This articles explains a situation in which a microkernel core can be seen for MPC linecards on Juniper MX devices because "mixed-rate AE bundles" and "adaptive load balancing" are both configured for the Aggregated Ethernet (AE) bundle.

On devices that run earlier Junos OS versions (before and including Junos OS Release 16.1R2-S2), the Command Line Interface (CLI) has an option to configure both mixed-rate and adaptive load-balancing for AE bundles. 

Mixed-rate is used to enable member links with different speeds to be a part of the AE bundle, whereas adaptive load balancing allows the load sharing to be more equitable over the member links by using a feedback mechanism.

• Mixed-rate: See Aggregated Ethernet Interfaces .

• Adaptive load balancing: See Load Balancing on Aggregated Ethernet Interfaces .

Configuring both these together is counter-intuitive and should be avoided. When both configurations are in place for the AE bundle, which has member interfaces on MPC linecards, it can lead to excessive route churns and in turn might lead to FPC crash with microkernel core generation.

Use either of the two: either mixed-rate AE bundle or adaptive load balancing. On later Junos OS versions, the CLI does not allow the two to be configured together: 

Example

​root@test-re0# set interfaces ae1 aggregated-ether-options link-speed mixed
root@test-re0# set interfaces ae1 aggregated-ether-options load-balance adaptive

root@test-re0# commit and-quit
re0:
[edit interfaces ae1 aggregated-ether-options load-balance]
  'adaptive'
    load-balance adaptive is incompatible with link-speed mixed
[edit interfaces ae1 aggregated-ether-options link-speed]
  'link-speed mixed'
    Mixed-rate AE is not supported along with Adaptive Load balance mode
error: commit failed: (statements constraint check failed)