H3C S7500 Series User manual

Operation Manual – MAC Address Table
H3C S7500 Series Ethernet Switches Table of Contents
i
Table of Contents
Chapter 1 MAC Address Table Management.............................................................................. 1-1
1.1 Overview............................................................................................................................1-1
1.1.1 Introduction to MAC Address Learning...................................................................1-1
1.1.2 Entries in a MAC Address Table.............................................................................1-3
1.2 Configuring MAC Address Table Management.................................................................1-3
1.2.1 MAC Address Table Configuration Task List..........................................................1-3
1.2.2 Configuring a MAC Address Entry..........................................................................1-4
1.2.3 Setting the Aging Time for MAC Address Entries...................................................1-4
1.2.4 Setting the Maximum Number of MAC Addresses a Port can Learn......................1-5
1.2.5 Disabling MAC Address Learning...........................................................................1-5
1.2.6 Configuring MAC Address Learning Synchronization Between Board Chips.........1-6
1.2.7 Setting the Processing Method for Specific Packets ..............................................1-7
1.3 Displaying MAC Address Configuration ............................................................................ 1-7
1.4 Configuration Example ......................................................................................................1-7
1.4.1 Network Requirements............................................................................................1-7
1.4.2 Configuration Procedure.........................................................................................1-7

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Chapter 1 MAC Address Table Management
When configuring MAC address table management, go to these sections for
information you are interested in:
zOverview
zConfiguring MAC Address Table Management
zDisplaying MAC Address Configuration
zConfiguration Example
Note:
This chapter describes the management of static and dynamic MAC address entries.
For information on the management of multicast MAC address entries, refer to the
section related to multicast protocol in H3C S7500 Series Ethernet Switches Operation
Manual.
1.1 Overview
1.1.1 Introduction to MAC Address Learning
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:
zDestination MAC address
zID of the VLAN which a port belongs to
zForwarding port number
Upon receiving a packet, a switch queries its MAC address table forthe 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.

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Port2
zIf the MAC address table already contains MAC-SOURCE, the switch updates the
corresponding MAC address entry.
zIf 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.
Port1
MAC address Port
MAC A 1
MAC B 1
MAC C 2
MAC D 2
MAC A
MAC B
MAC C
MAC D
Figure 1-1 Packets forwarded by using a MAC address table
After learning the source address of the packet, the switch searches the MAC address
table for the destination MAC address of the received packet:
zIf it finds a match, it directly forwards the packet.
zIf it finds no match, it forwards the packet to all ports, except the receiving port,
within the VLAN to which the receiving port belongs. Normally, this is referred to as
broadcasting the packet.
After broadcasting the packet, the switch will do one of the following based on whether
it receives a response packet:
zIf the network device returns a packet to the switch, this indicates the packet has
been sent to the destination device. The MAC address of the device is carried in
the packet. The switch adds the new MAC address to the MAC address table
through address learning. After that, the switch can directly forward other packets
destined for the same network device by using the newly added MAC address
entry.
zIf the destination device does not respond to the packet, this indicates that the
destination device is unreachable or that the destination device receives the
packet but gives no response. In this case, the switch still cannot learn the MAC
address of the destination device. Therefore, the switch will still broadcast any
other packet with this destination MAC address.
To fully utilize a MAC address table, which has a limited capacity, the switch uses an
aging mechanism for updating the table. That is, the switch removes the MAC address
entries related to a network device if no packet is received from the device within the
aging time. Aging time only applies to dynamic MAC address entries.

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You can manually configure (add or modify) a static or dynamic MAC address entry
based on the actual network environment.
Note:
The switch learns only unicast addresses by using the MAC address learning
mechanism but directly drops any packet with a broadcast source MAC address.
1.1.2 Entries in a MAC Address Table
Entries in a MAC address table fall into the following two categories according to their
characteristics and configuration methods:
zStatic MAC address entry: Also known as permanent MAC address entry. This
type of MAC address entries are added/removed manually and can not age out by
themselves. Using static MAC address entries can reduce broadcast packets
remarkably and are suitable for networks where network devices seldom change.
zDynamic MAC address entry: This type of MAC address entries ages out after the
configured aging time. They are generated by the MAC address learning
mechanism or configured manually.
Table 1-1 lists the different types of MAC address entries and their characteristics.
Table 1-1 Characteristics of different types of MAC address entries
MAC address
entry Configuration method Aging time Reserved or not at
reboot (if the
configuration is saved)
Static MAC
address entry Manually configured Unavailable Yes
Dynamic MAC
address entry
Manually
configured or
generated by MAC
address learning
mechanism
Available No
1.2 Configuring MAC Address Table Management
1.2.1 MAC Address Table Configuration Task List
Complete the following tasks to configure MAC address table:

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Task Remarks
Configuring a MACAddress Entry Required
Setting the Aging Time for MAC Address Entries Optional
Setting the Maximum Number of MAC Addresses a Port can Learn Optional
Disabling MAC Address Learning Optional
Configuring MACAddress Learning Synchronization Between
Board Chips Optional
Setting the Processing Method for Specific Packets Optional
1.2.2 Configuring a MAC Address Entry
You can add, modify, or remove one MAC address entry, remove all the MAC address
entries (unicast MAC addresses only) concerning a specific port, or remove a specific
type of MAC address entries (dynamic or static).
Follow these steps to add a MAC address entry:
To do… Use the command… Remarks
Enter system view system-view —
Add a MAC
address entry
mac-address { static | dynamic }
mac-address interface interface-type
interface-number vlan vlan-id Required
Caution:
For a MAC address entry to be added, the port specified by the interface keyword must
belong to the VLAN specified by the vlan keyword in the command. Otherwise, the
entry cannot be added.
1.2.3 Setting the Aging Time for MAC Address Entries
Setting aging time properly helps implement effective MAC address aging. The aging
time that is too long or too short results in a large amount of broadcast packets
wandering across the network and decreases the performance of the switch.
zIf the aging time is too long, excessive invalid MAC address entries maintained by
the switch may fill up the MAC address table. This prevents the MAC address
table from varying with network changes in time.

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zIf the aging time is too short, the switch may remove valid MAC address entries.
This decreases the forwarding performance of the switch.
Follow these steps to set aging time for MAC address entries:
To do… Use the command… Remarks
Enter system view system-view —
Set the aging time of MAC
address entries mac-address timer
{ aging age | no-aging }
Required
The default aging time is
300 seconds.
This command is used in system view and applies to all ports. Aging applies to only
dynamic MAC addresses that are learnt or configured to age out.
Normally, you are recommended to use the default aging time, namely, 300 seconds.
The no-aging keyword specifies that MAC address entries do not age out.
1.2.4 Setting the Maximum Number of MAC Addresses a Port can Learn
The MAC address learning mechanism enables an Ethernet switch to acquire the MAC
addresses of the network devices on the segment connected to the ports of the switch.
The switch directly forwards the packets destined for these MAC addresses. An
oversized MAC address table may decrease the forwarding performance of the switch.
By setting the maximum number of MAC addresses that can be learnt from individual
ports, you can control the number of the MAC address entries the MAC address table
can dynamically maintains. If you have set the maximum number of MAC addresses
that a port can learn to count, the port stops learning MAC addresses when the number
of MAC addresses learned by the port reaches count.
Follow these steps to set the maximum number of MAC addresses a port can learn:
To do… Use the command… Remarks
Enter system view system-view —
Enter Ethernet port view interface interface-type
interface-number —
Set the maximum number
of MAC addresses the
port can learn
mac-address
max-mac-count count
Required
By default, the number of
the MAC addresses a port
can learn is not limited.
1.2.5 Disabling MAC Address Learning
To gain better control over network security, you can use the following commands to
disable the current port from learning MAC addresses.

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Follow these steps to disable the current port from learning MAC addresses:
To do… Use the command… Remarks
Enter system view system-view —
Enter Ethernet port view interface interface-type
interface-number —
Disable the current port
from learning MAC
addresses
mac-address
mac-learning disable
Required
By default, the port is
enabled to learn MAC
addresses.
Note:
zDo not use the mac-address mac-learning disable command together with
related 802.1x commands in Ethernet port view.
zDo not use the mac-address mac-learning disable command together with the
mac-address max-mac-count command.
1.2.6 Configuring MAC Address Learning Synchronization Between Board
Chips
If there are multiple chips on a board, each chip can learn only the MAC addresses of
the data flow it handles. If a chip receives a packet whose MAC address entry is stored
in another chip, it broadcasts the packet.
You can configure MAC address learning synchronization between board chips to
synchronize MAC address entries between chips. This reduces broadcasting of
unknown packets, lowers switch processing load, and improves network utilization.
Follow these steps to configure MAC address learning synchronization between board
chips:
To do… Use the command… Remarks
Enter system view system-view —
Enable MAC address
learning synchronization
between board chips
mac-address
learning
synchronization
Optional
By default, MAC address
learning synchronization
between board chips is
disabled.

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1.2.7 Setting the Processing Method for Specific Packets
Follow these steps to set the packet processing method of a switch when it receives a
packet whose destination MAC address is the bridge MAC address of the switch:
To do… Use the command… Remarks
Enter system view system-view —
Enable the switch to pass
the packet whose
destination MAC address is
the bridge MAC address of
the switch to the CPU for
processing
bridgemactocpu
enable
Optional
By default, packets with
the destination MAC
address being the bridge
MAC address of the
switch are not passed to
the CPU for processing.
Disable the switch from
passing the packet whose
destination MAC address is
the bridge MAC address of
the switch to the CPU for
processing
bridgemactocpu
disable Optional
1.3 Displaying MAC Address Configuration
To do… Use the command… Remarks
Display information about the
MAC address table display mac-address
[ display-option ]
Display the aging time of the
dynamic MAC address entries
in the MAC address table
display mac-address
aging-time
Available in any
view.
1.4 Configuration Example
1.4.1 Network Requirements
zLog into the switch through the console port and enable address table
configuration.
zSet the aging time of dynamic MAC address entries to 500 seconds.
zAdd a static MAC address entry 000f-e235-dc71 for port Ethernet 2/0/2 (assuming
that the port belongs to VLAN 1).
1.4.2 Configuration Procedure
# Enter system view.
<H3C> system-view

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[H3C]
# Add a MAC address, with the VLAN, ports, and states specified.
[H3C] mac-address static 000f-e235-dc71 interface Ethernet 2/0/2 vlan 1
# Set the aging time of dynamic MAC addresses to 500 seconds.
[H3C] mac-address timer aging 500
# Display the information about the MAC address entries in system view.
[H3C] display mac-address interface Ethernet 2/0/2
MAC ADDR VLAN ID STATE PORT INDEX AGING TIME(s)
000f-e235-dc71 1 Config static Ethernet2/0/2 NOAGED
000f-e200-5503 1 Learned Ethernet2/0/2 AGING
000f-e200-5548 1 Learned Ethernet2/0/2 AGING
--- 3 mac address(es) found on port Ethernet2/0/2 ---