A Juniper router, when configured with aggregated ethernet, does not allow link-mode settings (speed or duplex) to be set on any of the member links. An error message occurs when attempting to commit such a configuration.

This article explains how to resolve the error.

A Juniper router does not allow any link-mode properties to be configured on an interface that is added as a member of an aggregated ethernet link. The link-mode settings are the speed or duplex settings, and are configured under the physical interface properties. For example, the following configuration output displays the link-mode setting configured for full-duplex on interface ge-0/0/0:

[edit interfaces ge-0/0/0]
root@router# show
link-mode full-duplex;
gigether-options {
    802.3ad ae0;
}

When the configuration is committed, the following error occurs:

lab@hairy-re0# commit check 
[edit interfaces ge-0/0/0 gigether-options]
  '802.3ad'
     ae child device link-mode setting is not allowed
error: configuration check-out failed

Remove all link-mode configuration settings from the member ethernet interface:

[edit interfaces ge-0/0/0]
root@router# show 
gigether-options {
802.3ad ae0;
}

The configuration can now be successfully committed:

[edit interfaces ge-0/0/0]
root@router# commit
commit complete

By default, ethernet interfaces on a Juniper router will auto-negotiate, thus allowing full-duplex operation.

2020-05-29: Article reviewed for accuracy; no changes made; article still valid