Mac Address Table Management; Overview; Introduction To Mac Address Table; Introduction To Mac Address Learning - 3Com 4200G 12-Port Configuration Manual

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MAC Address Table Management

This chapter describes the management of static, dynamic, and blackhole MAC address entries. For
information about the management of multicast MAC address entries, refer to the part related to
multicast protocol.

Overview

Introduction to MAC Address Table

An Ethernet switch is mainly used to forward packets at the data link layer, that is, transmit the packets
to the corresponding ports according to the destination MAC address of the packets. To forward packets
quickly, a switch maintains a MAC address table, which is a Layer 2 address table recording the MAC
address-to-forwarding port association. Each entry in a MAC address table contains the following fields:
Destination MAC address
ID of the VLAN which a port belongs to
Forwarding egress port numbers on the local switch
When forwarding a packet, an Ethernet switch adopts one of the two forwarding methods based upon
the MAC address table entries.
Unicast forwarding: If the destination MAC address carried in the packet is included in a MAC
address table entry, the switch forwards the packet through the forwarding egress port in the entry.
Broadcast forwarding: If the destination MAC address carried in the packet is not included in the
MAC address table, the switch broadcasts the packet to all ports except the one receiving the
packet.

Introduction to MAC Address Learning

MAC address table entries can be updated and maintained through the following two ways:
Manual configuration
MAC address learning
Generally, the majority of MAC address entries are created and maintained through MAC address
learning. The following describes the MAC address learning process of a switch:
1) As shown in
User B, the packet from User A needs to be transmitted to GigabitEthernet 1/0/1. At this time, the
switch records the source MAC address of the packet, that is, the address "MAC-A" of User A to the
MAC address table of the switch, forming an entry shown in
Figure 1-1, User A and User B are both in VLAN 1. When User A communicates with
Figure
1-1
1-2.