Forcing a Port Up in a Basic MCT Configuration

In a dynamic LAG environment, Preboot eXecution Environment (PXE) images are too small for most operating systems to leverage LACP during the boot process. As a result, during a PXE build process, traffic sent by the server is dropped, and the build process can fail.

To correct this situation, a port on the supported ICX device connected to a server that is configured as an MCT client can be set to a “force-up” state so that even if the LACPDU is not received from the server, the connected port is up and forwards packets.

Note: When multiple ports from the same server are connected to the ICX device, the port on the ICX device connected to the PXE-capable port on the server is the port that must be configured to the force-up state. The PXE-capable port varies from server to server.

Keep the following points in mind when configuring a port to a force-up state:

  • A port can only be configured as the force-up port before the client is deployed.
  • Only one port in an LACP link aggregation group (LAG) can be configured as the force-up port. If you configure multiple ports as force-up, the following error message is displayed: Error: port portno is already configured as force-up port.
  • When a port is configured for force-up and the server boots for the first time, the port does not wait for any LACPDU but immediately begins to forward packets.
  • If the port receives an LACPDU, it bundles with other ports and forms a LAG. The server is operational.
  • If the force-up port goes down while in a LAG, the port continues to perform as a normal LACP trunk, and the server remains operational, with some ports down.
  • If the force-up port stops receiving LACPDUs, the port ignores the time-out and remains operational.
  1. To configure the LACP client in a force-up state, use the client-interface link-aggregation force-up ethernet command at the client level.

The following example shows output from the show lag command after the link aggregation information for a port has been configured in a force-up state. 

Router# show lag id 163

Total number of LAGs:          11
Total number of deployed LAGs: 11
Total number of trunks created:11 (113 available)
LACP System Priority / ID:     1 / 748e.f88f.2222
LACP Long timeout:             90, default: 90
LACP Short timeout:            3, default: 3

=== LAG "CCEP-163" ID 163 (dynamic Deployed) ===
LAG Configuration:
   Ports:         e 1/1/47 to 1/1/48 
   Port Count:    2
   LAG Interface: lg163
   Trunk Type:    hash-based
   LACP Key:      20163
Deployment: HW Trunk ID 3
This is a Multi Chassis Trunk: (System Id: 0180.c200.0001, Key: 30163)

Port    Link    State   Dupl Speed Trunk Tag Pvid Pri MAC             Name
1/1/47  Up      Forward Full 1G    163   Yes N/A  0   748e.f88f.2222            
1/1/48  Down    None    None None  163   Yes N/A  0   748e.f88f.2222            

Port   [Sys P] [Port P] [ Key ] [Act][Tio][Agg][Syn][Col][Dis][Def][Exp][Ope]
1/1/47       1        1   20163   Yes   L   Agg  Syn  Col  Dis  Def  No   Frc
1/1/48       1        1   20163   Yes   L   Agg  Syn  No   No   Def  No   Dwn


 Partner Info and PDU Statistics 
Port       Partner         Partner     LACP      LACP     
          System MAC         Key     Rx Count  Tx Count  
1/1/47    0000.0000.0000       46     5475      5558
1/1/48    0000.0000.0000       47     5477      5487

Parent topic: Basic MCT Configuration