A customer is concerned about me unprotected traffic between an AOS-CX switch and a gateway,...

According to the Aruba Documentation Portal1, PAPI (Port Aggregation Protocol) is a protocol that allows multiple physical ports to be aggregated into a single logical port for increased bandwidth and performance. PAPI can be used between AOS-CX switches and gateways, or between AOS-CX switches and other devices.

Option A: Implement an IPSec tunnel to protect PAPI between the AOS-CX switches and the gateway

This is because option A shows how to implement an IPSec tunnel between two devices using the interface command and the ipsec command. An IPSec tunnel can provide encryption and authentication for PAPI traffic between two devices, such as an AOS-CX switch and a gateway2.

Therefore, option A is a feasible option to protect this traffic.

I hope this helps you. If you need more information, please let me know. ????

1: https://www.arubanetworks.com/techdocs/AOS-CX/10.06/HTML/5200-7727/Content/Chp_prev_traf_loss/Act_gtw_act_fwd/act-gat-ove-vsx-10.htm  2: https://community.arubanetworks.com/blogviewer?blogkey=989fc43a-e0df-42db-9c0b-f96d6565a1fa