Link Aggregation Control Protocol (LACP) Fallback Option

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 feature 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:

Supported Platforms

Summit X450-G2, X460-G2, X670-G2, X770, and ExtremeSwitching X620, X440-G2 series switches

Limitations

When using LACP fallback with MLAG, fallback port is selected only on the LACP master.

New CLI Commands

configure sharing port lacp fallback [enable | disable]

Changed CLI Commands

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