Mysterious loss of connectivity

[Lynx]

Thanks a lot for this insight. Any idea what the significance of the port scan is? Also why does modem restart every 48 hours?

I am using on VPN client: accept DNS configuration: exclusive because then the pushed DNS servers from NordVPN get used by my router and this means Amazon Prime doesn't detect VPN. I also have force internet traffic through tunnel: Yes.

Why would DNS not working cause everything else to fail I wonder.

 

[ColinTaylor]

Any idea what the significance of the port scan is?

What port scan? OK I see now. You've added a whole load of extra information that wasn't there the last time I looked.

Also why does modem restart every 48 hours?

This is fairly typical for mobile connections. The mobile network isn't really designed for permanent connections. I think the mobile operators do this to prune zombie connections and free up wasted resources.

Why would DNS not working cause everything else to fail I wonder.

Some of router startup processes rely on being able to resolve DNS names and to connect to the internet, e.g. NTP. If you don't have a working DNS you'll have problems.

 

[ColinTaylor]

It would be useful to know what the public IP address of your connection is (not the private 10.241.204.243 address) before and after this problem occurs. www.whatsmyip.org

 

[Lynx]

Wouldn't it just be my VPN public IP before and then no IP after because the router fails to regain connectivity?

Seems like solution might be to have DNS not exclusive but whichever is the appropriate setting such that the VPN pushed DNS is favoured and otherwise the ISP pushed DNS is the fall back. Any idea what setting that is?

 

[ColinTaylor]

Wouldn't it just be my VPN public IP before and then no IP after because the router fails to regain connectivity?

I meant the public IP address of the modem connection (i.e. without the VPN enabled). And then again after you've rebooted the router to regain the connection, again without the VPN. I'm trying to see whether the mobile operator is changing your public IP address when the modem resets after 48 hours.

Seems like solution might be to have DNS not exclusive but whichever is the appropriate setting such that the VPN pushed DNS is favoured and otherwise the ISP pushed DNS is the fall back. Any idea what setting that is?

No idea. I've lost track of all the different combinations and interactions of the VPN DNS options.

 

[mac.mc78]

I have the same router as you, but I have NO special setup in Merlin at all.

Pretty much all 'out of the box' settings, apart from things like a couple static IP clients, etc.

I am experiencing the exact same thing as you - My setup will work for a few days, and then all of a sudden the internet goes dead. Local network is working fine, as my NAS stays active, etc.

Its ironic that you're describing the exact same scenario as me, and I have the same Router, just a different setup.

 

[Lynx]

I meant the public IP address of the modem connection (i.e. without the VPN enabled). And then again after you've rebooted the router to regain the connection, again without the VPN. I'm trying to see whether the mobile operator is changing your public IP address when the modem resets after 48 hours.

My modem is set to operate in bridge mode so it shouldn't pick up a WAN IP itself - the Asus Router should though. Ah, I understand now. I presume this is a CG-NAT thing along the lines that it cycles the public IP and all the local IPs associated with that public IP every 48 hours?

Do you know what the significance of the modem talking about blocking port scan from VPN is? Couldn't this mean the modem is blocking some important functionality relating to OpenVPN? I'm confused because since this is CG-NAT surely it's not as if somehow the VPN is able to initiate a connection all the way to my router from outside? Anyway the modem blocking something from happening in respect of OpenVPN seems troubling, no? I am keen to understand this to know if I should disable firewall in the bridged router (modem).

On the DNS theory, could it be that when Asus router reboots it first takes on DNS from ISP and then initiates VPN session whereas with just simple WAN restart it is not taking on the DNS from ISP and so stuff fails? I am trying to understand why rebooting router works but the WAN restart process fails.

I have the same router as you, but I have NO special setup in Merlin at all.

Pretty much all 'out of the box' settings, apart from things like a couple static IP clients, etc.

I am experiencing the exact same thing as you - My setup will work for a few days, and then all of a sudden the internet goes dead. Local network is working fine, as my NAS stays active, etc.

Its ironic that you're describing the exact same scenario as me, and I have the same Router, just a different setup.

Can you enable SSH and then as soon as you see the issue happen obtain syslog and identify the relevant log entries?

 

[ColinTaylor]

Ah, I understand now. I presume this is a CG-NAT thing along the lines that it cycles the public IP and all the local IPs associated with that public IP every 48 hours?

You're not getting a CG-NAT address you're getting a private address. In practice there's no difference from your perspective as neither is public.

Do you know what the significance of the modem talking about blocking port scan from VPN is?

No, this is why I want to know whether the IP is changing.

On the DNS theory, could it be that when Asus router reboots it first takes on DNS from ISP and then initiates VPN session whereas with just simple WAN restart it is not taking on the DNS from ISP and so stuff fails? I am trying to understand why rebooting router works but the WAN restart process fails.

That's what I'm trying to determine.

 

[Lynx]

Anything I can try in the meantime?

Would broadcasting a DHCP release packet be helpful to see how the interface reacts?

 

[marcox]

In my opinion all the problems comes from ISP and his server settings. I have the 4G-AC86U with the LTE modem inside and have same problem with lost connection and no auto reconnect.

So my ISP disconnect after 24 hours and the ausus router not check this in short time. So i have this after 24 hours and i start a cronjob now to restart wan on 4am - and now all is o.k. The schedule reboot from 86U not works with stock firmware at this time i think - and only restart wan is neccessary to fix this ISP disconnet problem.

For all others have this problem more as one time on day.... need a better script u found on this board, too. But it is a ISP thing and a problem the router have no trigger to check and fix this automatically!

 

[Lynx]

You're not getting a CG-NAT address you're getting a private address. In practice there's no difference from your perspective as neither is public.

No, this is why I want to know whether the IP is changing.

That's what I'm trying to determine.

Really appreciate your help here since I am really struggling. It happened again tonight - I lost connectivity. I had to manually stop and start WAN again to get things to work. I think this has something to do with my router working with a stale WAN IP assigned by my ISP, right? In any case, how do I prevent this from happening?

Syslog is here (think connection loss is around 23:06):

Aug 7 14:24:39 kernel: CONSOLE: 087101.195 wl1: random key value: 4A4520264E8C7 - Pastebin.com

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

pastebin.com

 

[ColinTaylor]

The problem seems to have occurred at 23:04. There's no other useful information in the log, like you restarting the connection, what the previous public IP address was, what the current public IP address is, the lease duration on the modem, contents of the modem log, etc.

 

[Lynx]

This syslog covers restart:

Aug 7 23:07:05 dnsmasq-dhcp[28213]: DHCPDISCOVER(br0) e0:98:06:9f:c5:0c Aug - Pastebin.com

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

pastebin.com

Modem log here:

2021-08-08 00:32:45UserNoticeUser admin login from 10.4.131.245 successfully - Pastebin.com

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

pastebin.com

So modem reconnects owing to 48 hour ISP refresh and my Asus router doesn't properly pick up new IP?

In any case this is bad. Router should really not just crap out like this and require manual WAN restart, right?

Maybe I need to set WAN DHCP mode continuous? Not sure what else to try.

 

[ColinTaylor]

So modem reconnects owing to 48 hour ISP refresh and my Asus router doesn't properly pick up new IP?

That would seem to be the case.

In any case this is bad. Router should really not just crap out like this and require manual WAN restart, right?

If the modem changes its interface address it should signal that to the router. It doesn't appear to be doing that so the router is completely unaware this has happened. I would blame the modem here not the router.

Maybe I need to set WAN DHCP mode continuous? Not sure what else to try.

If you haven't done so already you could try enabling the Network Monitor (Administration > System > Network Monitoring).

 

[Lynx]

Thanks for suggestion about network monitoring. What does network monitoring do? Would that force IP update or is the technical term renewal (?) after disconnect? Would that trigger WAN restart. Or would I have to set failover to secondary WAN and failback to primary WAN? The latter would feel like a bit of a kludge like restarting router every 12 hours.

Since the modem disconnects, wouldn't the ASUS router know that the WAN is disconnected for a brief period and then because of that renew IP? I mean shouldn't mere disconnect and reconnect prompt IP update? Would ISP certainly send signal in this case that the modem is not passing on?

I must admit I don't really understand how the IP renewal process works or this 48 hour refresh.

So manually switching WAN off and on appears to trigger update whereas the router seeing the WAN disconnect and reconnect does not.

Would DHCP continuous force an update in this situation? Looks rather relevant given this:

[Wireless Router] What is DHCP continuous mode? When should I use it? | Official Support | ASUS Global

Speculating here but that talks about 12 Hz refresh. Is the issue that the refresh frequency has to be high enough to detect a change in condition like the form of short disconnect seen in my case?

And other posts I have seen about problems like this.

From some searching I think I'm not the only one that has problems with WAN crapping out to do with WAN IP not being updated properly leading to loss of internet connectivity until manual intervention.

So I take your point about the possibility of the modem not passing on a signal but I am still wondering if this could be a problem with the ASUS router given all the other comments about this kind of issue.

 

[ColinTaylor]

I have no idea how the Network Monitoring would work in your situation.

I doubt that changing the DHCP mode will make any difference as that is only applicable when acquiring or renewing a lease. What is the router's WAN lease duration being set to?

Even though the modem log file indicates that the modem's WAN interface has bounced there's nothing indicating that its LAN interface (i.e. the connection to the router) has changed state.

 

[Lynx]

I have no idea how the Network Monitoring would work in your situation.

I doubt that changing the DHCP mode will make any difference as that is only applicable when acquiring or renewing a lease. What is the router's WAN lease duration being set to?

Even though the modem log file indicates that the modem's WAN interface has bounced there's nothing indicating that its LAN interface (i.e. the connection to the router) has changed state.

I really appreciate your input as I don't know what to do or try here now.
Ah good point about modem log vs what is seen by router. I guess your thinking behind network monitoring is that ideally something would prompt router to see that connection has gone bad.
The lease that is presented is always 24 hours from whenever my router picks up WAN IP from ISP so I think there is that and then there is this 48 hour refresh - whatever that is. The 48 hour refresh seems independent from WAN IP lease.
What problem does DHCP continuous solve I wonder then that requires 12 Hz frequency?

 

[ColinTaylor]

What problem does DHCP continuous solve I wonder then that requires 12 Hz frequency?

This setting tries to fix a problem with certain ISP's when the router tries to obtain its lease. In the other two modes the router will eventually give up trying to obtain a lease. In continuous mode it will carry on trying forever until it succeeds.



There is nothing in any of your log files that would indicate this setting is connected to your problem. But if you enter the following commands you will be able to see in the syslog whenever there is udhcpc activity:

# touch /jffs/scripts/dhcpc-event
# chmod 755 /jffs/scripts/dhcpc-event
# killall -s SIGUSR1 udhcpc

Aug  8 17:40:57 custom_script: Running /jffs/scripts/dhcpc-event (args: renew)

 

[Lynx]

I see what you mean now. Thank you for the very helpful explanation and script suggestion.

If anyone else reading this thread has any suggestions about how to deal with external modem reconnection causing loss of internet connectivity until restarting WAN on router, please chime in!

 

[john9527]

This syslog covers restart:

Your syslog doesn't go back far enough.....

Modem log shows the event 8/7 at 23:01, syslog starts at 23:07