Orbi NBR750 tips for TTL and reboot loops

Post by **jericsmith** » Sun Jun 11, 2023 2:52 pm

Recently picked up an NBR750 5G and used a lot of the tips in the NBR Mega-Thread. I figured I'd share a few other things I found:

- TTL:. If you want to adjust TTL and HL on a more permanent basis as well as set values for HL, and have enabled telnet or SSH you can add the appropriate IPTables to the existing firewall configuration as follows:

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Open a shell to your NBR750 and then

# cd /etc/arno-iptables-firewall
# vi custom-rules

Now goto the last line and hit 'i' (for "insert"), start a new line and paste in:

iptables -t mangle -I POSTROUTING -j  TTL --ttl-set 65
iptables -t mangle -I PREROUTING -j TTL --ttl-set 65
ip6tables -t mangle -I POSTROUTING  -j HL --hl-set 64
ip6tables -t mangle -I PREROUTING  -j HL --hl-set 64

(Obviously change the values to what works for your carrier, this is my setup for T-Mobile.)
Then hit 'esc' to leave editing mode, then ':' and wq and enter. That should write the file and quit you back to the shell prompt.

- Boot loops on 5G: I was having an issue where if I had the wireless internet set to "Automatic" rather than "4G" the unit would successfully connect and then reboot shortly thereafter. I figured there was some sort of watchdog getting tripped erroneously. After some nosing around I found there is a special debug page for the modem and thankfully there is a setting to disable "recovery mechanism".

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In a browser, goto http://192.168.1.1/debug_lte.htm
Switch to the "Logs" tab
Disable "Recovery Mechanism" and hit apply

et voila, watchdog disabled and bootloops gone.

This is also a useful page to monitor some of the logs related to modem to do troubleshooting. This page also gives you realtime CA information, etc if that's something you're interested in.

Also, FYI most of the rest of the system logs are available via http://192.168.1.1/debug.htm, hit "Start Capture", do stuff, come back and then hit "Save Debug File" which will download a zip full of your logs. If you want to do a little more in-depth, select "Start Debug Log Capture when boot up" and come back and hit Save Log after you've run into any issue.

Just general FYI, this one is based on OpenWrt 15.0.5.1 (so about 8 years old). I'm going to keep playing around and see if I can build Wireguard for this thing at least. Will update thread if anything interesting comes up.