Capturing and transmitting UDP stream FFMpeg?

Question

fmpeg

There is a machine (in the future there will be an encoder receiving a signal from a satellite) that broadcasts UDP Multicast, it broadcasts it to the eth0 server interface, after that I want to capture this stream from eth0 and transfer it to eth1 (with a real ip) in RTMP or HLS, I use it for this ffserver+ffmpeg and tried NGINX + FFMpeg.
The question is how? Can't multicast