This article provides troubleshooting steps for resolving issues when a RETH interface appears as 'Down' despite the physical interface being 'Up'

During the issue, the Reth interfaces will appear as physically down, even though the physical interfaces show as up. Below are the details of the interfaces:

root@SRX> show interfaces reth8 extensive
Physical interface: reth8, Enabled, Physical link is Down

root@SRX> show interfaces ge-7/0/6 extensive
Physical interface: ge-7/0/6, Enabled, Physical link is Up

root@SRX> show interfaces ge-7/0/7 extensive
Physical interface: ge-7/0/7, Enabled, Physical link is Up

This issue can occur for several reasons, such as:

1) If LACP is configured on the RETH interface and LACP goes down, it will cause the RETH interface to go down. To verify, run the show lacp interfaces command and check if LACP is up.

2) Another possible cause is if the physical interface from only one node is mapped to the RETH interface. If the redundancy group fails over to the other node, this can also result in the issue. To resolve this, either fail over the redundancy group to the node where the physical interface is mapped to the RETH, or configure a physical interface on both nodes and map them to the RETH interface.