The desc explicitly states this is the count of IPsec ESP encrypted packets — packets encrypted using plain, non-UDP-encapsulated ESP, the standard mode for site-to-site VPN traffic not behind NAT. This is the main-line VPN encryption packet counter for most site-to-site deployments and should track cpvEncPackets closely, since cpvEncPackets is the higher-level total that this ESP-specific counter mostly comprises on a modern IPsec-only gateway. e.g. cpvIpsecEspEncPkts and cpvEncPackets both growing at essentially the same rate, confirming ESP is the encryption mechanism actually carrying nearly all of this gateway's VPN traffic.