Random connection lost from OpenWrt router to main router

I stumbled upon an awkward situation that I've never encountered in more than a decade using computer. That is, a random connection lost from a secondary router to the primary router, both inside my home.

Random request timeout when pinging an Internet server is very common, but how can it happen when my PC ( connects to the OpenWrt router ( for LAN and 192.168.1.x for WAN) using a 50cm cable, and the OpenWrt router itself connects to the main router ( just 30m away using cable as well?

The random drops are annoying, even when surfing the web. Online gaming is out of the question. Everything works normally if I connect my PC directly to the main router using the 30m cable mention above. The presence of the OpenWrt router is just for testing purpose -- I want to play around with it before using it as the main router.

My OpenWrt router is a Newifi D2 which is pretty powerful, while the concurrent home users are 5-7 at worst. They all connect directly to the main router, except my PC which is behind this secondary one. I know this problem is hard to diagnose. But what could be the cause of it? Can you guys suggest some common possibilities?

I'd check the syslogs and kernel logs from the router's side.

Have you properly configured the routing (as dumb AP, only LAN ports in use, WAN unused), as you seem to have the same subnet on the main router and in the secondary OpenWrt router? And have the gateway, DNS etc. defined right.

If you are trying to the WAN port on the OpenWrt router in a use double-NAT fashion, you need a different subnet on the OpenWrt LAN side than its WAN side.

So, first guess is routing problem. But that could be wrong guess if you have a dumb-AP config without routing.

you might describe your routing topology a bit...

It is a simple double NAT, with the OpenWrt connects to the main ISP router via a cable from ISP router's LAN port to OpenWrt's WAN port. For WAN side, it has 192.168.1.x allocated by DHCP. For LAN side, it has the address of

Ok, that double NAT sounds ok.

Other observation is that your ping "from PC to ISP router" does not actually tell clearly on which cable the connection breaks: between PC and OpenWrt, or between OpenWrt and ISP router.

You should ping from PC both the OpenWrt router and and ISP router (and possibly from OpenWrt SSH console ping the ISP router).

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Thanks a lot. The culprit turned out to be the 50cm cable from my PC to the OpenWrt router. Pinging from OpenWrt (using SSH) to the main router is never timed out, while pinging from my PC to OpenWrt and to the main router does.

The broken cable caused the Ethernet interface on my PC change states from Connected to Disconnected and Identifying... quite often. That's when the packet loss happens. I never think of such situation, and always assume that once connected, it will work.

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