Linksys MR7500 boot loops when ethernet is plugged in

Installing and Using OpenWrt
1

I recently bought a used Linksys MR7500 and installed OpenWRT on it. I followed the instructions here in order to get it installed on both partitions. I am currently running into an issue where the router bootloops if any ethernet cables are present during boot. I can only access it by letting it boot with nothing plugged in, waiting a few minutes, and then plugging in a cable. I believe 25.12.0 is installed on one partition, and 25.12.4 on the other (the web UI doesn't seem to be able to update both). The only config changes I've made were to enable wireless, and set one LAN port to act as WAN. The real WAN port not working seems to be a known issue for this device.

My network config is as follows:

config interface 'loopback'
        option device 'lo'
        option proto 'static'
        list ipaddr '127.0.0.1/8'

config globals 'globals'
        option dhcp_default_duid '00042db3812b4d68462d85075bc909dc4bee'
        option ula_prefix 'fdf3:3f10:da9b::/48'

config device
        option name 'br-lan'
        option type 'bridge'
        list ports 'lan1'
        list ports 'lan2'
        list ports 'lan3'

config interface 'lan'
        option device 'br-lan'
        option proto 'static'
        list ipaddr '192.168.1.1/24'
        option ip6assign '60'

config interface 'wan'
        option device 'lan4'
        option proto 'dhcp'

config interface 'wan6'
        option device 'lan4'
        option proto 'dhcpv6'

I also tried to include a boot log, but it didn't fit within the max post size. This is my first time using openwrt, so sorry in advance if this is a rookie mistake.

2

Could the default IP address be conflicting with some other device in your network?

3

I don't think so. I've been able to reproduce the issue by plugging a single device (my desktop) into the router. The bootloop happened regardless of whether I set my desktop to use a static ip (192.168.1.2) or dhcp. If I plug it in after boot, the desktop successfully picks up an address from dhcp.

4

I could imagine a scenario where the inrush current requirements at boot time are causing a brownout and thus resulting the boot loop. Although it shouldn't be a huge difference, the ethernet connection may increase the power to the point where it browns out.

A quick search suggests that the MR7500 requires a 12V 3A (36W) power adapter. Is this consistent with what you are using? And do you happen to have another 12V 3A adapter you could use as a test (in case your adapter is faulty)?

5

I did actually manage to find another 12v 3A power supply, and am seeing the same behavior. I also have a friend who bought another used MR7500 at the same time as me, and is now running into the same issue. I believe this issue on github could also be related.

Another interesting thing I noticed is that the port in use seems to have an effect. Sometimes switching the desktop to a different lan port makes it suddenly stop looping. So far it seems lan1 causes the issue most consistently, while lan3 frequently works.

6

I have had a bit more time to experiment, and I've tried the following with no success.

  • Setting a static IP on my desktop
  • Disabling DHCP entirely on the router
  • Changing the router's IP range to 192.168.2.1/24
  • Running firstboot and starting fresh
  • Using ethtool to limit a lan port to 100mbps

Unfortunately, none of those seemed to have an effect. I do own a USB-to-Serial adapter, so I am considering trying to capture a log of the failed boot. Is that the best path forward?

7

The instructions you have linked to are for MR7350... Could this have something to do with your problem?

8

It could, but that is a very similar router with a similar CPU. Yesterday I used the same procedure to flash dd-wrt, and that doesn't seem to suffer from the bootlooping issue. It also fixed my WAN port.