Packet loss due to OpenWrt and the modem/router battling for the same IP addres (was: Packages drop on TP-Link Archer C60 19.07)

I recently installed OpenWRT 19.07.3 on my TP-Link Archer C60 v1, but ever since I did so, I started running into trouble with packages dropping like crazy – we’re talking in the 70-80% range of packet loss. When the packages do get through, it’s quite speedy though.

I can replicate this problem both on WiFi (both on 2.4 and 5 GHz) and cable. I can even replicate this problem pinging from the router itself.

If I use the same cable and port that goes from the modem into the router and connect it directly into a laptop, there is no packet loss, so I assume the problem is not in the cable or the modem either.

Any help would be greatly appreciated, as this is affecting me quite a bit.

System log: https://pastebin.com/5ZeG8Ua

Kernel log: https://pastebin.com/T35TgZXX

The following issues seem to me like they might be related, but then again, I’m not a network engineer by any stretch of imagination:

https://bugs.openwrt.org/index.php?do=details&task_id=2216
https://bugs.openwrt.org/index.php?do=details&task_id=2730


False alarm. It turned out the TP-Link was battling for the same IP as the telco’s modem/router (i.e. WAN from the OpenWrt PoV).

I’m closing this thread and will rename it accordingly.

Massive thanks go to the #openwrt IRC channel, especially PaulFertser there, for walking me through this issue.

As a side-note, it might be cool if LuCI would warn when issues like this show up.

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  • Why did your upstream device issue the same IP to two different devices? (some ISP devices only provisioned for one IP could function like this :wink: )
  • @hnyman ...are there any log messages for conflict IPs?

From what I can tell, this is what happened:

  • telco’s modem/router was (by default) set to have its IP as 192.168.1.1
  • OpenWrt router was (by default) set to have its IP as 192.168.1.1
  • telco’s modem/router issued the OpenWrt router the IP 192.168.1.2

As a result, it seems that when I connected to the OpenWrt router, it thought it’s IP is 192.168.1.1, but when the packet got from the OpenWrt router to the modem/router that box thought it’s IP was 192.168.1.1.

It sounds like your OpenWrt LAN and WAN are both improperly numbered 192.168.1.0/24. Traffic won't pass since the router thinks it's the same network.

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Yes, that was the problem. I managed to fix it by simply changing the LAN on OpenWrt to 192.168.0.1/24. I apologise, that I forgot to mention that in my first reply.

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