Cisco Nexus 1000V Layer 2 Switching Configuration Guide, Release 4.0(4)SV1(1)
Configuring the MAC Address Table
Downloads: This chapterpdf (PDF - 153.0KB) The complete bookPDF (PDF - 2.17MB) | Feedback

MAC Address Table

Table Of Contents

MAC Address Table

Information About MAC Address Tables

Guidelines and Limitations

Configuring a Static MAC Address

Configuring the Aging Time for the MAC Table

Clearing Dynamic Addresses from the MAC Address Table

Verifying the Layer 2 Switching Configuration

Layer 2 Switching Example Configuration

Default Setting

Additional References

Related Documents

Standards

Feature History for the MAC Address Table


MAC Address Table



Note For information about creating interfaces, see the document,
Cisco Nexus 1000V Interface Configuration Guide, Release 4.0(4)SV1(1).


This chapter includes the following topics:

Information About MAC Address Tables

Guidelines and Limitations

Configuring a Static MAC Address

Clearing Dynamic Addresses from the MAC Address Table

Verifying the Layer 2 Switching Configuration

Layer 2 Switching Example Configuration

Default Setting

Additional References

Feature History for the MAC Address Table

Information About MAC Address Tables

Layer 2 ports correlate the MAC address on a packet with the Layer 2 port information for that packet using the MAC address table. A MAC address table is built using the MAC source addresses of the frames received. When a frame is received for a MAC destination address not listed in the address table, the frame is flooded to all LAN ports of the same VLAN with the exception of the port that received the frame. When the destination station replies, the relevant MAC source addresses and port IDs are added to the address table. Then subsequent frames are forwarded to a single LAN port without flooding all LAN ports.

You can configure MAC addresses, which are called static MAC addresses, to statically point to specified interfaces on the device. These static MAC addresses override any dynamically learned MAC addresses on those interfaces. You cannot configure broadcast or multicast addresses as static MAC addresses. The static MAC entries are retained across reboots.

The address table can store up to 100 address entries. An aging timer triggers removal of addresses from the table when they remain inactive for 300 seconds. The aging timer can be configured on a global basis but not per VLAN. The aging timer is configurable on a global basis but not on a per VLAN basis.

You can configure the length of time an entry remains in the MAC address table, clearing the table, and so forth.

Guidelines and Limitations

Keep in mind the following guidelines for configuring MAC addresses:

The forwarding table for each VLAN in a VEM can store up to 1024 MAC addresses.

Static MAC address entries cannot be configured on an interfaces where port security is enabled. Instead, use the following command in Interface Configuration mode:

n1000v(config-if)# switchport port-security mac address xxxx.yyyy.zzzz [vlan vlan id]. 

For more information, see the Cisco Nexus 1000V Security Configuration Guide, Release 4.0(4)SV1(1).

The NX-OS software explicitly prohibits configuring port security on ports that have a static MAC addresses configured on the following VLANs:

the access VLAN of an access port

the native VLAN of a trunk port

Configuring a Static MAC Address

Use this procedure to configure a MAC address to statically point to a specific interface.

BEFORE YOU BEGIN

Before beginning this procedure, you must know or do the following:

You are logged in to the CLI in EXEC mode.

You cannot configure broadcast or multicast addresses as static MAC addresses.

Static MAC addresses override dynamically-learned MAC addresses on an interface.


Note Be aware that the NX-OS commands may differ from those used in Cisco IOS.


SUMMARY STEPS

1. config t

2. mac address-table static mac address vlan vlan-id {[drop | interface {type number | | port-channel number]}

3. exit

4. show mac address-table static

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

config t


Example:

n1000v# config t

n1000v(config)#

Places you into CLI Global Configuration mode.

Step 2 

mac address-table static mac_address vlan vlan-id {[drop | interface {type number} | port-channel number]}


Example:

n1000v(config)# mac address-table static 12ab.47dd.ff89 vlan 3 interface ethernet 2/1

Adds a static MAC address in the Layer 2 MAC address table and saves it in the running configuration.

Interface can be specified as either of the following:

ethernet slot/port

veth number

Step 3 

exit


Example:

n1000v(config)# exit

n1000v#

Exits Global Configuration mode and returns you to EXEC mode.

Step 4 

show mac address static


Example:

n1000v# show mac address static

(Optional) Displays the static MAC addresses.

Step 5 

copy running-config startup-config


Example:

n1000v# copy running-config startup-config

(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.

Example:
n1000v# config t 
n1000v(config)# mac address static 12ab.47dd.ff89 vlan 3 interface ethernet 2/1
n1000v# show mac address static
Legend: 
        * - primary entry, G - Gateway MAC, (R) - Routed MAC
        age - seconds since last seen
   VLAN     MAC Address      Type      age     Secure  NTFY   Ports
---------+-----------------+--------+---------+------+------+----------------
G     -    12ab.47dd.ff89    static       -     False  False  eth2/1

n1000v# 

Configuring the Aging Time for the MAC Table

Use this procedure to configure the amount of time that a packet source MAC address and port on which it was learned remain in the MAC table containing the Layer 2 information.


Note You can also configure MAC aging time in interface configuration mode or VLAN configuration mode.


BEFORE YOU BEGIN

Before beginning this procedure, you must know or do the following:

You are logged in to the CLI in EXEC mode.


Note Be aware that the Cisco NX-OS commands may differ from those used in Cisco IOS.


SUMMARY STEPS

1. config t

2. mac address-table aging-time seconds

3. exit

4. show mac address-table

5. copy running-config startup-config

DETAILED STEPS

 
Command
Purpose

Step 1 

config t


Example:

n1000v# config t

n1000v(config)#

Places you into CLI Global Configuration mode.

Step 2 

mac address-table aging-time seconds


Example:

n1000v(config)# mac address-table aging-time 600

Specifies and saves in the running configuration the amount of time that will elapse before an entry in the Layer 2 MAC address table is discarded.

Allowable entries:

120 to 918000 seconds (default is 300)

If you specify zero (0), MAC aging is disabled.

Step 3 

exit


Example:

n1000v(config)# exit

n1000v#

Exits Global Configuration mode and returns you to EXEC mode.

Step 4 

show mac address-table aging-time


Example:

n1000v# show mac address-table aging-time

(Optional) Displays the aging time in the MAC address table.

Step 5 

copy running-config startup-config


Example:

n1000v# copy running-config startup-config

(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.

Example:
n1000v# config t 
n1000v(config)# mac address-table aging-time 600
n1000v(config)#

Clearing Dynamic Addresses from the MAC Address Table

Use this procedure to clear all dynamic Layer 2 entries from the MAC address table.

BEFORE YOU BEGIN

Before beginning this procedure, you must know or do the following:

You are logged in to the CLI in EXEC mode.


Note Be aware that the NX-OS commands may differ from those used in Cisco IOS.


SUMMARY STEPS

1. clear mac address-table dynamic {address mac_addr} {interface {type number] | port-channel number | vlan vlan_id}

2. show mac address-table

DETAILED STEPS

 
Command
Purpose

Step 1 

clear mac address-table dynamic {address mac_addr} {interface [type number] | port-channel number} {vlan vlan_id}


Clears the dynamic address entries from the Layer 2 MAC address table.

Interface can be specified as either of the following:

ethernet slot/port

veth number

 

Example:

n1000v# clear mac address-table dynamic

n1000v#

This example clears the entire MAC address table of all dynamic entries.

 

Example:

n1000v# clear mac address-table dynamic vlan 5

n1000v#

This example clears only those dynamic MAC addresses learned on VLAN 5 from the MAC address table.

Step 2 

show mac address-table


Example:

n1000v# show mac address-table

(Optional) Displays the MAC address table.

Verifying the Layer 2 Switching Configuration

Use the following commands to display and verify the Layer 2 MAC address configuration.

Command
Purpose

show mac address-table

Displays the MAC address table.

show mac address-table static

Displays information about the MAC address table static entries.

show mac address-table aging-time

Displays the aging time in the MAC address table.

show interface [<interface>] mac

Displays the MAC addresses and the burn-in MAC address for an interface.



Note The Cisco Nexus 1000VMAC address table does not display multicast MAC addresses.


Layer 2 Switching Example Configuration

The following example shows how to add a static MAC address:

n1000v# configure terminal
n1000v(config)# mac address-table static 0000.0000.1234 vlan 10 interface ethernet 2/15
n1000v(config)# mac address-table aging-time 120

Default Setting

Table 2-1 lists the default setting for the MAC address aging time.

Table 2-1 Default MAC Address Aging Time 

Parameters
Default

Aging time

300 seconds


Additional References

For additional information related to implementing Layer 2 switching, see the following sections:

Related Documents

Standards

Related Documents

Related Topic
Document Title

Interfaces

Cisco Nexus 1000V Interface Configuration Guide, Release 4.0(4)SV1(1)

Port-Profiles

Cisco Nexus 1000V Port Profile Configuration Guide, Release 4.0(4)SV1(1)

System management

Cisco Nexus 1000V System Management Configuration Guide, Release 4.0(4)SV1(1)

Release Notes

Cisco Nexus 1000V Release Notes, Release 4.0(4)SV1(1)

Layer 2 commands

Cisco Nexus 1000V Command Reference, Release 4.0(4)SV1(1)


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.


Feature History for the MAC Address Table

This section provides the MAC address tables release history.

Feature Name
Releases
Feature Information

MAC Address Tables

4.0(4)SV1(1)

This feature was introduced.