This article outlines an issue observed on EX4300 switches, where enabling MAC limiting features such as mac-move-limit or interface-mac-limit may prevent the switch from forwarding packets used for MAC address learning.

Packet drops may occur when MAC limiting features are enabled.

Enabling MAC limiting features changes MAC address learning from hardware-based to software-based processing.

On version 21.4R3-S10, enabling MAC limiting features causes ARP requests received on built-in ports to not be forwarded during software-based source MAC (SMAC) learning. ARP requests received on uplink ports, along with other packet types such as ICMP, UDP, TCP, and ARP replies, are not dropped when received on any port used for software-based SMAC learning. However, on older releases such as 18.4R2-S7, all packets (including ARP requests/responses, ICMP, UDP, etc.) received on any port that triggers software SMAC learning are dropped. 

Note: This issue affects only packets used for MAC learning. All subsequent packets are processed correctly.

Workaround: Disable MAC Limiting features - mac-move-limit and interface-mac-limit.

The issue with ARP requests received on built-in ports, which are not forwarded during SMAC learning in 21.4R3-S10, is being addressed in PR 1873052, in 21.4R3-S11.