SDWAN packet overhead for ESP

IPSec-Encrypted Cisco SD-WAN Overlay (default)
IPSec ESP header: 20 bytes (can be higher depending on options)
UDP header: 8 bytes
Outer IP header (IPv4): 20 bytes
SD-WAN metadata (vSmart control, segmentation, etc.): ~28 bytes (can vary)
Total overhead: ~76 bytes