I would be really curious to see your packet captures. 68.28.x.x is CDMA on my Airave 3 and 4, and 68.31.x.x is LTE (and wifi calling). It seems like yours doesn't fit that in CDMA nor LTE. Definitely report back the IPs that you discover. You can also let it power on and dump the state table on your firewall. Look for the two connections on UDP port 4500. That's a quick and easy way to grab the IPs. Sent from my Pixel 3 XL using Tapatalk
So I put in the filter and unfortunately, it did not stop it from connecting up to LTE on reboot. Just for kicks, I did try blocking 68.31.0.* and 68.31.*.*, but that only stopped the CDMA side from establishing a connection :/. Guess I am going to have to do a packet capture and see where the heck it is getting its info on boot.
Or maybe better yet, see if I can get Sprint to send me an MB Gold with the 1xRTT boost module... I am getting 60mbit/5mbit consistently now on my MB3.