Brocade 6910 Ethernet Access Switch Diagnostic Guide
Brocade 6910 Ethernet Access Switch Diagnostic Guide
2.2.0.0
Part Number: 53-1002653-01
documentation@brocade.com


Layer 2 Protocol Diagnostics : MAC address learning

MAC address learning
In MAC address learning, the source MAC address of each received packet is stored so that future packets destined for that address can be forwarded only to the interface where that address is located. (Packets destined for unrecognized addresses are forwarded out every bridge interface.) MAC address learning, defined in the IEEE 802.1 standard, helps minimize traffic on the attached LANs.
Address Resolution Protocol
Switches use Address Resolution Protocol (ARP) to learn the MAC addresses of devices on the network. The switch sends an ARP request that contains the IP address of a device, and receives the MAC address for that device in an ARP reply. These dynamically learned entries are stored in the ARP cache. You can also manually configure MAC addresses, which are called static entries.
Dynamic and static ARP entries in the ARP cache resemble the following:
Console# show arp
ARP Cache Timeout: 1200 (seconds)
 
IP Address MAC Address Type Interface
--------------- ----------------- --------- -----------
192.168.0.2 74-8E-F8-68-02-30 other VLAN1
192.168.0.9 11-22-33-44-55-66 static VLAN1
192.168.0.99 00-E0-29-94-34-64 dynamic VLAN1
 
Total entry : 3
ARP age
The ARP age is the amount of time the device keeps a learned MAC address in the ARP cache. The device resets the timer to zero each time the ARP entry is refreshed and removes the entry if the timer reaches the ARP age. The default ARP age is 20 minutes.
Changing the ARP aging period
When the switch places an entry in the ARP cache, it also starts an aging timer for the entry. The aging timer ensures that the ARP cache does not retain learned entries that are no longer valid. An entry can become invalid when the device with the MAC address of the entry is no longer on the network.
ARP age affects dynamic entries only.
MAC address learning show commands
The following command displays information about the MAC address table.
show mac-address-table
Syntax:
show mac-address-table
This command displays the MAC address table, which contains MAC addresses learned from other devices. This table does not contain the MAC addresses of the Brocade device ports.
Console# show mac-address-table
 
Total entry in system: 3
Interface MAC Address VLAN Type Life Time
--------- ----------------- ---- -------- -----------------
CPU 70-72-CF-32-DD-FD 1 CPU Delete on Reset
Eth 1/ 1 00-01-EC-F8-D8-D6 1 Learn Delete on Timeout
Eth 1/ 1 00-E0-29-94-34-64 1 Learn Delete on Timeout
MAC address learning debug commands
The following command displays information about the MAC address table.
debug hardware dev-amtrdrv
Syntax:
debug hardware dev-amtrdrv {mac-table | vidx-table}
mac-table - Displays all MAC address entries.
vidx-table - Displays all multicast entries.
This command shows all MAC entries maintained by the address table management driver (operating in the system ASIC).
Console#debug hardware dev-amtrdrv mac-table
 
MAC Vid Unit/Port IsTrunk TrunkId Is_Static age_flag Idx
----------------- ---- --------- ------- ------- --------- -------- -----
74-8E-F8-68-02-30 1 1/2 0 0 1 0 40
00-E0-29-94-34-64 1 1/1 0 0 0 1 41
00-E0-0C-10-90-07 1 1/1 0 0 0 1 3108
00-E0-0C-10-90-00 1 1/1 0 0 0 1 13348
4 records
 
The following command displays detailed information about the VLAN mapping table.
Console#debug hardware dev-amtrdrv vidx-table
 
vidx vlan MAC Used
---- ---- ----------------- ----
0 1 01-00-5E-01-01-01 1
1 5 01-00-5E-02-01-01 1
2 5 01-00-5E-02-01-02 1
3 5 01-00-5E-02-01-03 1
4 5 01-00-5E-02-01-04 1
5 5 01-00-5E-02-01-05 1

Layer 2 Protocol Diagnostics : MAC address learning