In my JunOS configure mode, I show the interfaces:

root@Olive# show interfaces
em0 {
    unit 0 {
        family inet {
em1 {
em2 {
em3 {

What's the meaning of unit 0 and family inet?

1 Answer 1


A physical interface can consists of multiple logical interfaces, each called a unit. Each unit has a number as a unique identifier. The 0 just refers to the first logical interface.

It's good practice (but not required) to keep the unit number in sync with the VLAN id. In that case unit 0 often refers to the untagged interface.

family inet refers to the IPv4 address family. An interface can have configuration for multiple address families, each with their own specific configuration and purpose.

  • Teun, you might want to swap physical and logical in the first sentence... ;-)
    – Zac67
    Jul 27, 2018 at 12:16
  • eh, why exactly? I don't see anything wrong in how I described this. Units are logical interfaces.
    – Teun Vink
    Jul 27, 2018 at 12:35
  • I think you mean "a logical interface can consist of multiple physical interfaces". The other way around you've got to show me. ;-D
    – Zac67
    Jul 27, 2018 at 15:56

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