- Preface
- New and Changed Information
- Overview
- Configuring Ethernet Interfaces
- Configuring VLANs
- Configuring Private VLANs
- Configuring Access and Trunk Interfaces
- Configuring EtherChannels
- Configuring Virtual Port Channels
- Configuring Rapid PVST+
- Configuring Multiple Spanning Tree
- Configuring STP Extensions
- Configuring LLDP
- Configuring the MAC Address Table
- Configuring IGMP Snooping
- Configuring Traffic Storm Control
- Configuring the Fabric Extender
- Index
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.0(2)N2(1)
Bias-Free Language
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- Updated:
- July 13, 2017
Chapter: Configuring the MAC Address Table
Configuring the MAC Address Table
All Ethernet interfaces on Cisco Nexus 5000 Series switches maintain media access control (MAC) address tables. This chapter describes the configuration of the MAC address tables. It includes the following sections:
Information About MAC Addresses
To switch frames between LAN ports, the switch maintains an address table. When the switch receives a frame, it associates the media access control (MAcC) address of the sending network device with the LAN port on which it was received.
The switch dynamically builds the address table by using the MAC source address of the frames received. When the switch receives a frame for a MAC destination address not listed in its address table, it floods the frame to all LAN ports of the same VLAN except the port that received the frame. When the destination station replies, the switch adds its relevant MAC source address and port ID to the address table. The switch then forwards subsequent frames to a single LAN port without flooding all LAN ports.
You can also enter a MAC address, which is termed a static MAC address, into the table. These static MAC entries are retained across a reboot of the switch.
In addition, you can enter a multicast address as a statically configured MAC address. A multicast address can accept more than one interface as its destination.
The address table can store a number of unicast and multicast address entries without flooding any frames. The switch uses an aging mechanism, defined by a configurable aging timer, so if an address remains inactive for a specified number of seconds, it is removed from the address table.
Configuring MAC Addresses
Configuring a Static MAC Address
You can configure MAC addresses for the switch. These addresses are static MAC addresses.
 Note |
You can also configure a static MAC address in interface configuration mode or VLAN configuration mode. |
1. switch# configure terminal
2. switch(config-)# mac-address-table static mac_address vlan vlan-id {drop | interface {type slot/port} | port-channel number} [auto-learn]
3. (Optional) switch(config-)# no mac-address-table static mac_address vlan vlan-id
DETAILED STEPS
This example shows how to put a static entry in the MAC address table:
switch# configure terminal
switch(config)# mac-address-table static 12ab.47dd.ff89 vlan 3 interface ethernet 2/1
You can use the mac-address-table static command to assign a static MAC address to a virtual interface.
Configuring the Aging Time for the MAC Table
You can configure the amount of time that an entry (the packet source MAC address and port that packet ingresses) remain in the MAC table.
Note |
You can also configure MAC aging time in interface configuration mode or VLAN configuration mode. |
1. switch# configure terminal
2. switch(config)# mac-address-table aging-time seconds [vlan vlan_id]
DETAILED STEPS
This example shows how to set the aging time for entries in the MAC address table to 600 seconds (10 minutes):
switch# configure terminal
switch(config)# mac-address-table aging-time 600
Clearing Dynamic Addresses from the MAC Table
You can clear all dynamic entries in the MAC address table.
| Command |
Purpose |
|---|---|
| switch(config)# clear mac-address-table dynamic {address mac-addr} {interface [type slot/port | port-channel number} {vlan vlan-id} | Clears the dynamic address entries from the MAC address table. |
This example shows how to clear the dynamic entries in the MAC address table:
switch# clear mac-address-table dynamic
Verifying the MAC Address Configuration
To display MAC address configuration information, perform one of these tasks:
| Command |
Purpose |
|---|---|
| switch# show mac-address-table aging-time | Displays the MAC address aging time for all VLANs defined in the switch. |
| switch# show mac-address-table | Displays the contents of the MAC address table. |
This example shows how to display the MAC address table:
switch# show mac-address-table
VLAN MAC Address Type Age Port
---------+-----------------+-------+---------+------------------------------
1 0018.b967.3cd0 dynamic 10 Eth1/3
1 001c.b05a.5380 dynamic 200 Eth1/3
Total MAC Addresses: 2
This example shows how to display the current aging time:
switch# show mac-address-table aging-time
Vlan Aging Time
----- ----------
1 300
13 300
42 300
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