Introduction

If the local LAG interface cannot sense self-loop or a fault occurring on the member interface of the peer LAG on the remote device in a timely manner, data will still be load balanced to the local active interfaces of the LAG, resulting in loss of data traffic on the faulty link.

To quickly detect member interface fault on the peer device, users can enable LACP fast rate by using command set protocols lacp interface <interface-name> rate <fast | slow >.

After configuring fast rate, the period of sending LACP PDUs from the peer member interface is 1 second. If local member interface does not receive LACP PDU from the peer interface within 3 seconds (3 times the rate), the peer member interface will be considered unreachable and the status of the local member interface will be changed to Down immediately, and no more data will be forwarded through this interface.

By default, the rate mode is slow, the period of receiving LACP PDUs from the peer member interface is 30 seconds. The timeout period for changing local interface status to Down is 90 seconds.

When the local switch configures LACP fast rate, it forces the peer switch to start sending LACP PDU at a faster rate. It is allowed to have two peers with different LACP rate settings.

Configuring LACP Fast Rate

Procedure

• Use the following command to configure LACP fast rate.

   set protocols lacp interface <interface-name> rate <fast | slow>

   The default value is slow.

Configuration Example

Figure 1. Configuring LACP Link Aggregation Fast Rate Networking Diagram

Switch A and Switch B are both connected to VLAN 10 and VLAN 20 respectively via Ethernet links, and suppose there is a large amount of data traffic between Switch A and Switch B.

• To improve link bandwidth and reliability, LACP mode link aggregation groups are configured on the link between the two switches.
• To quickly detect peer member interface fault, LACP fast rate is enabled on the member interfaces on both switches.

Switch A

Step 1        Configure the LAG interface.

admin@SwitchA# set vlans vlan-id 10
admin@SwitchA# set vlans vlan-id 20
admin@SwitchA# set interface aggregate-ethernet ae1 aggregated-ether-options lacp enable true
admin@SwitchA# set interface gigabit-ethernet te-1/1/1 ether-options 802.3ad ae1
admin@SwitchA# set interface gigabit-ethernet te-1/1/2 ether-options 802.3ad ae1
admin@SwitchA# set interface aggregate-ethernet ae1 family ethernet-switching port-mode trunk
admin@SwitchA# set interface aggregate-ethernet ae1 family ethernet-switching native-vlan-id 10
admin@SwitchA# set interface aggregate-ethernet ae1 family ethernet-switching vlan members 20

Step 2        Configure LACP fast rate.

admin@SwitchA# set protocols lacp interface te-1/1/2 rate fast

Step 3        Commit the configuration.

admin@SwitchA# commit

Switch B

Step 1        Configure the LAG interface.

admin@SwitchB# set vlans vlan-id 10
admin@SwitchB# set vlans vlan-id 20
admin@SwitchB# set interface aggregate-ethernet ae1 aggregated-ether-options lacp enable true
admin@SwitchB# set interface gigabit-ethernet te-1/1/1 ether-options 802.3ad ae1
admin@SwitchB# set interface gigabit-ethernet te-1/1/2 ether-options 802.3ad ae1
admin@SwitchB# set interface aggregate-ethernet ae1 family ethernet-switching port-mode trunk
admin@SwitchB# set interface aggregate-ethernet ae1 family ethernet-switching native-vlan-id 10
admin@SwitchB# set interface aggregate-ethernet ae1 family ethernet-switching vlan members 20

Step 2        Configure LACP fast rate.

admin@SwitchB# set protocols lacp interface te-1/1/2 rate fast

Step 3        Commit the configuration.

admin@SwitchB# commit

Verify the Configuration

• After completing the configuration, check the rate mode by using command run show lacp internal command.

admin@SwitchB# run show lacp internal
Aggregated interface: ae1
Port Number    System ID                Priority   Admin Key   Oper Key   State   Receive State  Transmit State    Mux State
-----------    ------------------------ --------   ---------   --------   -----   -------------  --------------    -------------------------
te-1/1/1      32768,48:6E:73:FF:00:FF   32768      0x203       0x203      0x3F    Current        Slow Periodic     Collecting Distributing

te-1/1/2      32768,48:6E:73:FF:00:FF   32768      0x203       0x203      0x3F    Current        Fast Periodic     Collecting Distributing 

Users can check the fast/slow rate from the column “Transmit State “. The value could be "Fast Periodic" or "Slow Periodic", indicating the rate at which the local switch interface is sending LACP PDUs. This value is controlled by the peer switch using command set protocols lacp interface <interface-name> rate <fast | slow >.