WLC – Manage the Layer 2 Forwarding Database

Manage the Layer 2 Forwarding Database,An MX uses a Layer 2 forwarding database (FDB) to forward traffic within a VLAN. The entries in the forwarding database map MAC addresses to the physical or virtual ports connected to those MAC addresses within a particular VLAN. To forward a packet to another device in a VLAN, the MX searches the forwarding database for the destination MAC address of the packet, then forwards the packet to the port associated with the MAC address.

Types of Forwarding Database Entries

The forwarding database can contain the following types of entries:

• Dynamic—A dynamic entry is a temporary entry that remains in the database only until the entry is no longer used. By default, a dynamic entry ages out if it remains unused for 300 seconds (5 minutes). All dynamic entries are removed if the MX is powered down or rebooted.

• Static—A static entry does not age out, regardless of how often the entry is used. And, like dynamic entries, static entries are removed if the MX is powered down or rebooted.

• Permanent—A permanent entry does not age out, regardless of how often the entry is used. In addition, a permanent entry remains in the forwarding database even following a reboot or power cycle.

How Entries Are Added to the Forwarding Database

An entry is added to the forwarding database in one of the following ways:

• Learned from traffic received by the MX —When the MX receives a packet, the MX adds the packet source MAC address to the forwarding database if the database does not already contain an entry for that MAC address.

• Added by the system administrator—You can add static and permanent unicast entries to the forwarding database. (You cannot add a multicast or broadcast address as a permanent or static forwarding database entry.)

• Added by the MX—For example, the authentication protocols can add entries for wired and wireless authentication users. The MX also adds any static entries added by the system administrator and saved in the configuration file.

Displaying Forwarding Database Information

You can display the forwarding database size and the entries contained in the database.

Displaying the Size of the Forwarding Database

To display the number of entries contained in the forwarding database, use the following command:

show fdb count {perm | static | dynamic} [vlan vlan-id]

For example, to display the number of dynamic entries that the forwarding database contains, type the following command:

MX# show fdb count dynamic
Total Matching Entries = 2

Displaying Forwarding Database Entries

To display the entries in the forwarding database, use either of the following commands:

show fdb [mac-addr-glob [vlan vlan-id]]

show fdb {perm | static | dynamic | system | all} [port port-list | vlan vlan-id]

The mac-addr-glob parameter can be an individual address, or a portion of an address with the asterisk (*) wildcard character representing from 1 to 5 bytes. The wildcard allows the parameter to indicate a list of MAC addresses that match all the characters except the asterisk.

Use a colon between each byte in the address (for example, 11:22:33:aa:bb:cc or 11:22:33:*). You can enter the asterisk (*) at the beginning or end of the address as a wildcard, on any byte boundary.

To display all entries in the forwarding database, type the following command:

MX# show fdb all
* = Static Entry. + = Permanent Entry. # = System Entry.
VLAN TAG Dest MAC/Route Des [CoS] Destination Ports [Protocol Type]
---- ---- ------------------ ----- -----------------------------------------
1         00:01:97:13:0b:1f 1 [ALL]
1 aa:bb:cc:dd:ee:ff * 3 [ALL]
1 00:0b:0e:02:76:f5 1 [ALL]
Total Matching FDB Entries Displayed = 3

Adding an Entry to the Forwarding Database

To add an entry to the forwarding database, use the following command:
set fdb {perm | static} mac-addr port port-list vlan vlan-id [tag tag-value]
To add a permanent entry for MAC address 00:bb:cc:dd:ee:ff on ports 3 and 5 in VLAN blue, type the following command:

MX# set fdb perm 00:bb:cc:dd:ee:ff port 3,5 vlan blue
success: change accepted.

To add a static entry for MAC address 00:2b:3c:4d:5e:6f on port 1 in the default VLAN, type the following command:

MX# set fdb static 00:2b:3c:4d:5e:6f port 1 vlan default
success: change accepted.

Removing Entries from the Forwarding Database

To remove an entry from the forwarding database, use the following command:

clear fdb {perm | static | dynamic | port port-list} [vlan vlan-id] [tag tag-value]

To clear all dynamic forwarding database entries that match all VLANs, type the following command:

MX# clear fdb dynamic
success: change accepted.

To clear all dynamic forwarding database entries that match ports 3 and 5, type the following command:

MX# clear fdb port 3,5
success: change accepted.

Configuring the Aging Timeout Period

The aging timeout period specifies how long a dynamic entry can remain unused before the software removes the entry from the database.

You can change the aging timeout period on an individual VLAN basis. You can change the timeout period to a value from 0 through 1,000,000 seconds. The default aging timeout period is 300 seconds (5 minutes). If you change the timeout period to 0, aging is disabled.

Displaying the Aging Timeout Period

To display the current setting of the aging timeout period, use the following command:

show fdb agingtime [vlan vlan-id]

For example, to display the aging timeout period for all configured VLANs, type the following command:

MX# show fdb agingtime
VLAN 2 aging time = 300 sec
VLAN 1 aging time = 300 sec
Configuring and Managing Ports and VLANs
Port and VLAN Configuration Scenario
Configuring and Managing Ports and VLANs 7 – 21

Changing the Aging Timeout Period

To change the aging timeout period, use the following command:

set fdb agingtime vlan-id age seconds

For example, to set the aging timeout period for VLAN 2 to 600 seconds, type the following command:

MX# set fdb agingtime 2 age 600
success: change accepted.