3Com PathBuilder S200 Series Owner's Manual page 59

Multicast Link When a multicast/broadcast frame comes from a link with the Multicast Protect Flag
Protect Flag
set, and if its source address is not found in the Permanent Station Address list, the
frame is dropped.
When a multicast/broadcast frame is sent out over a link with the Multicast Protect
Flag set, and if its destination address is not found in the Permanent Station Address
List, the frame is dropped.
Once the Multicast Protect Flag is set for a link, source address learning for
multicast/broadcast frames is stopped for that link totally and all the addresses that
were learned before are moved into the Permanent Station Address List.
Setting or Clearing of Multicast Link Protect Flag is performed using the LAN
Control menu located in the Main menu.
Bridging
T0008-16F
Transparent Bridging for Ethernet LANs
55
Release 5.2M