VSX LAG is a feature that allows a pair of Aruba CX switches to form a multichassis LAG with a downstream or upstream device. VSX LAG provides link redundancy and load balancing across the two switches. Outgoing traffic from the VSX pair to the peer device is switched to a port based on a hashing algorithm that considers various parameters such as source and destination MAC addresses, IP addresses, ports, etc. The hashing algorithm may select a port that belongs to either switch in the pair, depending on the traffic characteristics1. However, outgoing traffic is preferentially switched to local members of the LAG, meaning that each switch tries to use its own ports first before using the ISL link to send traffic to the other switch's ports2. This reduces the ISL utilization and improves performance.
References:
1
https://www.arubanetworks.com/techdocs/AOS-CX/10.07/HTML/5200-7888/Content/VSX_cmds/int-lag- mul-c
https://www.arubanetworks.com/techdocs/AOS-CX/10.07/HTML/5200-7888/Content/Chp_Start/vsx-lag-
10.11.