@tp_user 

Hello, sorry to hear that.

May I know is there any QoS setting in the configuration? It is suggested to reset the whole settings to factory defaults and set it up again but not import the backup file. 

Please also check how did you test this speed and is there any specific operation that may cause this speed drop? What if you disconnect the Synology NAS and only leave the PC connected, then check the wired speed again? Can I have the model number of the Synology NAS?

Thanks.

Kevin_Z wrote

May I know is there any QoS setting in the configuration?

Shouldn't be, I haven't installed/used the Tether app. Can't configure it through the webui.

Kevin_Z wrote

It is suggested to reset the whole settings to factory defaults and set it up again but not import the backup file.

I took it out of the box, updated the firmware and reset it. After that:

1. Change LAN to 172.16.16.1 - 255.255.255.0
2. Disabled everything under IPTV (TV is directly connected to coax)
3. Added 8 DHCP address reservations
4. Fixed the wireless channels because of channel pollution from neighbours (prevent bad reception in different room)
5. Enabled access control and added two (camera) devices to the blacklist but haven't connected them to the network yet
6. Disabled all ALG passthrough options except voor L2TP and IPSec
7. NAS in DMZ (has it's own firewall)

So that's what I did two days before the issue started to occur for the first time. Will try it again, but I don't see why it would fix it permanently the second time on the same firmware version.

Kevin_Z wrote

Please also check how did you test this speed and is there any specific operation that may cause this speed drop?

Speedtest.net (got the history of the results as well) and double checked with the speedtest supplied by my ISP. The results were always within range of error.

No special cause, one moment I'm browsing youtube on my wired PC and the next moment the video's dont buffer because my speed dropped to 0.38 Mbps (this happened yesterday). Verified the same congested speed wireless on my phone. The buildin traffic monitor also didn't show any high activity. Also zero system logs.

Rebooting devices (PC, Modem, Router) didn't fix it. Factory resetting the router and restoring did, as explained in the start post.

Kevin_Z wrote

What if you disconnect the Synology NAS and only leave the PC connected, then check the wired speed again?

I think I have tried this already and it didn't change anything. But I will verify again the next time it happens.

Kevin_Z wrote

Can I have the model number of the Synology NAS?

DS713+, single connection, haven't enabled link aggregation.

@tp_user 

Thanks a lot for all the details.

Please try my previous suggestions and monitor the result. Let me know if there is any difference.

@Kevin_Z 

It took exactly one month for the issue to resurface. This is a couple of days after updating from 1.0.8 to the newer 1.0.9 firmware build. Related? I can't tell.

While gathering the facts and disconnecting all of the connected (wireless and wired) devices except my desktop, the issue remained. But this time I didn't only look at the advanced interface tab. Apparently the basic interface tab somehow shows more details, because it tells me that internet port negotiated 100Mbps instead of 1000Mbps (see screenshot).

And there's the reason for the sudden speed drop from 250 to 85Mbps. But why does this model do this? Again, I never seen this issue with my previous router.

//edit:

I've just now noticed the existence of the "Internet Port Negotiation Speed Setting" option which is set to "Auto negotiate". Setting this to "1000Mbps Full Duplex" immediately restored my speed. Let's hope this is a permanent solution, but if it is, I don't think this should be considered normal behavior.

@tp_user 

Hello, thanks for the update.

Please monitor the performance again and we will also test this on our side and update.

Good day.