IPv6 R7800 wifi Android DNS/TLS/IMAP stops working

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tzr916

Occasional Visitor
EDIT Topic Title to reflect new information -> IPv6 DNS related see:


Very odd issue after changing to an R7800 router. I have always been able to use an android phone app to check my comcast pop email at home when on my wifi. And I could do the same when not at home using 4G mobile data. Then when I get back home, the phone automatically reconnects to my home wifi and I can again check my email.

That last part is the problem, after I have been out using 4G mobile data, I return home, the phone reconnects to my wifi, and now the pop email phone app fails - just spins never getting the new mail. Meanwhile, everything else on the phone works - gmail, yahoo mail, youtube, google play, etc. The only way I can get the android phone app to work again is to reboot the phone.

Some things that I have tried that do NOT help:
-tried several different pop email apps.
-tried switching the phone from my 2.4GHz wifi to my 5GHz wifi.
-turn wifi off / on in the phone.
-turn airplane mode on/off in the phone.
-uninstall / re-install the app on the phone.
-adding wifi to battery exclude.
-turn on "mobile data always on to allow for faster switching".
-try my GF's phone (different brand/model).

Also note, after the app is not working on my wifi, if I connect to the neighborhood comcast wifi it does work! Then I switch back to my wifi and the app fails again.
Sometimes, if I manually turn my phone's wifi off BEFORE leaving the house and do NOT use the email app, and then manually turn wifi back on when I get home the app will work.
 
Last edited:

HELLO_wORLD

Very Senior Member
This is a very odd issue. Seems related to this particular android app that apparently fails to fully reset when going to one network to your home network, but you said it does it with any pop mail app?

Anyway, POP is using ports 110 and/or 995.

What firmware are you using, which version?
Any specific NAT rule?

I have A R7800, and use Android, iOS and Windows devices with multiple mail accounts, and never had a problem switching from 4G to WiFi or VPN to WiFi. I use IMAP though...
 

tzr916

Occasional Visitor
Ya, I've tried several different android email apps. Also ALL variations of IMAP/POP, ports, and security.

Router is just using stock netgear v1.0.2.68

Only have one Port Forwarding service rule for a Media Server PC.
 

Droidrat

Regular Contributor
I have had a similar issue (I also use Comcast). In my case, the apps that are sometimes difficult to connect are xFinity (the Comcast app) and Facebook. When either hangs (the throbber throbs continuously), I can get them to work by restarting EITHER the modem or the phone; the R7800 router isn't the issue. One of my network friends told me that this behavior results from the abandonment of net neutrality, and the problematic apps are the ones that have priority; their tokens aren't updating properly (I am sorry that I can't better describe the issue). If you try again (much?) later, the apps might work without a restart of either the phone or the modem.
 

HELLO_wORLD

Very Senior Member
I have had a similar issue (I also use Comcast). In my case, the apps that are sometimes difficult to connect are xFinity (the Comcast app) and Facebook. When either hangs (the throbber throbs continuously), I can get them to work by restarting EITHER the modem or the phone; the R7800 router isn't the issue. One of my network friends told me that this behavior results from the abandonment of net neutrality, and the problematic apps are the ones that have priority; their tokens aren't updating properly (I am sorry that I can't better describe the issue). If you try again (much?) later, the apps might work without a restart of either the phone or the modem.

Not sure it is the same problem as his appeared when he started to use his R7800. However, that is a good clue.
I don’t think the R7800 is the issue, but it might be part of it for him.

@tzr916 are you using one email address or do you have several ones using POP (I mean different servers/providers)? Maybe it is linked with the POP server that is not happy for whatever reason by the switch of network (some credential tokens issues). The fact that turning your phone WiFi off first is working sometimes is leading in that direction or something like that.
 

tzr916

Occasional Visitor
Some interesting posts! I actually upgraded my my comcast service to 1Gbps and purchased a new modem at the same time I got the R7800. That's when this issue started. So it very well could be a modem/comcast issue.

I have do have three comcast.net email addresses setup on the IMAP/POP app(s) and they all stop working. I will definitely try setting up some different email providers in within the IMAP/POP app, but I do know that the NATIVE apps for gmail and yahoo email services do not ever have this issue.
 

tzr916

Occasional Visitor
So just for kicks, before I left for work this morning, I rebooted my comcast modem. Ten minutes after the modem was back up, a lot of my devices still reported no internet. When I accessed the router admin I saw a big red error on the internet, so I ended up having to reboot the R7800 to get everything back online.

I went to work, accessed the email app via 4G mobile a few times. Just got home and surprisingly it is working on my wifi! First time in months... Just wonder how long it will last, or how often I might be rebooting my modem/router.
 

tzr916

Occasional Visitor
Well that lasted all but 24hours. Just got back home from the grocery store and I'm back to square one, the adroid imap/pop email won't connect. I also just tried the native "xfinity connect" email app and it's not connecting either.
Next test is to add some non-comcast emails to the android imap/pop app.
 

tzr916

Occasional Visitor
Next test is to add some non-comcast emails to the android imap/pop app.
Well the problem affects non Comcast email also!
If I connect to the local "xfinity wifi" the imap/pop apps work, switching back to my R7800 no go...
 

tzr916

Occasional Visitor
Except when the phone apps don't work, I can continue to use my wifi to check email on my Laptop (thunderbird IMAP/POP email client same port/authentication). Of course my laptop hasn't really ever left my wifi network for any amount of time, joined a mobile network, then rejoined wifi.
 

R. Gerrits

Senior Member
Time to pullout wireshark??

Or seeing that you have android, I'd then install some DNS lookup tool (or SSHserver)
- use DNS lookup tool (or SSH into android) to see to which IP address the DNS-name of the pop3-server is resolving. Compare this between WiFi and 4G. (perhaps with a reboot in between.) Perhaps also compare to an nslookup on your laptop.

A wild guess -> they use different IP-address for POP3 when on their own network vs from an external network.
Your phone is caching the IP-address corresponding to the external access. And Comcast is blocking (or misrouting) traffic from their internal network to that external IP.

After a reboot of your phone (or a long wait) the cached DNS entry is deleted and then it starts working again.

Allthough this does not entirely explain why you claim it also affects nonComcast addresses.
Unless the mail-app is so buggy that it hangs on the first comcast mailbox, and never even tries the other mailboxes.
Did you try with only non-comcast mailboxes?

And it also not really explains why the other way around does always work. (first checking via WiFi and later checking via 4G.)


In the case where it is not related to split DNS. Then try to do a netcat (nc) from your android to the IP address of the pop3 server, on port 110 or 995 (whatever you have filled in in the email app)
I.e. confirm if it is really a TCP issue.
 

tzr916

Occasional Visitor
Ok, so first quick observation. I installed Whois DNS Lookup app on my phone. Verified the DNS Lookup works on my wifi, changed to 4G verified again it works, changed to local xfinity wifi verified it works, back to 4G-works, back to my wifi and BANG - DNS lookup tool HANGS never resolving. Go back to the email app and it does fail. Switch back to local xfininty wifi, everything works.... repeat.

Note: When in fail mode, the DNS Lookup also fails for outlook.office365.com via R7800.

When DNS Lookup does work, the ip addresses for comcast are a list of 16 IP addresses.

Phone (R7800):
96.117.2.221
96.117.3.101
96.117.3.110
96.117.3.112
96.117.3.119
96.117.3.125
96.117.3.131
96.117.3.132
96.117.3.137
96.117.3.138
96.118.128.111
96.118.128.145
96.118.129.174
96.118.129.21
96.118.129.48
96.118.129.71

phone (local xfinity wifi):
96.117.2.221
96.117.3.101
96.117.3.110
96.117.3.112
96.117.3.116
96.117.3.119
96.117.3.125
96.117.3.131
96.117.3.132
96.117.3.137
96.117.3.138
96.117.3.143
96.118.208.65
96.118.208.74
96.118.208.80
96.118.210.142

Phone (4G)
96.117.82.17
96.117.82.31
96.117.82.42
96.117.82.43
96.117.82.50
96.117.82.55
96.117.82.58
96.117.82.60
96.117.82.61
96.117.82.73
96.118.242.154
96.118.242.204
96.118.242.233
96.118.242.239
96.118.247.153
96.118.252.121

PC (R7800):
96.118.242.226
96.118.242.233
96.118.242.239
96.118.252.121
96.118.247.153
96.118.242.204
96.118.242.154
96.118.242.217
96.118.242.218
96.118.242.221
96.118.242.207
96.118.242.201
96.118.242.209
96.118.242.236
96.118.242.223
96.118.242.208


 

tzr916

Occasional Visitor
And even crazier - when in fail mode (R7800 wifi imap/pop email doesn't work), the DNS Lookup app on the phone hangs/fails for ALL web addresses!
www.google.com
www.sony.com
www.nbc.com
etc......

Yet, I can use a browser (firefox) app on the phone to open these pages just fine????
 

R. Gerrits

Senior Member
I guess you found the cause...
The reason why Firefox still can browse -> I suspect that Firefox uses DNS-over-HTTPS and is completely bypassing the DNS-resolver on the R7800.

In the meantime, a workaround -> change your WiFi setting on the phone, to use manual DNS servers, and enter the DNS servers you want to use / trust. (for instance you could use Cloudflare (1.1.1.1) or Google (8.8.8.8) )

Question now is: Why is DNS resolver on R7800 failing.
Do you use DNS-Crypt or AdGuard?
If not, you need to check if it is dnsmasq that is hanging, or if it is the upstream DNS servers from your provider that have the issue?
(can you still resolve routerlogin.net ?? -> then dnsmasq is working)
 

HELLO_wORLD

Very Senior Member
I think the problem is on the phone and not the R7800...

When on fail mode, your DNS lookup is fine from laptop, right?

Going to 4G then back to WiFi, the phone does not set up correct DNS (or does not receive it properly via DHCP.
 

R. Gerrits

Senior Member
I think the problem is on the phone and not the R7800...

When on fail mode, your DNS lookup is fine from laptop, right?
You have a point there. Was distracted when I reacted. I thought I read, that it also didn't work on laptop. But that is not mentioned anywhere.

And if it starts working again after a reboot of the phone, then it is even more likely to be a phone issue.
Still strange though...
 

HELLO_wORLD

Very Senior Member
You have a point there. Was distracted when I reacted. I thought I read, that it also didn't work on laptop. But that is not mentioned anywhere.

And if it starts working again after a reboot of the phone, then it is even more likely to be a phone issue.
Still strange though...

Yes, very strange. You may not be completely wrong as the router may fail to send the correct (DNS) info to the phone (DHCP).

The setup is also not the simplest with the Comcast modem behind that can mess things by blocking ports.
 

tzr916

Occasional Visitor
Laptop is always unaffected. The problem has been duplicated on my GF's android phone.
Next up - try manual DNS servers on the phone. If this works, is it some conflict with the R7800 or the Comcast modem?
 

tzr916

Occasional Visitor
Next up - try manual DNS servers on the phone. If this works, is it some conflict with the R7800 or the Comcast modem?
Did not help!!! Set manual DNS servers on the phone for 2.4Ghz and 5GHz R7800 wifi. Reboot phone, then:
-With phone connected to the 2.4GHz R7800 wifi, successfully use DNS Lookup app to find www.google.com
-Change to local xfinity wifi, lock screen, wait a minute, unlock screen, successfully use DNS Lookup app to find www.google.com
-Change to 2.4GHz R7800 wifi, DNS wait a minute, unlock screen, Lookup app FAILS to resolve www.google.com
-Change to local xfinity wifi, wait a minute, unlock screen, successfully use DNS Lookup app to find www.google.com
-Change to 5GHz R7800 wifi, DNS Lookup app FAILS to resolve www.google.com
-repeat . . . .

Also note that I never touched the IMAP/POP email app after the reboot.
 

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