---
title: proto_media_preout
framework: kernel
role: symbol
role_heading: Type Alias
path: kernel/proto_media_preout
---

# proto_media_preout

## Declaration

```occ
typedef errno_t (*proto_media_preout)(ifnet_t ifp, protocol_family_t protocol, mbuf_t *packet, const struct sockaddr *dest, void *route, char *frame_type, char *link_layer_dest);
```

## Parameters

- `ifp`: The interface the packet will be sent on.
- `protocol_family`: The protocol of the packet being sent (PF_INET/etc...).
- `packet`: The packet being sent.
- `dest`: The protocol level destination address.
- `route`: A pointer to the routing structure for the packet.
- `frame_type`: The media specific frame type.
- `link_layer_dest`: The media specific destination.

## Return Value

Return Value If the result is zero, processing will continue normally. If the result is non-zero, processing will stop. If the result is non-zero and not EJUSTRETURN, the packet will be freed by the caller.

## Discussion

Discussion proto_media_preout is called just before the packet is transmitted. This gives the proto_media_preout function an opportunity to specify the media specific frame type and destination.