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With the distributed ARP mode enabled, L3 routed packets get dropped on egress LAG ports

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TitleWith the distributed ARP mode enabled, L3 routed packets get dropped on egress LAG ports
Symptoms
In this scenario, the distributed ARP mode is enabled on the BD8K, and the egress VLAN (V200) has two LAG ports (1:2/2:2 and 1:3/2:3). 
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When one LAG port has a member port (1:2) active on the ingress chip but the other LAG port has a member port (2:3) active on the different chip/module, the packets being routed from the ingress chip to the egress chip get dropped.
Environment
  • EXOS All (BD8K and BDX8)
Cause
In the distributed ARP mode, the L3 lookup takes place on the egress chip to reduce the utilization of the next-hop hardware entries in order to achieve higher ARP scale. 
(Without the distributed ARP mode, the ingress chip does the L3 lookup and routes the packets out a front-panel port on the egress chip/module.)

When the ARP is on a LAG port, and no member ports are on the ingress chip, the ARP can be distributed using a special egress port ID representing the egress chip, so the packet is sent unmodified to the egress chips for L3 lookup.

However, in the case that both LAG ports have any of their member ports on the ingress chip, and one LAG port has member ports active on the ingress chip but the other LAG port has member ports active on the different chip, the ingress chip is not capable of supporting both local and remote L3 lookup for the two egress LAG ports at the same time due to the hardware limitation.  
Resolution
Our recommendation is not to have more than two LAG ports in the egress L3 VLAN or disable the distributed ARP mode when multiple egress LAG ports have any of their member ports on the ingress chip.

xos0063161: BDX & BD8K With "distributed ARP-mode + LAG" packets dropped across unit
Additional notes
In the configuration where the ingress ports and egress LAG member ports are on different chips/modules, the switch with the distributed ARP mode enabled is not affected by this limitation.

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