This Counter32 counts the total number of failed ESP-encrypted inbound SAs for this Virtual Interface, per its description, incrementing every time such an SA setup attempt has failed since the counter was last reset. An admin treats a rising value here as a direct signal of ESP-specific negotiation trouble on this tunnel, whether from ESP key/policy mismatches or a flapping peer. For example, an admin noticing this ESP failed-SA counter climbing on VI 9 carrying a branch-office VPN would next check the matching crypto map's ESP transform set and lifetimes against the peer's configuration.