Key Bridging Concepts; Learning Addresses; Aging Addresses; Forwarding, Filtering, And Flooding Packets - 3Com corebuilder 3500 Implementation Manual

116 C 7: B
HAPTER RIDGE
Key Bridging
Concepts

Learning Addresses

Aging Addresses

Forwarding, Filtering,
and Flooding Packets
-W B P P
IDE AND RIDGE ORT
Before you configure bridge-wide or bridge port parameters, review the
following key concepts.
Bridges learn addresses so that they can determine which packets to
forward from one bridge port to another. A bridge learns addresses by
processing the network traffic that it receives. For a bridge to learn the
address of a station on the network (a source address), that station must
transmit a packet. Addresses that are learned are called dynamic
addresses.
Each bridge maintains a table, called the address table, which lists each
learned address and associates it with a port. (The address table also lists
manually configured addresses called static addresses.)
The system can store up to 32 K addresses in its address table.
A dynamic address remains in the bridge's address table as long as the
station to which it relates regularly transmits packets through the bridge.
If the station does not transmit within a specified period of time, the
dynamic address is aged out (deleted) from the address table.
Address aging ensures that, if a station moves to a different segment on
the network, packets are no longer be forwarded to the station's former
location. Address aging is necessary because a bridge can learn only a
finite number of addresses.
A bridge filters, floods, or forwards packets by comparing:
The packet's destination address to the source addresses in the
bridge's address table.
The destination bridge port (if known) to the port on which the packet
was received.
ARAMETERS