Hi @David-TP , thanks for the reply.

"Have you noticed any performance issues when the packets dropped a lot on the first hop, such as slow loading when accessing the NAS server or something else?"

Yes, I have been having intermittent network issues which I am trying to track down.

The most recent symptom was terrible performance on my AppleTV (lots of pauses for buffering). The AppleTV is only 10' from the main Deco M5. I tried putting it in priority mode, and turned off mesh to make sure it only accessed the main deco. At the same time, I also checked the MTR on my laptop - no dropped packets observed internal to the network, but for some reason routing to the DNS server was not working (even using the IP address directly). The DNS servers were fine when accessed directly from my DSL router. I rebooted the Deco routers yet again, which fixed the DNS problem, but I still had poor performance on the AppleTV. I switched the AppleTV to the WIFI net controlled by the DSL router - and it then ran flawlessly.
 

"And are you able to reproduce this packet loss most of the time? or How many times have you noticed this issue already?"

The problem with intermittent network problems. I was seeing the dropped packet issue consistently yesterday, but today the mtr looks fine (except for the afforementioned loss of routing to the DNS servers). But, still poor performance on the AppleTV.

"If possible, have you ever tried to set Deco into Access Point to see whether the same packet loss continued:

How to set up Deco to work in Access Point mode"

[EDIT] 
I have not. I'm not sure what the benefit would be (unless it fixes some inexplicable issue, but that's not really how I like to debug things). I assume I would also have to go and reconfigure every WIFI device in my network (I have about 20 Wifi clients in the house), so probably not a 2 minute experiment.

 Part of the beauty for me of a mesh network is being to set up something completely separate to the DSL router network. I can't see any theoretical reason why my setup shouldn't be rock solid, so I don't particular want to change it unless there is a good reason (I mean, an actual technical reason why AP mode would be more robust that router mode).

OK, I was perhaps getting confused about AP mode. I think there was a mode where you needed to port all of the IP settings from the main router, but AP modes looks to be pretty much plug and play. I'll give it a try...



Regards,

               Chris.

ps - I also learned a little more about ICMP filtering - which may be part of the reason I was seeing the dropped packets with multiple MTRs running in parallel. I am changing my debug technique to only run a single MTR command at a time, to take that out of the equation.