Cabletron Systems NBR-620, NBR-420, NBR-220 manual D.4 BRIDGING FUNCTIONALITY

Bridging Functionality

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.

NBR-SERIES Installation Guide Page D-3