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Known Limitations

Learn about known limitations in Junos OS Evolved Release 23.4X100-D20 for QFX Series switches

For the most complete and latest information about known Junos OS Evolved defects, use the Juniper Networks online Junos Problem Report Search application.

General Routing

  • When a VXLAN encapsulated IP packet, or an IP packet with UDP port matching the VXLAN UDP port, is received on a vlan-tagging enabled interface, the switch drops the frame. This issue is not seen if the incoming port is an untagged interface, or if the interface is actually doing VXLAN encap/decap operations. In such cases, the device forwards the frame correctly.PR1805922

  • IPv4 or IPv6 reserved multicast and L2 multicast traffic received over VXLAN access port is flooded out of all ports of the VXLAN except vtep. PR1811158

  • On Junos OS Evolved QFX5000 platforms when PFC watchdog configured with detection parameter as 1, there is possibility of false detection of PFC storm. This is happening due to timer design of underlying hardware. PR1824104

  • The PFC watchdog can be triggered when it is set with a very low detection timer value, like 4 ms, while continuously receiving PFC XOFF frames from the peer device. On the peer device, two different priorities have been configured for PFC. One priority has a very high PFC XON offset (greater than 10,000), while the other priority uses the default PFC XON offset (20).

    As part of the PFC feature, BCM supports a PFC refresh functionality. When a priority experiences congestion and the current buffer utilization exceeds the PFC XOFF threshold, a PFC XOFF frame is sent. If the buffer utilization does not fall back to the PFC XON threshold within the default PFC refresh time, the port will generate a new PFC XOFF refresh frame to the peer device. For a 100G port, the default refresh time is 262 microseconds. This is why multiple PFC XOFF frames may be observed before a PFC XON frame is sent.

    This behavior is expected for the priority with the higher XON offset. However, due to hardware design limitations, the PFC refresh timer operates on a per-port basis. Therefore, when the per-port PFC refresh timer expires, the port triggers PFC refresh XOFF frames for all priorities that are in the XOFF state at that time. The hardware cannot distinguish which priority's refresh timer has expired. As a result, even for a priority with the default XON offset, multiple refresh XOFF frames may be sent continuously due to the expiration of the port-level PFC refresh timer. This could cause the peer device to detect a PFC storm for that priority as well. Since this is a hardware limitation, it cannot be resolved. Aside from the continuous XOFF frames that may trigger PFC watchdog detection on the peer, there are no other functional impacts due to this design.

    The recommendation is that if a user sets a very high XON offset for any priority on a port, which could lead to PFC refresh timer expiry and continuous XOFFs, the peer device should be configured with a longer PFC watchdog detection timer. For instance, if a PFC XON offset of 10,000 is set for a priority, the peer device should have a PFC watchdog detection timer of at least 10 ms. PR1833562