Layer 2 and Layer 3 services can be commonly implemented within the same EVPN domain, as can multihoming. In this condition, for Layer 3 interfaces multi-homed to the same CE, we may encounter a situation where Layer 2 hashes ARP/ND requests to a single multihomed PE, leaving the other PE’s ARP/ND table empty. A device with an empty ARP/ND table will drop traffic, disrupting load balancing. draft-ietf-bess-evpn-l3mh-proto introduces the solution for it. The solution synchronizes ARP/ND, multicast state, and IGP routes between redundant PEs without requiring Layer 2 constructs or proprietary Inter-Chassis Communication protocols.
We tested the ARP/ND sync function in section 3.6. We simulated four subnets, two on each end, including both IPv4 and IPv6. And we sent ARP and ND from all hosts and verified that ARP and ND entries were synced with EVPN RT-2. Both multihomed PEs had identical ARP and ND entries, including both local dynamic entries and EVPN-synched entries. We then sent bidirectional unicast traffic with Keysight IxNetwork and observed no packet loss and proper load balancing.