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OpenVPN Site to site on 2xASUS RT-AC86U Routers. Slow speed down, fast up.

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Peter Olsen

Occasional Visitor
Hello.

I have two Asus RT-AC86U one at my home and one at my parents house. Both on Merlin Firmware Version: 386.7_2
Its been a while since i speed tested, but i used to get 200 Mbps both up and down when transferring files to and from my parents house.

I have not done any configuring since last speed test, but now i suddenly get 30-40 Mbps download when at my parents house. Upload speeds are fine at around 200Mbps.
Last time i speed tested, (many months ago) i got 150-200 both ways. Ping is stable at 6ms.

Link at home: Fibre 250 Mbps both up and down, same at my parents house, speed testing confirms speeds are fine outside of vpn.

OVPN Server at my house setup:

routersetup.png




I have tried setting from tcp to udp, and tun to tap, no difference.
Tested with openvpn client directly on pc, no difference.
Power cycled both routers, no difference.
Tried with asus official firmware, no difference.
The CPU on the router with ovpn server is always well below 20% when downloading (Windows smb share) and a bit higher when uploading. No worrying cpu spikes on the client side either.


Any help with this matter would be greatly appreciated
The weird thing i have not done anything to the config of ovpn, neither on client or server side.
All i have done since last speed tests is updated the firmware, not sure how many times, but at least 4-6 updates, maybe more.
 
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Try disabling compression. It's not needed in most cases and speeds things up.
 
Still the same results unfortunately:

Download speed:

down.png


Upload speed:
up.png



I have tried with different files, and from/to different Windows machines and NAS server.
On the internal network speeds are fine.

Something very spooky going on :eek:
Maybe i have to buy new routers.
The only things i have not tried is to factory reset my routers or downgrade the firmware to a much older version, but im not sure if there would be any point to that, neither would it feel secure to run on a very old firmware.

Edit: I tried to create a new vpn server and client with default settings (UDP), same down speed but half the upload speed (13MB/s).
 
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I see some people complain on vpn speeds on the rt-ac86u after fw versions 384.19.
Could this maybe be the case for me as well?
 
FWIW but don't want to hijack your thread: I too just observed unexpected assymetrical download speeds with two Asus routers using VPN Server and VPN Client. Both ends had internet upload speeds of 35-40Mbps and >10x download speeds (speedtest.net without VPN). One direction got network-network downloads of 20Mbps and the other direction 3Mbps (iPerf3 with VPN). With a MacBook using MacOS VPN Client to Asus (AX86U) VPN Server I got symmetrical downloads of 20Mbps. I think this is different to your situation. I was at a temporary house rental so didn't spend time trying to debug and didn't post here. If this happens again I will dig in more.

UPDATE 10/22: had a second chance to try check this at a different location. My AC66U-B1 router w/OVPN client (now Merlin 386.7_2) was connected through LAN cable to a TP-Link Archer 7 (AC1750) router to Spectrum modem. Unfortunately after a minute or so the TP-Link router would crash and disconnect its WiFi clients such as the landlord's Ring doorcam and door locks :). Rebooting everything and repeating would see the same TP-Link crash problem, so I had to disconnect the AC66U-B1 and give up testing. Don't buy a TP-Link router.
 
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Still the same results unfortunately:

Download speed:

View attachment 44707

Upload speed:
View attachment 44708


I have tried with different files, and from/to different Windows machines and NAS server.
On the internal network speeds are fine.

Something very spooky going on :eek:
Maybe i have to buy new routers.
The only things i have not tried is to factory reset my routers or downgrade the firmware to a much older version, but im not sure if there would be any point to that, neither would it feel secure to run on a very old firmware.

Edit: I tried to create a new vpn server and client with default settings (UDP), same down speed but half the upload speed (13MB/s).
Are you transferring files that are directly saved to the device they are being transferred from, or are you transferring from a USB storage of some kind that happens to be connected to that device? This may also play a factor on the observable transfer speeds since the transferring storage may be the bottleneck to the connection.
 
Are you transferring files that are directly saved to the device they are being transferred from, or are you transferring from a USB storage of some kind that happens to be connected to that device? This may also play a factor on the observable transfer speeds since the transferring storage may be the bottleneck to the connection.

Directly from sata NAS harddrives to pc sata ssd.
No usb. They do around 100MB/s on the local network.
 
I see some people complain on vpn speeds on the rt-ac86u after fw versions 384.19.
Could this maybe be the case for me as well?

If i get some time this week i will try to downgrade and see what speeds i get, but not easy when i am working from home, and every other family member is always doing something online :cool:
 
If i get some time this week i will try to downgrade and see what speeds i get, but not easy when i am working from home, and every other family member is always doing something online :cool:
You should try doing some simple local file transfers between devices locally on your network to see if the issue resides there as well.(before doing the downgrade) also consider doing the same on the other routers network. (I am making the suggestions to see if you can narrow down if both router sides are experiencing the same problem together through openvpn, or is something going on somewhere down the line creating the bottleneck).
Basically, do some other forms of tests. Some factors to consider, are either transferring devices hardwired connected, or are they connected over wifi. Another factor to consider is what version of Samba sharing (or file sharing) does the network on both ends use. Is there maybe some outdated settings being used that needs to be adjusted on either routers (or devices)?
 
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You should try doing some simple local file transfers between devices locally on your network to see if the issue resides there as well.(before doing the downgrade) also consider doing the same on the other routers network. (I am making the suggestions to see if you can narrow down if both router sides are experiencing the same problem together through openvpn, or is something going on somewhere down the line creating the bottleneck).
Basically, do some other forms of tests. Some factors to consider, are either transferring devices hardwired connected, or are they connected over wifi. Another factor to consider is what version of Samba sharing (or file sharing) does the network on both ends use. Is there maybe some outdated settings being used that needs to be adjusted on either routers (or devices)?
Thanks.

No issues on local network or with internet speed. (Internet 250 Mbps down/up with speedtest, on both locations)
I dont think smb is the issue, both machines i usually try uses win11, i also tried from NAS to win11, same results.

1665406328776.png
 
Thanks.

No issues on local network or with internet speed. (Internet 250 Mbps down/up with speedtest, on both locations)
I dont think smb is the issue, both machines i usually try uses win11, i also tried from NAS to win11, same results.

View attachment 44724
I am curious why openvpn is giving you this issue. It seems like something that needs to be fixed. I wonder if it is bypassing any hardware acceleration.
 
I think i have some time tomorrow, will try a factory reset first, then downgrade if that does not help.
Keep it bare minimum by not enabling a bunch of other features right after the reset. Start with the bare minimum to use the vpn. If it fixes it, then slowly add things back while periodically checking if something breaks it again.
 
So, a factory reset fixed the issue. Latest Merlin firmware working fine.
250Mbps Down / 150Mbps UP

Thanks for all the suggestions along the way :)

Edit:
I re uploaded my old config, and the speeds still seemed good.
Just in case, i will set everything up from scratch, should not take more than 20 minutes.
 
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