how to receive the udp packets under 3 networks

[Suken Woo]

hi folks
on my one box( runnig gateway_enable under 4.9-RELEASE-p1) that connected 3
networks(if0==192.168.168/25 192.168.168.128/25 if3==10.3). and the udp
packet
comming from the if3 and now how can i enable my box and that let it
forward the
udp packet to 192.168. networks???? is set mrouted???? and I don't know
much about
mroute.....:(

thanks in advance for any info......