After migrating a Unified Storage Router (USR) connection from a Cisco access port to a Juniper QFX5120 VXLAN/EVPN leaf, the physical link comes up but the QFX does not learn the USR MAC address on the attached interface. Moving the USR back to the Cisco switch restores normal behavior and MAC learning.

• QFX interface shows up/up, but no USR MAC entries appear in the switching/MAC table for the expected VLAN.
• Monitor traffic on the QFX port shows no USR user traffic (no ARP/IPv4 or IPv6/NDP frames), at most segment/control traffic (e.g., IGMP queries, LLDP).
• QFX-side PCAP confirms no frames sourced from the USR MAC during the test window.
• Cisco-side capture may show IPv6 control traffic (ICMPv6/NDP), but the same traffic is not observed when the USR is connected to the QFX.

Recommended troubleshooting steps

1- Confirm the USR is actually transmitting on the Juniper attachment

• Start a capture (SPAN/analyzer/pcap) and bounce the USR link.
• Immediately force traffic from the USR (ping its gateway; if IPv6 is enabled, ping6 to trigger NDP).

2- Capture only relevant traffic on the QFX port

Run on the QFX while traffic is being generated:

• monitor traffic interface <int> no-resolve layer2-headers matching "0x0806|0x0800|0x86dd|arp|icmp" size 1500

Validate whether ARP (IPv4), IPv4, or IPv6 frames are actually ingressing the interface.

3- If no USR frames are seen on the QFX capture

• The issue is upstream of MAC learning: the switch can’t learn a MAC if it’s not receiving frames from the endpoint.
• Investigate USR interface/NIC settings (link negotiation, teaming/bonding behavior, VLAN expectations), optics/cabling, and any intermediate patching between the USR and the QFX.

4- Optional: take a full PCAP via analyzer/SPAN

• If an analyzer is configured to mirror ingress/egress of the USR port to another interface, take a PCAP on the mirror destination to confirm traffic presence and tagging.