IP_MULTICAST_ALL(2const)

💖 IP_MULTICAST_ALL 💖

okay bestie, sit down, hydrate, and let me tell you about a lil socket option with the manual-page-suffix (2const) — it's literally the delivery policy of multicast messages. That's it, that's the whole name.

It lives in the Standard C library (libc, -lc), so no exotic library hunting required, periodt. 🎀

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✨ SYNOPSIS ✨

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

int setsockopt(int sockfd, IPPROTO_IP, IP_MULTICAST_ALL,
               const int *val, sizeof(int));

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🦋 DESCRIPTION 🦋

So here's the vibe: this option lets you modify the delivery policy of multicast messages. Like, who gets to slide into your socket's DMs, basically. 💅

• If val is set to 1 (which is the default, btw), the socket will receive messages from all the groups that have been joined globally on the whole system. Not just your socket — the whole system. it's giving "everyone's invited to the party and you didn't even send the invite." 😭
• If it's set to 0, it will deliver messages only from the groups that have been explicitly joined (for example via IP_ADD_MEMBERSHIP(2const)) on this particular socket. Main character energy: if you didn't RSVP, you're not getting in. 👑

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💀 ERRORS 💀

ngl this section is short, but the lore is elsewhere — go read:

• IPPROTO_IP(2const)
• setsockopt(2)
• ip(7)

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🌸 HISTORY 🌸

This icon has been around since Linux 2.6.31. Vintage but still eating. ⭐

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🔥 SEE ALSO 🔥

• IPPROTO_IP(2const)
• setsockopt(2)
• ip(7)

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and that's the whole page bestie, no cap. this lore drop came to you courtesy of Linux man-pages 6.20, dated 2025-11-25 — go forth and multicast responsibly 🫶💖✨