---
title: iff_output_func
framework: Kernel
role: symbol
role_heading: Type Alias
platforms: [macOS 10.4+]
path: kernel/iff_output_func
---

# iff_output_func

## Declaration

```occ
typedef errno_t (*iff_output_func)(void *cookie, ifnet_t interface, protocol_family_t protocol, mbuf_t *data);
```

## Parameters

- `cookie`: The cookie specified when this filter was attached.
- `interface`: The interface the packet is being transmitted on.
- `data`: The fully formed outbound packet in a chain of mbufs. The frame header is already included. The filter function may modify the packet or return a different mbuf chain.

## Return Value

Return Value Return: 0 - The caller will continue with normal processing of the packet. EJUSTRETURN - The caller will stop processing the packet, the packet will not be freed. Anything Else - The caller will free the packet and stop processing.

## Discussion

Discussion iff_output_func is used to filter fully formed outbound packets. The interface is only valid for the duration of the filter call. If you need to keep a reference to the interface, be sure to call ifnet_reference and ifnet_release.