Configuring The Mac Address Table; Overview; How A Mac Address Table Entry Is Created - HP 3100 Series Configuration Manual

Configuring the MAC address table

This feature covers only the unicast MAC address table. For information about configuring static
multicast MAC address table entries for IGMP snooping and MLD snooping, see IP Multicast
Configuration Guide.
The MAC address table can contain only Layer 2 Ethernet ports and Layer 2 aggregate interfaces.
The MAC address table configuration tasks are all optional can be performed in any order.

Overview

To reduce single-destination packet flooding in a switched LAN, an Ethernet device uses a MAC
address table for forwarding frames through unicast instead of broadcast. An MAC address table
entry contains a destination MAC address, the outgoing interface corresponding to the MAC address,
and the ID of the VLAN to which the outgoing interface belongs. When forwarding a
single-destination frame, the device first looks up the MAC address of the frame in the MAC address
table for a match. If the switch finds an entry, it forwards the frame out of the outgoing port in the entry.
If the switch does not find an entry, it floods the frame out of all but the incoming port.
To view MAC address table information, use the display mac-address command, as follows:
<Sysname> display mac-address
MAC ADDR
000f-e201-0101
--- 1 mac address(es) found

How a MAC address table entry is created

The switch automatically obtains entries in the MAC address table, or you can add them manually.
MAC address learning
The device can automatically populate its MAC address table by obtaining the source MAC
addresses (called "MAC address learning") of incoming frames on each port.
When a frame arrives at a port, Port A, for example, the device performs the following tasks:
Verifies the source MAC address (for example, MAC-SOURCE) of the frame.
1.
Looks up the source MAC address in the MAC address table.
2.
If an entry is found, the device updates the entry.
If no entry is found, the device adds an entry for MAC-SOURCE and Port A.
After obtaining this source MAC address, when the device receives a frame destined for
3.
MAC-SOURCE, the device finds the MAC-SOURCE entry in the MAC address table and
forwards the frame out of Port A.
The device performs this learning process each time it receives a frame from an unknown source
MAC address, until the MAC address table is fully populated.
Manually configuring MAC address entries
With dynamic MAC address learning, a device does not distinguish between illegitimate and
legitimate frames, which can invite security hazards. For example, when a hacker sends frames with
a forged source MAC address to a port different from the one to which the real MAC address is
connected, the device creates an entry for the forged MAC address, and forwards frames destined
for the legal user to the hacker instead.
VLAN ID STATE
1 Learned
---
PORT INDEX
Ethernet1/0/1
19
AGING TIME(s)
AGING