IPv6) for OR dynamic everything with dynamic IPv6. Honestly, I don't care at all about the static IPv4. I pay for it to get a static IPv6 block.

This is 2020 and is fundamental stuff.