Description

This article explains the automatically generated logical units for physical interfaces in Junos.

Symptoms

Consider a newly deployed router: 

lab@MX> show interfaces terse
xe-0/0/2                up    up
xe-0/0/2.16386          up    up
xe-0/0/3                up    down
xe-0/0/3.16386          up    down
This is the behavior of an interface configured for logical units with VLAN tagging: 
# set interfaces xe-0/0/2 vlan-tagging unit 2 vlan-id 222
> show interfaces terse
xe-0/0/2                up    up
xe-0/0/2.2              up    up   multiservice
xe-0/0/2.32767          up    up   multiservice

Solution

Logical units 16386 and 32767 are created by Junos to accept untagged packets that come in the interface.

Unit 16386 is created on 10G and 40G interfaces when a SFP module is inserted without any logical unit (IFL) configuration.

  • The default IFL, 16386, is added only when there is no other configuration on the interface.

  • The default IFL on the interfaces is to support VC auto-provisioning on (et-/xe-) interfaces.

Unit 32767 is created when an interface is configured with vlan-tagging services.

Modification History

2022-03-22: slight modification to first list item in the solution section.