Problems reaching modem

[studunihd]

Hello,

I am a long time reader and, until now, I could solve the few problems I have just by silently reading the forum. Now I am facing an odd problem I hope you can help me with. I am using a RT-AX88U (non Pro) with Merlin 3004.388.9 behind an Vodafone Station (ISP cable router) in bridge mode. Lately I have had upload problems and I needed to check the status page of my modem, which is accessible on 192.168.100.1. This works for a few minutes after rebooting the AX88U. After one to two minutes the modem is no longer reachable (connection timed out). It becomes reachable again for up to two minutes if I change anything on the LAN->Route tab in the router settings. I have tried multiple different combinations I found here and all that work share the same behaviour as having no entries at all. It stops working after a maximum of two minutes. I can see this also with a continuous ping. It works at first and then gives me time outs. I also tried sshing to the router and running "ifconfig $(nvram get wan0_ifname):0 192.168.100.2 netmask 255.255.255.0" without it changing anything. Any insight is much appreciated.

 

[ColinTaylor]

Any VPN being used?

 

[studunihd]

No clients but one OVPN and one wireguard server.

 

[studunihd]

One other thing: The modem stays reachable if it is directly connected to the computer without the AX88U.

 

[ColinTaylor]

As the modem is initially reachable (and after changes to the LAN) it does suggest some sort of routing change taking place. What do you see happening in the System Log when you loose connectivity? You might need to set "Log only messages more urgent than = all" to get more information.

 

[studunihd]

There were no messages on the standard setting and I could not see any changes in the routing table but I will try again with your log level suggestion.

 

[studunihd]

Even with the new log level there are no messages displayed. Is there a way to debug wether reguests are dropped by the router or the modem? The ISP modem is very bugy in router mode. I have not had any other problems with it in bridge mode but it would not surprise me if the problem originates from the modem. Unfortunately the modem itself does not have a usable log itself.

 

[ColinTaylor]

Given that there's no messages in the System Log I'm now inclined to think this is a modem issue, especially if you say it has a history of being buggy in router mode. Perhaps there are some other forum members with a Vodafone Station that can comment on that.

As for debugging the problem, as you are using Merlin's firmware you could install Entware and then tcpdump. Using tcpdump you could monitor what packets were going between the router and the modem.

 

[studunihd]

Thank you for your help. I may try tcpdump later as I do not use entware so far.

 

[W3Wilkes]

Were you running Merlin's 3004.388.8 prior to installing .9 and if so did it run just fine?

 

[studunihd]

Yes, have been running Merlin for years and this is the first problem that I wpuld consider a bug (not necessarily caused by Merlin). The problem also occured on 388.8 and at least one earlier revision. It might have always behaved like this. I did not need to check the modem as often before recently.

 

[aex.perez]

Thank you for your help. I may try tcpdump later as I do not use entware so far.

On the AX88u, when it's working and when its not, what does the routing table on the router look like under both scenarios, for comparison?
(available via the GUI or command line via SSH)

 

[Crimliar]

Before you do anything else, save your router settings.
Then on the main WAN settings page of the router, try:
Get the WAN IP automatically: no
IP Address: 192.168.100.10 -or- 192.168.100.2
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.100.1

In most cases, the router will still pick up the WAN-DHCP settings, but will add this as an extra route that just gets you to the modem. I've been told more than once on this forum that this shouldn't work, but I had this setup working flawlessly for several years! If it doesn't work, just restore the previous settings!