Cabletron Systems Fast Network 10, User Manual

Page: 19 / 132

Overview
Fast Network 10 User Guide Page 1-9
automatically reconfigured by the Spanning Tree protocol to create an
alternate path to the LAN.
1.5.2 FN10 Bridge Address Table
The FN10 creates and maintains a dynamic database of addresses called
the Bridge Address Table. The FN10 examines every packet to determine
its source address and LAN segment origin. It then compares the source
address and segment information it finds to the entries in the Bridge
Address Table.
If a packet’s address is not already stored in the Bridge Address Table, the
FN10 adds the learned address, associated segment number, and a timer
value that indicates the age of the observation. Consequently, the FN10
knows the address and associated segment number the next time it sees
that address. By using the information stored in the Bridge Address Table,
the FN10 is able to quickly forward each packet to the correct LAN
segment.
The FN10 learns addresses from all packets, including data transmissions
and “keep alive” packets (packets sent by an idle station to let other
stations know it is present and functional). When devices are added to the
network, removed from it, or relocated, you do not have to reconfigure the
FN10. The FN10 automatically learns new device addresses, recognizes
when a previously used address is missing, or when a device has been
moved to a new LAN segment.
An address stored in the Bridge Address Table is discarded if there is no
subsequent activity from that address after a configured length of time
(five minutes by default). This aging process ensures that the Bridge
Address Table is continually updated.
Typically, addresses are continually added to and deleted from the Bridge
Address Table, reflecting the dynamic nature of internetwork traffic.
However, you can change an address from dynamic to static if you do not
want the entry in the Bridge Address Table to get discarded.
Each dynamic entry includes:
• An Ethernet MAC address