Hi Folks,
What is this platform?
Are you looking for e0 or em0?
If em0 and the platform is MX or SRX or T-series then,
https://www.juniper.net/techpubs/en_US/junos16.1/topics/task/troubleshooting/interfaces-em0-down-troubleshooting.html
https://kb.juniper.net/InfoCenter/index?page=content&id=KB21706&actp=search
https://kb.juniper.net/InfoCenter/index?page=content&id=KB27820&actp=search