l3fwd, as it's name suggests, uses L3 headers to make forwarding decisions.
The L3 protocols it supports are IPv4 and IPv6. This software is not suited for
handling other types of protocols, such as ARP, which is not strictly L3 or
EtherCAT which is L2. If you wish to handle other types of protocols, you
probably need to look at different DPDK applications or even create your own
from scratch. Everything depends on how you actually want to handle your ingress
egress traffic. If the task is just to make the node transparent to ARP,
you can take a look at l2fwd. As of EtherCAT, there is no support to it in
DPDK or LSDK at all.
Best Regards,
Platon