An ESI-LAG between a Juniper ACX7348 and a Cisco ASR99XX won't come up. Downsteam LACP speaker is an optical line termination (OLT) device.

The following configuration is used on Juniper ACX7348:

set interfaces et-0/0/32 description "to data center"

set interfaces et-0/0/32 speed 10g

set interfaces et-0/0/32 ether-options 802.3ad ae50

set interfaces ae50 flexible-vlan-tagging

set interfaces ae50 encapsulation flexible-ethernet-services

set interfaces ae50 esi 00:01:18:00:bd:18:30:54:00:32

set interfaces ae50 esi single-active

set interfaces ae50 aggregated-ether-options lacp active

set interfaces ae50 aggregated-ether-options lacp system-id 02:00:00:00:00:30

set interfaces ae50 unit 999 encapsulation vlan-bridge

set interfaces ae50 unit 999 vlan-id 999

set routing-instances 1068 instance-type mac-vrf

set routing-instances 1068 protocols evpn

set routing-instances 1068 service-type vlan-based

set routing-instances 1068 route-distinguisher 65534:1068

set routing-instances 1068 vrf-target target:65534:1068

set routing-instances 1068 vlans vlan999 vlan-id 999

set routing-instances 1068 vlans vlan999 interface ae50.999

set routing-instances 1068 vlans vlan999 l3-interface irb.9845

Output from the OLT downstream:

ethernet 1 1 x2

  port-state               unbundled

  lacp-fault-on-port-alarm set

   lacp-fault-on-port-reason partner-key-mismatch

  rx-state                 defaulted

  tx-state                 fast-periodic

  mux-state                detached

When both devices are enabled, Cisco device is working and Juniper is not:

ethernet 1 1 x1 (cisco)

   port-number    50

   port-priority  32768

   system-id      02:00:00:00:00:30

   system-priority 32768

    key            50

ethernet 1 1 x2 (Juniper)

   port-number    0

   port-priority  0

   system-id      00:00:00:00:00:00

   system-priority 32768

    key            0

Shut down the Cisco port facing the OLT and see this on ethernet 1 1 x2 (ACX):

   port-number    2

   port-priority  127

   system-id      02:00:00:00:00:30

   system-priority 127

    key            51

System-ID must be the same on each PE, as well as the admin-key:

# set interfaces ae50 aggregated-ether-options lacp admin-key 50

"For Multichassis Link Aggregation (MC-LAG), you must specify the system-id and admin key. MC-LAG peers use the same system-id while sending the LACP messages."

https://www.juniper.net/documentation/us/en/software/junos/fusion-enterprise/topics/task/interfaces-configuring-aggregated-ethernet-lacp-l2.html