GL.iNet GL-MT6000(Flint 2) - fails to connect to the internet when the DHCP lease of the upstream modem changes

Technical Support for Routers
1

Hi everyone,

First post, but hopefully an easy to address one for someone who had a similar issue.

My stack is quite simple:

  • VDSL modem from my provider receives the RJ11 connection and is used in a bridge mode right before GL.iNet GL-MT6000 with the default setup:
    image
    image
    image690×715 49.1 KB

Until yesterday, things were running smoothly with the Flint 2 properly resolving the IP address via DHCP of the upstream modem. Until today, at which point the internet stopped working and I only realized mid-conversation with my ISP that maybe the IP address changed on the modem and Flint 2 did not refresh it automatically.

And that was it. Unplugging the cable connecting the modem and the router and then plugging it again forced the router to resolve the new, refreshed IP address and the gateway and I got back my internet connection.

And thus the simple question - this isn't normal, right? I am aware that the VDSL connection has dynamic public IP address and things will change from time to time, but isn't the router supposed to handle the refresh automatically?

2

Can you set the modem into modem-only mode? So it won't connect itself?
That's the best way since you can use PPPoE on the Flint2 then.

1 Like
3

If the VDSL PPPoE in the modem, the public IP changes only for the modem interface (pppoe-wan), the IP from Modem LAN -> Flint2 WAN is supposed to be a private IP.

May I know if the PC directly connect to the modem, the Ethernet adapter of PC works well?

Please immediately export the syslogs if the WAN of the Flint disconnect to the Internet again, and PM me.

4

Thank you for all the help :slight_smile:

Can you set the modem into modem-only mode? So it won't connect itself?
That's the best way since you can use PPPoE on the Flint2 then.

This would be ideal, but I'm afraid my ISP might be a problem here (I will check that path though). The "modem/router" device is the sagemcom cs 50001 which is managed via their website. The only option I have there is to either use the device as its own WiFi router, or to switch to a bridge mode to one other specific device by providing that device's MAC address (Flint 2 mac address in this case).

If the VDSL PPPoE in the modem, the public IP changes only for the modem interface (pppoe-wan), the IP from Modem LAN -> Flint2 WAN is supposed to be a private IP.

This must be due to it being a modem/router device then, because the IP address that I see here in the Flint 2 settings is the public address of the modem (verified by going to any of the "what is my public IP address" websites):
image

The IP is also clearly different than the previous one (I have the previous one recorded)

May I know if the PC directly connect to the modem, the Ethernet adapter of PC works well?

It will take me a moment to test it with the cable (freshly moved the apartments and I am forced to use the WiFi for now), but to already provide a bit more info -> the "modem/router sagemcom device" can have its WiFi individually enabled via the ISP website while Flint 2 is working in bridge mode, and I think it can then work in parallel to the WiFi signal from Flint 2.

Please immediately export the syslogs if the WAN of the Flint disconnect to the Internet again, and PM me.

I will keep an eye on it. Given that it only happened after 10 days of running fine, it might take a while to get this to reproduce. But to give some context already, I woke up to the syslog spammed with messages like this one:

Fri Aug  9 10:12:27 2024 user.notice AdGuardHome[13123]: 2024/08/09 08:12:27.119275 [error] dnsproxy: upstream 8.8.8.8:53 failed to exchange ;shavar.services.mozilla.com.	IN	 A in 64.761µs: dialing 8.8.8.8:53 over udp: dial udp 8.8.8.8:53: connect: network is unreachable

If you think it is useful, I could send the logs of what happened after I unplugged and plugged the cable connecting it to the modem and how it renegotiated the IP addresses afterwards.

5

will be help if surely the connection is lost. Does it appear frequently?

1 Like
6

It only happened once so far. My public IP ended up changing from 91.x.x.x to 81.x.x.x, but the router did not renegotiate the new IP address until I disconnected and reconnected the cable (a reboot would do the same, I suppose).

I assume that if all else fails (like me trying to get my ISP to give me the PPPoE credentials), then a workaround could be a simple cron job script that fetches the new IP when the connection drop is detected? (I'm new to this router, so I'm not sure I would be able to make this myself though).

For now, I increased my log size in the hope that when it happens again, I will have more logs than just the last 2 hours.

7

As you mentioned, your ISP modem/router has handled the modem/PPPoE, so the public IP is in the modem WAN, not in the Flint 2, the Flint 2 only get the private IP from the ISP modem/router.

(RJ11) -> ISP modem/router (PPPoE) -> (LAN -> WAN) -> Flint 2

When the ISP modem/router refresh the public IP from the ISP, it supposed not affect the Flint 2, since the IP of the Flint 2 is private, and it provided from the ISP modem/router, probably supposed to be checked the ISP modem/router with ISP.