Discussion

unit 0 {
family inet {
address 172.19.121.3/24;
}
}
While you can set the ge-1/1/0 interface configuration without issuing the
deactivate command, you are leaving yourself open for possible problems if someone
installs the PIC unexpectedly.
Deactivating an interface’s configuration rather than deleting is also a good practice
when the hardware fails and you are waiting for a replacement PIC. When the new
PIC arrives, you don’t need to reconfigure the interface. Just reactivate it:
[edit interfaces]
aviva@router1# activate ge-1/1/0
For all interfaces, you can configure a disable statement. While this might look like a
way to deactivate an interface, it actually does something quite different: it activates
the interface, but treats it as being down or administratively disabled. When you
commit a configuration that contains a disabled interface, the interface control daemon,
DCD, sees the interface and the configuration data, but does not configure the
interface. Here, you disable interface fe-0/0/0:
[edit interfaces]
aviva@router1# set fe-0/0/0 disable
The configuration shows this:
[edit interfaces]
aviva@router1# show fe-0/0/0
disable;
unit 0 {
family inet {
address 192.168.20.1/30;
{
}
When you check the status of the interface, you see that the physical interface is
administratively down, but the link to the remote side is up. The logical interface is
also down.
aviva@router1> show interfaces fe-0/0/0 terse
Interface Admin Link Proto Local Remote
fe-0/0/0
down up
fe-0/0/0.0 up down inet 192.168.20.1/30
This output illustrates that when an interface is disabled instead of being deactivated,
you see information about the interface in the show interfaces output instead
of seeing nothing at all, which is the case with the deactivated interface.
To get the interface back up, you might think that it’s logical to enable it:
[edit interfaces fe-0/0/0]
aviva@router1# set enable
244 | Chapter 7: Router Interfaces
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