Mac Address Table Management; Overview - 3Com 7757 Configuration Manual

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Overview

Introduction to MAC
Address Learning
MAC A
n
This chapter describes the management of static and dynamic MAC address
entries. For information on the management of multicast MAC address entries,
refer to "Multicast Overview" on page 413.
An Ethernet switch maintains a MAC address table to forward packets quickly. A
MAC address table is a port-based Layer 2 address table. It is the base for Ethernet
switch to perform Layer 2 packet forwarding. Each entry in a MAC address table
contains the following fields:
Destination MAC address
■
ID of the VLAN which a port belongs to.
■
Forwarding port number.
■
Upon receiving a packet, a switch queries its MAC address table for the
forwarding port number according to the destination MAC address carried in the
packet and then forwards the packet through the port.
The dynamic address entries (not configured manually) in the MAC address table
are learned by the Ethernet switch. When an Ethernet switch learns a MAC
address, the following occurs:
When a switch receives a packet from one of its ports (referred to as Port 1), the
switch extracts the source MAC address (referred to as MAC-SOURCE) of the
packet and considers that the packets destined for MAC-SOURCE can be
forwarded through Port 1.
If the MAC address table already contains MAC-SOURCE, the switch updates
■
the corresponding MAC address entry.
If MAC-SOURCE does not exist in the MAC address table, the switch adds
■
MAC-SOURCE and Port 1 as a new MAC address entry to the MAC address
table.
T
DDRESS ABLE
M
ANAGEMENT