I'm in the same situation as the OP in that I'm trying to get my SXT LTE device to pass the public LTE IP to my Synology RT2600ac. I have tried for several hours this evening to get this working by following the passthrough example linked above in the Mikrotik wiki and also a post by another user here ( viewtopic.php?p=690922
) but I just keep locking myself out of the SXT and having to reset it and start again.
I'm by no means a networking expert but I am familiar with most aspects of networking including VLANs and have an HP managed switch which I was hoping to use to retain management access to the SXT once it is in passthrough mode. I just can't quite put it all together. I've tried removing ether1 from the default bridge to allow me to setup the passthrough from lte1 because it said you can't set up passthrough on a slave interface. I also tried setting up passthrough to the bridge interface. Invariably I only get so far before I lose comms with the SXT and have to reset it again. Sometimes I can still ping the SXT but can't get into WebFig. Not sure why.
Any advice would be much appreciated.