Собственно, вам надо три строчки заменить:
- # This script create bridge between two network interfaces
+ # This script creates bridge between two network interfaces- # only packets with multicast dst mac addr forwarded trouth bridge and (!) not pass to network stack
+ # only packets with multicast destination mac address are forwarded through the bridge and (!) are not passed to network stack
- echo "This create bridge beetwen two IFs for IGMP, and UDP from upstreamIF to downstreamIF1"
+ echo "This will create bridge between two interfaces for IGMP, and UDP from upstreamIF to downstreamIF1"