By default, when an ESX/ESXi host communicates with any destination server on another subnet, it communicates through its default gateway router.
If the traffic sent to the default gateway router is destined to be forwarded by that router to another router on the same subnet, the default gateway reply to the ESX/ESXi host with an Internet Control Management Protocol (ICMP) Redirect message.
The purpose of this ICMP Redirect message is to tell ESX/ESXi that there is a better route to the destination host and it must instead communicate with the other router.
This article provides steps to view the ICMP Redirect route table.