RT-AC86U Asuswrt-Merlin OpenVPN torrent makes internet crash

[Begreen]

I need some help with a quite annoying problem I have using VPN on my Merlin flashed router.
When I start torrenting over VPN, my whole internet connection crashes (not just the VPN tunnel) and my modem needs to recycle and re-acquire an IP from my ISP every couple of minutes. The crash varies in frequency between 5 and 10 minutes without any pattern. This only happens when torrenting, normal internet traffic through the VPN can go for days without interruption.

My setup:
ISP > own modem in Bridge mode > RT-AC86U Merlin (384.6) > home network

I'm in Australia where internet is still pre-historic with a PPPoe ADSL2+ connection and I achieve max speeds of 1.4Mbs, so the router cannot be overloaded.
My home network consists of 2 laptops, Apple TV, HomePod and a Synology NAS. This should also be more than ok for the router to handle.

The problem occurs both when torrenting on the NAS and from laptop (with NAS disonnected from network).

What I already tested:
- used another modem -> same problem
- changed VPN provider (Expressvpn & VPNarea) -> same problem
- activated VPN tunnel directly on NAS instead of router -> same problem
- ISP checked the line, noise, node -> no change
- original ASUS firmware on router -> same problem

The only setup were I have no crash of internet is having VPN on my laptop and torrenting from my latpop with utorrent. When I use Transmission, the connection also crashes.

It's driving me nuts. What can be the cause?
Thanks for your help guys (&gals)!

 

[Grisu]

you could try your provider modem in router mode (without 86U) on laptop to see if it will work correctly.
Then use your 86U in router mode (double-NAT) too, test on laptop and on router.
Just to see the differences and get a better sight what is causing your issue.

 

[Jack Yaz]

How many connections are you allowing the torrent clients to make when connecting to peers?

 

[Begreen]

you could try your provider modem in router mode (without 86U) on laptop to see if it will work correctly.
Then use your 86U in router mode (double-NAT) too, test on laptop and on router.
Just to see the differences and get a better sight what is causing your issue.

Completely disabled 86U from network and used modem as router:
VPN on laptop + torrent: worked for 1h straight, no disconnect
VPN on Synology + DL Station: worked for 1h straight, no disconnect

86U in router mode:
VPN on laptop + torrent: connection crash
VPN on Synology + DL Station: connection crash
VPN on router + DL Station: connection crash
VPN on router + torrent on laptop: connection crash

Conclusion: it doesn't happen when the router is out of the network.
When disconnect occurs, this is the router's log:
Sep 20 12:58:32 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link DOWN.
Sep 20 12:58:34 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link UP 100 mbps full duplex
Sep 20 12:58:46 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link DOWN.
Sep 20 12:58:49 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link UP 100 mbps full duplex
Sep 20 13:00:30 ovpn-client1[9294]: [VPNArea] Inactivity timeout (--ping-restart), restarting
...
Sep 20 13:00:58 WAN_Connection: ISP's DHCP did not function properly.
Sep 20 13:00:58 DualWAN: skip single wan wan_led_control - WANRED off
Sep 20 13:00:58 nat: apply redirect rules
Sep 20 13:01:01 rc_service: udhcpc 9652:notify_rc start_firewall
Sep 20 13:01:01 wan: finish adding multi routes
Sep 20 13:01:01 nat: apply nat rules (/tmp/nat_rules_eth0_eth0)
Sep 20 13:01:01 rc_service: udhcpc 9652:notify_rc stop_vpnclient1
Sep 20 13:01:01 rc_service: waitting "start_firewall" via udhcpc ...
Sep 20 13:01:02 ovpn-client1[9294]: event_wait : Interrupted system call (code=4)
Sep 20 13:01:02 ovpn-client1[9294]: vpnrouting.sh tun11 1500 1621 10.186.34.22 10.186.34.21 init
Sep 20 13:01:02 openvpn-routing: Configuring policy rules for client 1
Sep 20 13:01:02 openvpn-routing: Tunnel down - VPN client access blocked
...
Sep 20 13:01:04 WAN_Connection: WAN was restored.

Remarks:
1. First log entry when connection crashes: kernel: eth0 on Port 3 DOWN
-> there's nothing connected to Port 3
2. OpenVPN client is set to: "Automatic start at boot time - NO"
-> the VPN connection is OFF after the crash and recycling, but the router hasn't rebooted
3. Modem doesn't seem to flinch, just says connection lost, then reconnects

 

[Begreen]

How many connections are you allowing the torrent clients to make when connecting to peers?

Clients have initial configuration. Some have 200 connections, other 100 connections.
I lowered this to 10: no change.

 

[Grisu]

When disconnect occurs, this is the router's log:
Sep 20 12:58:32 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link DOWN.
Sep 20 12:58:34 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link UP 100 mbps full duplex
Sep 20 12:58:46 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link DOWN.
Sep 20 12:58:49 kernel: eth0 (Int switch port: 3) (Logical Port: 3) Link UP 100 mbps full duplex

for me it looks like ethernet problem on eth0.
Either cable or port itself on router or modem.
Thats why you see link down, setup with 100Mb/s (should even be 1Gb/s if supported by modem).

 

[Begreen]

for me it looks like ethernet problem on eth0.
Either cable or port itself on router or modem.
Thats why you see link down, setup with 100Mb/s (should even be 1Gb/s if supported by modem).

Speed at 100Mb/s is normal as it's an ADSL modem.

After some research, eth0 seems to be the internal assigned port for the WAN connection (ie PPPoe modem).
Tried with different cable: same problem
Different cable + different modem: same problem

Also, this really only happens when torrenting. My connection + VPN have been up for 3 days now with normal internet traffic without any interruption. Once I start a torrent, internet crashes every 5-6 minutes.

Also it is just the combination of torrent + VPN (independently on which device the VPN is activated - router, NAS or laptop) that triggers the internet to crash. When I launch a torrent on open connection without VPN, internet doesn't crash.

 

[DDR]

I had a similar issue that drove me crazy for a month or so (RT-AC68U/ADSL bridge/PPPoe/ssl vpn etc.).
I finally just restored a backup config and it all went away.

 

[Begreen]

Just an update on this problem: I throttled the max speed of my downloads, limiting it at 1.1 Mb/s. Since I've done that, my internet doesn't crash anymore.

I changed everything in my setup (including cables, router, laptop, really everything) and the problem still happens. I spent hours on the phone with ISP's helpdesk, claiming the problem was on my side.
At some point I noticed it happened when my download speed hit the max DL rate I usually measured on my line. So I tried with throttling my max DL speed so it couldn't reach my max line speed. And I'm (slightly) happy to report that since I did that, my internet connection doesn't crash. It's been up 4 days now without a glitch while torrenting over VPN.