This article describes a mac/arp learning issue on QFX5100/QFX5110/EX4600 platforms. 
If copper base SFP-T is used, interfaces might not come up/up on physical layer and the MAC/ARP learning might not even work if the interface does come up.

For example:

root> show interfaces terse ge-2/0/24 
Interface               Admin Link Proto    Local                 Remote
ge-2/0/24               up    up
ge-2/0/24.0             up    up   inet     192.168.0.1/24


root> ping 192.168.0.2 source 192.168.0.1    
ping: bind: Can't assign requested address

• Use 1G SPF optic interface as a workaround.
• Upgrade to the listed versions in this PR for a permanent fix: 
  https://prsearch.juniper.net/problemreport/PR1437577

2023-11-03 : Article Created
2025-03-06 : Minor changes to formatting, appearance and text.