---
title: ecn_synack_lost
framework: Kernel
role: symbol
role_heading: Instance Property
platforms: [macOS 13.0+]
path: kernel/if_tcp_ecn_stat/3944040-ecn_synack_lost
---

# ecn_synack_lost

## Declaration

```occ
u_int64_t ecn_synack_lost;
```