Usually, in an MC-LAG configured environment, "MAC addresses learned on an MC-LAG of one MC-LAG peer must be replicated as learned on the same MC-LAG of the other MC-LAG peer. MAC addresses learned on single-homed customer edge (CE) clients of one MC-LAG peer must be replicated as learned on the ICL interface of the other MC-LAG peer." ( Multichassis Link Aggregation Features, Terms, and Best Practices )

However, sometimes there are some VLANs which are NOT members of any MC-LAG configured interfaces. This article describes how those VLANs should be configured and discusses a known limitation.

Assume that the following MC-LAG configured for vlan 1-99 has been configured and is running normally;

set interfaces ae1 description ICL-LINK
set interfaces ae1 aggregated-ether-options lacp active
set interfaces ae1 aggregated-ether-options lacp periodic fast
set interfaces ae1 unit 0 family ethernet-switching interface-mode trunk
set interfaces ae1 unit 0 family ethernet-switching vlan members 1-99

There are two additional scenarios:

Scenario A: A vlan (vlan200) is a member of one or multiple MC-LAG interface and also a member of a single-homed interface
Scenario B: A vlan (vlan300) is a member of a single-home interface only. It is NOT a member of any MC-LAG interface.

The Solution discusses how the ICL in each of these scenarios should be configured.

Scenario A:

Since vlan200 is a member of MC-LAG ae2, it must be added to ICL. ICCP/ICL should be the MAC learning mechanism in this case.

set interfaces ae2 unit 0 family ethernet-switching vlan members 200  ; ae2 is an MC-LAG interface. vlan 200 is newly added
set interfaces ae1 unit 0 family ethernet-switching vlan members 1-99 ; existing configuraiton
set interfaces ae1 unit 0 family ethernet-switching vlan members 200  ; vlan 200 is newly added into the ICL

Limitation:

When a VLAN is a member of MC-LAG, it is NOT recommended to add a new interface linked between two switch devices. The MAC learning of the VLAN is processed on the new interface link.

As an example, NEITHER configuration below should be deployed

(i)  set interfaces ae1 unit 200 family ethernet-switching vlan members 200
(ii) set interfaces ge-0/0/10 unit 200 family ethernet-switching vlan members 200 

Scenario B:

1. Add a new interface linked between two Switch devices

    set interfaces ge-0/0/10 unit 300 family ethernet-switching vlan members 300

2. Add the vlan300 into an existing MC-LAG interaface or create a new MC-LAG interface which has vlan300 as a member VLAN. Then add the vlan300 into the ICL.

    set interfaces ae2 unit 0 family ethernet-switching vlan members 300 ; ae2 is an MC-LAG interface
    set interfaces ae1 unit 0 family ethernet-switching vlan members 300 ; ae1 is ICL interface

• Multichassis Link Aggregation Features, Terms, and Best Practices