IPV6_ROUTER_ALERT(2const)

✨ IPV6_ROUTER_ALERT(2const) ✨

bestie. sit down. we're talking about IPV6_ROUTER_ALERT today and it is genuinely so niche and so cool 💖

okay so basically: this is the thing that lets you go "hey kernel, hand me those forwarded packets that are carrying a router alert hop-by-hop option, they're mine now" 🫶

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🎀 LIBRARY

Standard C library (libc, -lc) — yeah yeah, the usual 💅

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🌸 SYNOPSIS

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

int setsockopt(int sockfd, IPPROTO_IPV6, IPV6_ROUTER_ALERT,
               const int *val, sizeof(int));

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🦋 DESCRIPTION

Okay so here's the whole vibe: this option makes the kernel pass forwarded packets containing a router alert hop-by-hop option to this socket. That's it. That's the entire personality 🌈

important: this is allowed only for SOCK_RAW sockets. no raw socket, no alert packets, no exceptions, periodt 💀

And now the part that lowkey stresses people out: the tapped packets are not forwarded by the kernel. The kernel just goes "here you go bestie 🫴" and washes its hands of them. It is the user's responsibility to send them out again. Not optional. Not a suggestion. If you don't re-send them, they're just... gone. into the void. ✨

Now the val situation, because it is genuinely doing two jobs:

• A positive integer indicates a router alert option value to intercept. Packets carrying a router alert option with a value field containing this integer will be delivered to the socket. 🎯
• A negative integer disables delivery of packets with router alert options to this socket. 🚫

so like, positive = "yes gimme those", negative = "nvm unsubscribing." iconic behaviour honestly 💅

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🙈 ERRORS

Not gonna reinvent the wheel here — the error tea lives elsewhere:

• See IPPROTO_IPV6(2const).
• See setsockopt(2).
• See ipv6(7).

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👑 SEE ALSO

• IPPROTO_IPV6(2const)
• setsockopt(2)
• cmsg(3)
• ipv6(7)

go read those, iykyk 📚✨

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that's the whole page bestie, no cap 💖 this was Linux man-pages 6.20, dated 2025-12-02 — slay, and good luck with your raw sockets 🧚‍♀️🌸