GT-AX6000 WAN Disconnections - 'ISP DHCP Not Functioning Properly'

[cypr919]

Greetings,

I recently purchased this router and initially had no issues. However, for about a week now, I have been experiencing multiple disconnections per day, accompanied by a generic 'ISP DHCP not functioning properly' message.

Furthermore, I am using a 5G modem (ZTE MC889) with an Asus router connected behind it. Initially, I had the 5G modem in bridge mode, and the Asus router obtained its IP directly from the ISP. I thought the WAN lease might be expiring, so I turned off the bridge mode setting on the 5G modem and placed the Asus router behind NAT in DMZ. However, the internet dropouts continued at the same if not higher frequency, which is driving me crazy.

I want to mention that the 5G modem itself is rock solid with zero service interruptions.

I will attach two log files: one from when the Asus router was connected to the 5G modem in bridge mode and another when it was behind NAT. Additionally, in the 'syslog_bridged' file, I had this script enabled at the time: https://github.com/lynxthecat/maintain-wan-lease.

Finally, I am using Merlin's firmware with version 3004.388.4_0_rog. I hope someone can help me with this issue because I have been searching nonstop for a solution for the last 4-5 days.

 

[ColinTaylor]

I suggest that you switch to using the router's 1GbE WAN port instead of the 2.5GbE port. I'd also suggest that you disable IPv6 on the router to simplify troubleshooting. See if those changes make any difference.

Does the ZTE have any log files?

 

[cypr919]

Hey, thanks for your reply. I tried using the 1GbE port as the primary WAN (dual WAN setting), but the issue remained. Furthermore, I experimented with all three DHCP query frequency options: aggressive, normal, and continuous. Additionally, I disabled IPV6.

As for the logs from the ZTE device, I reviewed them and didn't notice any service interruptions or IP address renewals. Unfortunately, I had deleted the logs I had saved, and I reset the device afterward. I will post the logs from the ZTE device when the issue reoccurs.

*Edit: I should also mention that when the Asus router starts acting up, if I disconnect the WAN cable and connect it directly to my PC (ZTE -> desktop), the connection is restored instantly, even in bridge mode.

 

[Crimliar]

Probably not going to help much:
The GT-AX6000 only has a single WAN port - capable of up to 2.5Gbps.
The connection is CGNAT, and it looks like it's refreshing the connection very often. You could try setting Administration > System > Auto Logout to "0".
As it's a CGNAT connection you may as well turn off uPnP!

 

[cypr919]

The issue occurred minutes ago. Please find attached the logs from the ZTE device and the Asus router. The timestamp should be around 2023-10-24 21:25:25, and from the ZTE device I notice the following status '[system][notice]Lan eth0 pulling out '.

 

[cypr919]

Probably not going to help much:
The GT-AX6000 only has a single WAN port - capable of up to 2.5Gbps.
The connection is CGNAT, and it looks like it's refreshing the connection very often. You could try setting Administration > System > Auto Logout to "0".
As it's a CGNAT connection you may as well turn off uPnP!

I will try setting auto logout to 0 now. Also the CGNAT IP has remained the same for days now.

 

[ColinTaylor]

I don't think changing the logout period for the router's web interface will have any bearing on WAN interface. When your modem was bridged you didn't have a CGNAT address, but you did have a private address (10.x.y.z), which is fairly common for a mobile connection, so the comment about UPnP is still valid.

P.S. Please don't redact private IP addresses (e.g. 10. 192.168.) from your log files, it's pointless and just makes things more difficult to diagnose.

 

[ColinTaylor]

The issue occurred minutes ago. Please find attached the logs from the ZTE device and the Asus router. The timestamp should be around 2023-10-24 21:25:25, and from the ZTE device I notice the following status '[system][notice]Lan eth0 pulling out '.

I suggest you replace the ethernet cable between the modem and the router.

 

[cypr919]

I don't think changing the logout period for the router's web interface will have any bearing on WAN interface. When your modem was bridged you didn't have a CGNAT address, but you did have a private address (10.x.y.z), which is fairly common for a mobile connection, so the comment about UPnP is still valid.

P.S. Please don't redact private IP addresses (e.g. 10. 192.168.) from your log files, it's pointless and just makes things more difficult to diagnose.

I didn't redact any IP addresses, they appear as such by default (that 10.xxx IP is the CGNAT one). Now I disable UPNP once it was mentioned and the issue remains. Moreover, replaced the cable connecting the Asus router and the 5G modem POE injector, basically the hardware setup is: ZTE MC889 ---> (cat 6 cable) ----(2.5GbE POE) ---- Asus router. If the cable from the 5G modem to the POE injector was malfunctioning, I'd imagine it would lose power/service.

 

[ColinTaylor]

All indications from your log files suggest this is a physical problem with the link between the router and the modem.

 

[cypr919]

I restarted the Asus router and on initialization I checked the logs from the ZTE, the message logged is '[system][notice]Lan eth0 pulling out '. I doubt the cable is the problem. Nevertheless, I ordered a new cable to eliminate this possibility.

 

[glens]

In summary, you've seen the same happen on two different router physical ports. Chances of them /both/ (individually) being iffy are pretty slim. That narrows it down to something they have in common either upstream or down. It may be a faulty router (manufacturing ain't usually 100.0%), but the interconnect would be both my first place to look, and the easiest / cheapest-route to eliminate something from the equation.

 

[cypr919]

Thank you all for your replies, I will report back once the new cable arrives and use it for a while.

 

[Tech9]

If you search SNB Forums you'll find this very same issue with Asus routers was reported multiple times for multiple models and ISPs. Most of the time it's some still unknown incompatibility related. Continuous Mode in WAN was added to address it, but it doesn't help always. Try with new Ethernet cables, but you may also find non-Asus router working perfectly fine with the cables you have.

 

[bbunge]

Why do you have a PoE switch between the modem and router?

 

[ColinTaylor]

Why do you have a PoE switch between the modem and router?

The ZTE MC889 is an outdoor device that's power by the supplied PoE adapter.

 

[bbunge]

The ZTE MC889 is an outdoor device that's power by the supplied PoE adapter.

OK, I did not pick up on that. Even more reason to suspect the cable/connectors. I also noted the OP is using CAT 6 cables where CAT 5e would work just fine.