BUM = Broadcast, Unknown unicast and Multicast.
Generic term to describe the three types of Ethernet modes:
- Broadcast Ethernet
- Unicast Ethernet
- Multicast Ethernet
In all Layer 2 networking, the broadcast and multicast modes are major scaling challenges and create single failure domains. The term BUM is used extensively in L2 DCI discussions.

Pingback: How TRILL (and SPB) can reduce STP risk and mitigate impact — My EtherealMind
Pingback: What’s Happening Inside an Ethernet Switch ? ( Or Network Switches for Virtualization People ) — EtherealMind