Problem with ipv6 not working for clients

[Morac]

I have a RT-AC88U that was running Merlin 380.61 for about 7 months without issue. I have Comcast Xfinity and IPv6 native was working fine on all my LAN clients for that entire time. Today I rebooted the router to clear out the UPNP forwarding. Since doing so I've been unable to get IPv6 working on any of my clients. I can ping IPv6 addresses from router's network tools page and I can also ping my router's WAN IPv6 from the Internet, but I can't get anything LAN side working at all. I tried rebooting again. I tried turning IPv6 off and on. I even tried upgrading to 380.64 and still IPv6 isn't working.

As far as I can tell DHCPv6 is working as I can get addresses from domain. The clients seem to be getting IPv6 address, though I'm not sure this is correct. My WAN IPv6 starts with 2001:, while all my clients are getting 2601: which matches the LAN IPv6 Address. Is that correct?

All I know is that trying to ping any IPV6 site such as ipv6.google.com times out and going to an IPV6 only page also times out. This was working fine prior to the initial reboot.

Any ideas on how to diagnose what's wrong here?

 

[Morac]

Okay I'm not sure why this worked, but I turned off IPv6 on my router and disconnected it from my modem. I then plugged my computer directly into my modem (after rebooting it). I tested IPv6 and it worked fine. My computer got the 2001: IPV6 adddress.

I then enabled IPv6 Native on the ASUS, which obviously didn't get an IPv6 as it wasn't connected. I then disconnected my modem from my computer and rebooted it and waited for it to sync up and then connected the router to it. About 30 seconds later it got an IPv6 address (same 2001 WAN and 2601 LAN). I then pinged ipv6.google.com on my PC. The first ping failed, but then it started working. At that point IPv6 worked on all my LAN clients. I could ping and reach IPV6 web sites and incoming pings from the Internet to my LAN clients IPv6 addresses (which started 2601 worked.

So for whatever reason, even though all my clients got valid IPv6 addresses, the router wasn't routing the IPv6 LAN traffic to WAN or vice-versa. I have no idea why what I did would fix that.

I did have IPv6 stop working before, but rebooting the router got it back. This time rebooting broke it which makes no sense to me, nor why turning it off, and then back on when not connected to the Internet would fix it.

 

[Morac]

It is curious that the WAN and LAN addresses don't start with the same prefix. That seems to be the norm based on what I've read on numerous web sites.

Is the router picking the LAN address prefix or is that assigned by Comcast. If so why use a different prefix?

 

[buddyp]

It is curious that the WAN and LAN addresses don't start with the same prefix. That seems to be the norm based on what I've read on numerous web sites.

Is the router picking the LAN address prefix or is that assigned by Comcast. If so why use a different prefix?

comcast uses "prefix delegation" for its customers. They supply a separate prefix to your router via DHCPv6 and your router passes out addresses with that prefix out to your clients using "stateless auto-configuration" (SLAAC) or optionally, DHCPv6. If you like this sort of thing and want to learn more, hurricane electric has a free online course on IPv6.

https://ipv6.he.net/presentations.php

 

[Morac]

comcast uses "prefix delegation" for its customers. They supply a separate prefix to your router via DHCPv6 and your router passes out addresses with that prefix out to your clients using "stateless auto-configuration" (SLAAC) or optionally, DHCPv6. If you want to get all the details, google the phrases in quotes.

Thanks. Any idea why IPv6 routing simply stopped working after a reboot, even though the router and clients were getting IPv6 addresses and DHCPv6 still worked?

 

[buddyp]

Thanks. Any idea why IPv6 routing simply stopped working after a reboot, even though the router and clients were getting IPv6 addresses and DHCPv6 still worked?

without lots more data (routing tables, traceroutes, etc) there's no way to know. anyway its comcast /shrug

After I wrote the other reply, I saw your other question, why a separate prefix for delegation? I don't know the answer, and never really thought about it before, but now I'm curious. I may look into it if I have some free time. At my beach house where I have comcast the router prefix is 2001:: and the delegated prefix is 2600:: I assume yours is the same or similar

 

[Morac]

without lots more data (routing tables, traceroutes, etc) there's no way to know. anyway its comcast /shrug

After I wrote the other reply, I saw your other question, why a separate prefix for delegation? I don't know the answer, and never really thought about it before, but now I'm curious. I may look into it if I have some free time. At my beach house where I have comcast the router prefix is 2001:: and the delegated prefix is 2600:: I assume yours is the same or similar

Yes it is.

After my initial post, I found this post which details Comcast's IPv6 setup.

https://www.dslreports.com/forum/r28960304-