Same here. Also on V1 with Comcast. I never had any problem before. I've tried everything with this new firmware - it just doesn't work with Comcast ipv6. The good news is just leaving everything default after a reset works fine, but I'd rather use ipv6 since Comcast provides it.

That is good (and bad) to know. I have been hounding Comcast thinking they were the problem. At some point IPv6 started working again and worked for about four days. IPv6 seems to have stopped working again when the lease expired on the IPv6 address and prefix delegation (PD). Funny thing is, I connected my laptop directly to my modem and never got an IPv6 address there either which made me think even more that the issue was with Comcast. I have always used Cisco and Linksys routers in the past, and I switched to TP Link because Linksys routers are so expensive and now just plain ugly. I have been thinking about getting a Netgear Nighthawk AC1750 as I hear they are more reliable. I don't need anything bigger than AC 1200 because Internet download speed is only 100 Mbps and router only has GigE ports anyway. Why do I need anything more than 1.2 G bps (1200 Mbps) WiFi? It's like buying SFP 50 sunblock when SFP 30 blocks 99.7%. Its all marketing. Unfortunately, I can't find a cheapr Netgear AC 1200 that I like. Thanks for the info and good luck.

Paul:

Your unwillingness to entertain the possibility that the new firmware is the problem after all of the evidence I have presented reinforces my decision to switch to Netgear. My IPv6 access has been down for over a week, and I cannot wait any longer for resolution because I am a network engineer and must have IPv6 access for work. These facts below are indisputable:

-IPv6 worked fine on my C1200v1 for almost two years on firmware C1200(US)_V1_170413 and previous versions
-IPv6 no longer works on my C1200v1 on firmware C1200(US)_V1_180103
-IPv6 stopped working on my C1200v1 a few days after upgrading to firmware C1200(US)_V1_180103 when the IPv6 lease expired, and the C1200v1 will not or cannot renew it
-No setting was changed on my C1200v1 prior to or after upgrading to firmware C1200(US)_V1_180103
-Other TP-Link customers are reporting in the TP-Link support forum that IPv6 stopped working after upgrading to firmware C1200(US)_V1_170413
-IPv6 works on my new Netgear Nighthawk AC1750 right out of the box

http://forum.tp-link.com/showthread.php?104073-IPv6-No-Longer-Working-after-Firmware-Upgrade-on-Archer-C1200&highlight=IPv6

I understand TP-Link tests new firmware before release, but testing does not guarantee that no new bugs are introduced. In fact, I just noticed TP-Link released newer firmware C1200(US)_V1_180123 which includes "Modifications and Bug Fixes." Did TP-Link specifically test this new firmware with Comcast, America's number one cable provider?

You may close this case.


TP-Link Support:

Hi, Paul
The reason why I suggest you downgrade the firmware is that I want you make the comparing testing, to help me confirm some information. I didn’t think the new firmware is broken, and don’t want you use the previous firmware in the future. I just want to find out the problem and fix it if it exist.

Thanks for your understanding!


Paul:

It cannot be anything but a firmware bug because IPv6 stopped working right after I upgraded to the latest firmware. IPv6 worked for almost two years on previous firmware. I made no configuration changes before or after firmware upgrade. I have sent you screenshots of the configuration. And now IPv6 works on a different router just fine. I set it up with no problem like I did the c1200. I do not believe the problem is a simple setting after working for two years. I think your last email suggested I downgrade the firmware.


TP-Link Support:

Hi, Paul
I'm pretty sure it's not a broken firmware because every firmware need pass our testing process before being released.
So there must be any simple setting fault or some other reason cause this problem and I'm also willing to help you about it.
But do you mean you have refund this C1200 of yours? Or it is still in your home? Thanks!


Paul:

I replaced the Archer C1200 with a Netgear Nighthawk AC1750, and IPv6 immediately started working and continues to work.

I have lost faith in TP-Link for releasing buggy firmware that broke the most basic functionality of the router. IPv6 is not an “advanced” feature. IPv6 is the future of the Internet. The Internet is dead without IPv6.


TP-Link Support:

Hi, Paul
I will follow your case from now on. As you router's IPv6 works normally before, I'd like to remotely help you to solve it, would you mind installing a software named "Teamviewer"?
If not it would also be OK, and then please downgrade the firmware to see if it works, thanks!


TP-Link Support:

Many thanks for your valuable reply.

Please login to C1200 web interface, go to advanced, send me screenshot of Internet page, I need to check IPv4 address. Thank you.
After get this information, I will escalate your case to senior engineer to do further analyze. Look forward to your reply.


Paul:

Yes IPv4 still works. No changes were made to the IPv6 configuration prior to or after the firmware upgrade. Internet connection type is set to Dynamic IP (SLAAC/DHCPv6), Get IPv6 address is set to DHCPv6, Prefix delegation is enabled, and DNS Address is set to Get dynamically from ISP. I no longer get a WAN IPv6 address assignment or a prefix delegation for my local network. This all started happening two days after upgrading the firmware. Comcast is my ISP, and they say there is no problem. I have spoken to several other people in my neighborhood with Comcast Internet service who are not having any IPv6 issues, but they do have various other brand routers, i.e. Linksys, Netgear, etc.


TP-Link Support:

Thank you very much for your email requesting information about our product.

After upgrading firmware, is IPv4 still working? Please login to C1200 web interface, go to Advanced--Status, send me screenshot of the whole page.
Then go to IPv6, configure IPv6 as below:
Internet connection type: Dynamic IP (SLAAC/DHCPv6)
Click Advanced, choose Get IPv6 Address as DHCPv6, save. Then send me screenshot of the whole page.

Then connect computer to the router via Ethernet cable, go to control panel--network and internet--network and sharing center--change adapter settings--Ethernet--Status--details, send me screenshot of details page.


Paul:

IPv6 is no longer working after upgrading the firmware on my Archer C1200 router to C1200(US)_V1_180103 from C1200(US)_V1_170413. Comcast is no longer able to assign an IPv6 address to my router or a /64 prefix delegation for my local network. I have rebooted my Zoom 5370 modem and C1200 router multiple times. I have contacted Comcast, and they have reset my modem and see no IPv6 issue in their network. Other Comcast customers in my neighborhood are not having any IPv6 issues. I am a network engineer and need IPv6 access for work. Please help.

The new firmware (I think it's 180123) that was just released fixed the ipv6 problem. Works great now. 19/20 on ipv6 test website.

EDIT: Nevermind. I reset the router initially and it worked. Then I did a full reset again, did not change any other default settings except ipv6, obviously, and no ipv6. Same as before. It's still just as hit and miss. You may luck out every once in a while.