Cabletron Systems NBR-420 - Manual (Page 71)

Bridging Functionality
NBR-SERIES Installation Guide Page D-3
D.4 BRIDGING FUNCTIONALITY
The NBR automatically configures itself as a bridge between channels A,
B, C, D, E, and F for a six port bridge maximum. The IEEE 802.1d
compliant bridge function supports multi-port bridging, the IETF Bridge
MIB, Special Filtering Database, and Spanning Tree protocol.
The NBR incorporates IEEE 802.1d or DEC Spanning Tree Algorithms
(user selectable), allowing bridges in parallel between segments as
backup paths for fault tolerance. These parallel bridges remain in a
standby condition until the primary path fails.
When the NBR receives frames (traffic) from any of the Ethernet
channels, it places the frame in its buffer memory, and then goes through
an information gathering/decision making process of what to do with
those frames. The device determines the following:
• Where the frames came from (source address), and if it has seen
frames from that address before (learning)
• Where the frames are going (destination address), and if it has received
frames from that address before (filtering database lookup)
• Whether to forward (send on) or filter (discard) any of these frames
(database lookup result)
• What channel to use if it must forward the frames
When the NBR forwards a frame, it extracts the frame buffer data
(including the source and destination address), then transmits the frame
onto the appropriate channel.