Preboot Execution Environment (PXE) is an industry standard client/server environment that allows workstations to boot from the server before their full operating system is up and running. PXE images are too small to take advantage of Link Aggregation Control Protocol (LACP) functionality, and therefore it is up to the administrator to statically configure the switch for correct connectivity. This also means that after the full operating system is up and running, the switch needs to be reconfigured for LACP. The LACP Fallback option automates this process.
The LACP Fallback option lets you select a single port that is automatically added to the aggregator if LACP data units (LACPDUs) do not appear on any of the member ports within the specified period of time. If LACPDUs are exchanged before this timeout expires, an aggregator is formed using traditional means. If LACPDUs are not received, an active port with the lowest priority value is automatically added to the aggregator (enters fallback state). If ports have the same priority value, the lowest port number on the lowest slot number is chosen.
The selected port stays in the fallback state until fallback is disabled or until LACPDUs are received on any of the member ports, at which point the old aggregator is removed and a new one is selected based on information propagated in the LACPDUs. The new fallback port may also be re-elected if the existing fallback port changes its state (for example, port priority change, link bounce, port disable/enable, etc.).
The LACP fallback option configuration consists of:
When using LACP fallback with MLAG, fallback port is selected only on the LACP master.
configure sharing port lacp fallback [enable | disable]
The show lacp lag group-id detail command now shows fallback information (shown in bold):
# show lacp lag 17 detail
Lag Actor Actor Partner Partner Partner Agg Actor
Sys-Pri Key MAC Sys-Pri Key Count MAC
--------------------------------------------------------------------------------
17 0 0x03f9 00:00:00:00:00:00 0 0x0000 1 00:04:96:6d:55:13
Enabled : Yes
LAG State : Up
Unack count : 0
Wait-for-count : 0
Current timeout : Long
Activity mode : Active
Defaulted Action : Delete
Fallback : Enabled
Fallback timeout : 40 seconds
Receive state : Enabled
Transmit state : Enabled
Minimum active : 1
Selected count : 1
Standby count : 0
LAG Id flag : Yes
S.pri:0 , S.id:00:04:96:6d:55:13, K:0x03f9
T.pri:0 , T.id:00:00:00:00:00:00, L:0x0000
Port list:
Member Port Rx Sel Mux Actor Partner
Port Priority State Logic State Flags Port
--------------------------------------------------------------------------------
17 10 Initialize Unselected Detached A-G----- 0
18 5 Initialize Fallback Collect-Dist A-GSCD-- 1018
19 5 Idle Unselected Detached -------- 0
========================================================================
Actor Flags: A-Activity, T-Timeout, G-Aggregation, S-Synchronization
C-Collecting, D-Distributing, F-Defaulted, E-Expired
The show lacp member-port port detail command now shows fallback information (shown in bold):
# show lacp member-port 18 detail
Member Port Rx Sel Mux Actor Partner
Port Priority State Logic State Flags Port
--------------------------------------------------------------------------------
18 5 Initialize Fallback Collect-Dist A-GSCD-- 1018
Up : Yes
Enabled : Yes
Link State : Up
Actor Churn : False
Partner Churn : True
Ready_N : Yes
Wait pending : No
Ack pending : No
LAG Id:
S.pri:0 , S.id:00:04:96:6d:55:13, K:0x03f9, P.pri:65535, P.num:1018
T.pri:0 , T.id:00:00:00:00:00:00, L:0x0000, Q.pri:65535, Q.num:1018
Stats:
Rx - Accepted : 0
Rx - Dropped due to error in verifying PDU : 0
Rx - Dropped due to LACP not being up on this port : 0
Rx - Dropped due to matching own MAC : 0
Tx - Sent successfully : 1162
Tx - Transmit error : 0
=======================================================================
Actor Flags: A-Activity, T-Timeout, G-Aggregation, S-Synchronization
C-Collecting, D-Distributing, F-Defaulted, E-Expired