---
name: "IP_ROUTER_ALERT"
section: "2const"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/IP_ROUTER_ALERT"
---

# IP\_ROUTER\_ALERT(2const)

pass all to-be forwarded packets

## NAME

IP\_ROUTER\_ALERT - pass all to-be forwarded packets

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <netinet/in.h>  /* Definition of IP* constants */
#include <sys/socket.h>
```

**int setsockopt(int** *sockfd***, IPPROTO\_IP, IP\_ROUTER\_ALERT,**                **const int \****enable***, sizeof(int));**

## DESCRIPTION

Pass all to-be forwarded packets with the IP Router Alert option set to this socket.

Valid only for raw sockets.

This is useful, for instance, for user-space RSVP daemons.

## ERRORS

See [**IPPROTO\_IP**(2const)](/IPPROTO_IP/2const.md). See [**setsockopt**(2)](/setsockopt/2.md). See [**ip**(7)](/ip/7.md).

## STANDARDS

Linux.

## HISTORY

Linux 2.2.

## CAVEATS

The tapped packets are not forwarded by the kernel; it is the user's responsibility to send them out again.

Socket binding is ignored, such packets are filtered only by protocol.

## SEE ALSO

[**IPPROTO\_IP**(2const)](/IPPROTO_IP/2const.md), [**setsockopt**(2)](/setsockopt/2.md), [**ip**(7)](/ip/7.md)