IPv6 R7800 wifi Android DNS/TLS/IMAP stops working

[R. Gerrits]

hmm strange...
Next step I would try: Use the debug page (routerlogin.net/debug.htm) to start a packet capture. (best to do that to an USB stick)
Then repeat the steps you did earlier. (best to make sure that as little devices as possible are connected to the R7800, to minimize the size of the capture)
Stop the packet capture and copy it to a PC.
Open it in Wireshark, and check the DNS packets that are sent.

And then I'm especially curious to which IP address the DNS packets are sent in the failure situation. (or if they are even sent)

 

[tzr916]

I did some captures, made them as short as possible. First time Wire Shark user, so I really have no idea what I am looking at.

Verified DNS Lookup broken on R7800 wifi, switched to local xfinity wifi and it works, re-connected to R7800 wifi and verified DNS fails, repeat...

After the fail, I rebooted ONLY the R7800, not the modem. The DNS lookups started working on my R7800 wifi. And still working even when switching the phone between R7800 2.4GHz & 5GHz - the local xfinity wifi - turning phone's wifi OFF/On. Now It won't break again until I leave the home for a significant amount of time.

For the Logs marked FAIL, the phone was IP 192.168.1.117
For the Logs marked success, the phone was IP 192.168.1.128

WireShark.zip

drive.google.com

 

[tzr916]

Strangely the phone will work on my Wifi about 50% of the time if I manually disable Wifi on my phone before I leave the house, and when I get home manually close all apps and enable Wifi on the phone.

I guess this is just gonna be "a thing" with this router, unless someone knows a WireShark expert who wants to help.

 

[R. Gerrits]

had a look at your wiresharks. Initially I couldn't really see anything wrong.
In both the fail and the success pcap, we see successful dns queries being made.
(try yourself with filter " (ip.addr == 192.168.1.128 or ip.addr == 192.168.1.117) and (udp.port == 53 or tcp.port == 53) "

But in neither I saw requests that belong to your email provider.
Also I could not see POP3 traffic (port 995).

Then I removed the ip filter, and only looked for tcp.port == 995 -> this time I did see something in the succes, but the traffic is not coming from the mentioned IPv4 address, but an IPv6 address....

In the fail, there is no tcp port 995.

Focussing on DNS via IPv6 -> in the success, with udp.port == 53, you see a lot of DNS requests also from IPv6 addresses, also for mail.comcast.net
In the fail, I see no udp port 53 traffic for IPv6

So the issue probably lies somewhere in the use of IPv6.
As a workaround, you could disable IPv6 on the router....

I'm not using IPv6 on my router, so cannot really help you there.
But I'm guessing that either dnsmasq on the router sometimes stops responding to dns queries. (you could perhaps test that with another device, although I don't know exactly how to do that).
Or the DHCPv6 on the router does not always properly send the correct DNS server entries.
Or the phone is having an issue with accepting the proper DNS server entries.
(not sure if you could also configure your phone to use a manual IPv6 DNS server (for instance 2001:4860:4860::8888))

 

[tzr916]

Looks like you hit on something with IPv6. I could not find any way to set the DNS Servers on my phone to IPv6 addresses, IPv4 yes but that doesn't help. So I completely disabled IPv6 on the R7800 and now my phone seems to be working fine. I can now leave my wifi, go to 4G, go to local comcast free wifi, get back on my wifi and DNS/IMAP works!

Wonder what settings in the R7800 would allow me to turn IPv6 back on?

 

[HELLO_wORLD]

Looks like you hit on something with IPv6. I could not find any way to set the DNS Servers on my phone to IPv6 addresses, IPv4 yes but that doesn't help. So I completely disabled IPv6 on the R7800 and now my phone seems to be working fine. I can now leave my wifi, go to 4G, go to local comcast free wifi, get back on my wifi and DNS/IMAP works!

Wonder what settings in the R7800 would allow me to turn IPv6 back on?

R7800 IPv6 is not great...

On the LAN side, dhcp6s is not able to attribute SLAAC+DHCP properly, and Android is not able to get IPv6 through DHCP.

I installed dhcpd through Entware and use it with -6 argument and my own config to serve IPv6 on my LAN the way I want (fixed IP for some devices, DHCP on others, SLAAC on Androids...)
Had to rewrite IPv6 scripts on firmware too.

 

[tzr916]

Thanks for the reply. I was hoping of something a bit simpler (and found in the OEM firmware). Oh well, I am just happy that I don't have to futz with my phone every time I get home!